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The effect of morphology and chemical characteristics of cellulose reinforcements on the crystallinity of polylactic acid

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Abstract

The aim of this work has been to study the crystallization behavior of composites based on polylactic acid (PLA) and three different types of cellulose reinforcements, viz., microcrystalline cellulose (MCC), cellulose fibers (CFs), and wood flour (WF). The primary interest was to determine how the size, chemical composition, and the surface topography of cellulosic materials affect the crystallization of PLA. The studied composite materials were compounded using a twin-screw extruder and injection-molded to test samples. The content of cellulose reinforcements were 25% by weight. The MCC and WF were shown to have a better nucleating ability than CFs based on differential scanning calorimetry and optical microscopy studies. It is difficult to visualize that transcrystallization will occur during melting process and this process is influenced by the morphological and chemical characteristics of the reinforcement. Bulk crystallization seems to be mainly dependent on the processing temperature. The cold crystallization process was shown to improve the thermal stability and storage modulus of the composites. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 101: 300–310, 2006

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... For example, Stephen et al prepared a "frangible powder form" of CNC, that is suitable for use as nanofiller in polymer materials and can be processed by direct thermal blending [17]. A great deal of research on celluloses as reinforcing materials for PLA matrix by solvent casting and melt blending have previously been carried out [18][19][20]. For example, Oksman et al reported a technique to solve the feeding difficulties and upgrade the dispersion of cellulose nanowhiskers (CNW) in PLA by pumping a slurry of plasticizer and CNWs into the melt PLA during extrusion [18]. ...
... It was found that although the addition of additives had an adverse effect, but the CNWs can enhance the final mechanical properties of PLA. In another study reported by Mathew et al, a comparison between cellulose microfibers (CMFs) and CNWs as organic fillers was done [19]. The results exhibited partial enhancements in the mechanical properties and CMFs agglomerates in the PLA matrix. ...
... To investigate the toughening mechanism, both tensile and impact fracture portions of the samples were observed using the same SEM instrument. [19]. Due to this phenomenon, the interaction among fillers become more prominent in comparison to the filler-matrix interaction, and the interfacial adhesion between CNC and PLA is poor. ...
Thesis
Chapter Title: Toughening polylactide by direct blending of cellulose nanocrystals and epoxidized soybean oil. Chapter Synopsis: Polylactide (PLA) is a bio-based polymeric material which is earth abundant in nature. It also possesses abundant strength and stiffness making it a promising material for industrial applications. However, its brittle behavior is currently limiting research work on them. As such, an eco-friendly blending approach is developed in this study in order to fabricate a ductile and toughen polylactide composites using renewable bio-based materials as a precursor. Specifically, polylactide (PLA), epoxidized soybean oil (ESO), and frangible powder form of cellulose nanocrystals (CNC) are melt-blended to prepare the ternary composite system (PLA/CNC/ESO). During the composite routing, it is found out that the ESO successfully attached to the surface of CNC which in turn results in CNC/ESO mixtures in the PLA matrix. This intrinsic combination induces cavitation which consumes the energy produced under the stretching and impacting, resulting in the turning of the PLA’s brittle phenomenon. In fact, a reasonable increase in the ductility is observed. The elongation and notched impact strength of the ternary nanocomposite are found to be ∼32% and ∼4.8 kJ/m2, respectively, which are comparatively higher than that of neat PLA or PLA/CNC composites. Differential scanning calorimetry (DSC) analyses show that the ESO layer on CNC affect the thermal characteristics of PLA in the ternary composite while thermogravimetric analysis (TGA) shows that there is an increase in the char yield of the composite. Furthermore, scanning electron microscopy (SEM) analysis shows that the synthesis approach adopted here enables a mechanistically turning of the PLA’s brittle phenomenon to ductile. [This chapter is published through John Wiley & Sons, Inc., USA. Recommended citation: Mahmud Sakil, et al. "Toughening polylactide by direct blending of cellulose nanocrystals and epoxidized soybean oil." Journal of Applied Polymer Science 136.46 (2019): 48221. DOI: https://doi.org/10.1002/app.48221]
... In Table 5, we can see that the Tg value is slightly higher for the material that does not have CNCs. It is believed that CNCs can act as an insert between the chains, favoring their mobility [2]. ...
... It can be observed in Table 5 that Tcc decreases when the concentration of the CNCs increases, which may be indicative of the nucleation effect of the CNCs [2,42]. Also, the values of T m2 are similar for the materials of PLA 20 MFC and PLA 19 MFC, which contain 1% of CNCs. ...
... Perhaps due to the low concentration of CNCs, no significant effect is observed. For those containing 5% CNCs, the shift to the left is more significant, indicating that CNCs favors nucleation and crystal growth on their surface [2]. ...
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In this work polylactic acid (PLA) based multiscale cellulosic biocomposites were prepared with the aim to evaluate the effect of the incorporation of cellulose nanocrystals (CNCs) on the PLA biocomposites reinforced with cellulose microfibers (MFCs). For this, PLA composite materials reinforced with both MFCs and with a combination of MFCs and CNCs were prepared, while keeping the content of cellulosic reinforcements constant. The thermal and mechanical properties of these multiscale PLA biocomposites were characterized by thermogravimetry (TGA), differential scanning calorimetry (DSC), flexural mechanical and, dynamic mechanical (DMA) tests. Likewise, they were characterized by Fourier transform infrared spectroscopy (FTIR) and scanning electron microscopy (SEM). The results show that the replacement of MFCs by CNCs in the 1–5% range appreciably modifies the thermal and mechanical properties of multiscale compounds. For example, they increase the thermal stability of the materials, modify the PLA crystallization process and play the role of adhesion promoters since the mechanical properties in flexure increase in the order of 40% and the storage modulus increases in the order of 35% at room temperature. Also, the addition of CNCs increases the relaxation temperature of the material from 50 to 60 °C, thereby expanding the temperature range for its use.
... Similarly, tensile strength improved from *38 to *62 MPa, indicating the increase of 63% compared to neat PPF. These improvements are the result of matrix/filler interaction (Awal et al. 2015), better stress transfer across the interphase (Mathew et al. 2006) and good mechanical properties of the used MCC (Jonoobi et al. 2010). However, the lower content of MCC (e.g., 5 wt. ...
... % or 10 wt.%) does not create any significant influence in PPF's elongation at break but further increasing of filler (15 wt.%) can slightly improve their values (*2.52 to *4.05%). It is worthy to note that, the higher content of MCC (20 wt.%) can only improve the blend's modulus (2.5 GPa) which is common behavior of thermoplastic/cellulose composites (Mathew et al. 2006). In contrast, other tensile properties such as tensile strength (*62.10 to *60.39 MPa) and elongation at break (*4.05 to *3.20%) decreases with such content of MCC. ...
Thesis
Chapter Title : Nucleation and crystallization of poly(propylene 2,5-furan dicarboxylate) by direct blending of microcrystalline cellulose: improved tensile and barrier properties. Abstract: Poly(propylene 2,5-furan dicarboxylate) (PPF) is an example of alipharomatic bio-based polyester which has a high potential for the replacement of its fossil-based terephthalate counterparts (PPT). PPF offers advantages over PPT owing to its brilliant properties. However, PPF often exhibits a slow rate of crystallization, which is a bottleneck for its successful synthesis. This has also caused limited research work on the use of PPF for the specific application. Therefore, in this study, PPF is melt compounded with microcrystalline cellulose (MCC) via twin-screw extrusion, which in turn enhances its crystallization. During its preparation, no toxic chemicals are used to modify the fibers or compatibilizers, indicating that the synthesis method follows green chemistry principles. The influence of the MCC on the thermal, structure and surface behaviors of PPF is analyzed using Fourier transform infrared spectroscopy, scanning electron microscopy, differential scanning calorimetry (DSC), thermo-gravimetric analysis and X-ray diffraction. The effect of the MCC on both non-isothermal and isothermal crystallization of PPF is also explored by using DSC. It is observed that crystallization is faster, while PPF is compounded with lower content of MCC. Similarly, the nucleating rate is intensified with the introduction of MCC. The incorporation of MCC significantly increased tensile modulus, strength and elongation of break of progressing PPF by 16%, 63% and 61%, respectively, at a content of 15 wt.% MCC. The blend also owned better oxygen and carbon dioxide barrier properties than neat PPF as a function of MCC content. This study is expected to spur further work on the synthesis of PPF composite for packaging applications. [This chapter is published through Springer. Recommended citation: Mahmud, Sakil, et al. Nucleation and crystallization of poly(propylene 2,5-furan dicarboxylate) by direct blending of microcrystalline cellulose: improved tensile and barrier properties. Cellulose (2020). https://doi.org/10.1007/s10570-020-03448-4]
... Similarly, tensile strength improved from *38 to *62 MPa, indicating the increase of 63% compared to neat PPF. These improvements are the result of matrix/filler interaction (Awal et al. 2015), better stress transfer across the interphase (Mathew et al. 2006) and good mechanical properties of the used MCC (Jonoobi et al. 2010). However, the lower content of MCC (e.g., 5 wt. ...
... % or 10 wt.%) does not create any significant influence in PPF's elongation at break but further increasing of filler (15 wt.%) can slightly improve their values (*2.52 to *4.05%). It is worthy to note that, the higher content of MCC (20 wt.%) can only improve the blend's modulus (2.5 GPa) which is common behavior of thermoplastic/cellulose composites (Mathew et al. 2006). In contrast, other tensile properties such as tensile strength (*62.10 to *60.39 MPa) and elongation at break (*4.05 to *3.20%) decreases with such content of MCC. ...
Article
Full-text available
Poly(propylene 2,5-furan dicarboxylate) (PPF) is an example of alipharomatic bio-based polyester which has a high potential for the replacement of its fossil-based terephthalate counterparts (PPT). PPF offers advantages over PPT owing to its brilliant properties. However, PPF often exhibits a slow rate of crystallization, which is a bottleneck for its successful synthesis. This has also caused limited research work on the use of PPF for the specific application. Therefore, in this study, PPF is melt compounded with microcrystalline cellulose (MCC) via twin-screw extrusion, which in turn enhances its crystallization. During its preparation, no toxic chemicals are used to modify the fibers or compatibilizers, indicating that the synthesis method follows green chemistry principles. The influence of the MCC on the thermal, structure and surface behaviors of PPF is analyzed using Fourier transform infrared spectroscopy, scanning electron microscopy, differential scanning calorimetry (DSC), thermo-gravimetric analysis and X-ray diffraction. The effect of the MCC on both non-isothermal and isothermal crystallization of PPF is also explored by using DSC. It is observed that crystallization is faster, while PPF is compounded with lower content of MCC. Similarly, the nucleating rate is intensified with the introduction of MCC. The incorporation of MCC significantly increased tensile modulus, strength and elongation of break of progressing PPF by 16%, 63% and 61%, respectively, at a content of 15 wt.% MCC. The blend also owned better oxygen and carbon dioxide barrier properties than neat PPF as a function of MCC content. This study is expected to spur further work on the synthesis of PPF composite for packaging applications. Graphic abstract
... The surface of plain PLLA, not presented herein, appears quite smooth as expected. Wood particles, as well reported in the literature [12,16,96], reveal quite a smooth surface with clearly visible fiber-like structure consisting of different strands' bundles. Morphology of the PLLA composite containing 10 wt % of wood is presented in Figure 6a. ...
... The micrograph presents a filler particle pulled out and separated from the PLLA matrix, with no polymer traces on the wood surface. Wood particles reveal quite a smooth surface, thus it is difficult to achieve sufficient interfacial adhesion via mechanical interlocking [96] or chemical bonding due to different polarities of components. Poor adhesion in turn results in the creation of voids on the filler-matrix borders, clearly seen in Figure 6a, which result in premature failure of the entire system as proven in [25,26]. ...
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Bio-based composites made of poly(l-lactic acid) (PLLA) and pine wood were prepared by melt extrusion. The composites were compatibilized by impregnation of wood with γ-aminopropyltriethoxysilane (APE). Comparison with non-compatibilized formulation revealed that APE is an efficient compatibilizer for PLLA/wood composites. Pine wood particles dispersed within PLLA act as nucleating agents able to start the growth of PLLA crystals, resulting in a faster crystallization rate and increased crystal fraction. Moreover, the composites have a slightly lower thermal stability compared to PLLA, proportional to filler content, due to the lower thermal stability of wood. Molecular dynamics was investigated using the solid-state 1H NMR technique, which revealed restrictions in the mobility of polymer chains upon the addition of wood, as well as enhanced interfacial adhesion between the filler and matrix in the composites compatibilized with APE. The enhanced interfacial adhesion in silane-treated composites was also proved by scanning electron microscopy and resulted in slightly improved deformability and impact resistance of the composites.
... Crystallinity of the commercial and inhouse-made PCTs, as well as the pultruded thermoplastic GF/PP flat laminates and bars, was determined in accordance with the technique described in [37] using differential scanning calorimetry (DSC) analysis. The measurements were performed on a DSC-60Plus (Shimadzu, Japan) in a temperature range of • C, at a heating rate of 5 • C/min, and an inert gas flow rate of 60 mL/min. ...
... The results of DSC, TGA analysis, and the calculated crystallinity values of commercial and inhouse-made PCTs, pultruded thermoplastic GF/PP, and flat laminates and bars are presented in Table 1. The crystallinity of each material was obtained as follows [37]: ...
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The choice of a manufacturing process, raw materials, and process parameters affects the quality of produced pre-consolidated tapes used in thermoplastic pultrusion. In this study, we used two types of pre-consolidated GF/PP tapes—commercially available (ApATeCh-Tape Company, Moscow, Russia) and inhouse-made tapes produced from commingled yarns (Jushi Holdings Inc, Boca Raton, FL, USA)—to produce pultruded thermoplastic Ø 6 mm bars and 75 mm × 3.5 mm flat laminates. Flat laminates produced from inhouse-made pre-consolidated tapes demonstrated higher flexural, tensile, and apparent interlaminar shear strength compared to laminates produced from commercial pre-consolidated tapes by as much as 106%, 6.4%, and 27.6%, respectively. Differences in pre-consolidated tape manufacturing methods determine the differences in glass fiber impregnation and, thus, differences in the mechanical properties of corresponding pultruded composites. The use of commingled yarns (consisting of matrix and glass fibers properly intermingled over the whole length of prepreg material) makes it possible to achieve a more uniform impregnation of inhouse-made pre-consolidated tapes and to prevent formation of un-impregnated regions and matrix cracks within the center portion of the fiber bundles, which were observed in the case of commercial pre-consolidated tapes. The proposed method of producing pre-consolidated tapes made it possible to obtain pultruded composite laminates with larger cross sections than their counterparts described in the literature, featuring better mechanical properties compared to those produced from commercial pre-consolidated tapes.
... The typical XRD pattern of cellulose and PLA were shown in the different angles for each type of treated and untreated samples. While the typical sharp PLA peaks were observed approximately at degree number of 16°and 22°at 2θ value The typical cellulose peaks clearly visible at 18.8°and 32.4°at 2θ value of X-ray diffraction graph [49,50]. The intensity of the peaks increased with the addition of 3 wt% of MAPE compared with those of no addition of MAPE in 50 wt% of wood fiber filled PLA composites. ...
... This might be due to improved microstructural integrity with MAPE content. Previous studies showed that the addition of wood fiber improved the diffraction intensity peak of pure PLA polymers [49,51]. It can also be seen that the highest peak intensity was found in 40 wt% of treated wood fiber filled MAPE grafted PLA composites. ...
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The Scots pine (Pinus sylvestris L.) sapwood was impregnated with the eutectic mixture of capric acid (CA) and stearic acid (SA) as phase change material (PCM) via vacuum process for passive thermoregulation in timber buildings. The hygroscopic properties, mechanical properties, thermal energy storage (TES) characteristics and lab‐scale thermo‐regulative performance of wood/CA‐SA composite were evaluated. The produced composite from PCM was morphologically and physico‐chemically characterized by SEM, FT‐IR and XRD analysis. Thermal energy storage (TES) properties, cycling chemical/thermal reliability, and thermal degradation stability of the produced composite were determined by TG/DTA and DSC analysis. The hygroscopic tests revealed that the wood/CA‐SA composite showed low water absorption (WA) and high anti‐swelling efficiency (ASE) after 264 hours in water. Wood treatment with CA‐SA increased the bending and compression strength of wood. TG/DTA data demonstrated that the wood/CA‐SA composite left higher residue of 10.31% at 800°C than that of wood with 6.87%. The DSC measurements showed that the obtained wood/CA‐SA composite had a good TES capacity of about 94 J/g at 23.94°C. The cycling DSC results confirmed the eutectic PCM in wood indicated high chemical stability and storage/release reliability even though it was run 600 times melt/freeze. According to thermal performance test, the wood/CA‐SA composite has ability of storing excess heat in the environment and preventing the heat flow to the environment. It can be concluded that the fabricated wood/CA‐SA composite can be used for indoor temperature regulation and energy saving in timber buildings.
... As observed in our previous work, this structure is derived from the vascular bundle of the almond shell used as the cellulose source [16]. The inset at higher magnification reveals a hierarchical structure characterized by the presence of a series of parallel microbundles ascribable to crystalline cellulose entities [40,41]. SEM images of c-MCC showed in Figure 4B highlighted that the particles are in the same dimension range but less elongated than as-MCC. ...
... As observed in ou previous work, this structure is derived from the vascular bundle of the almond shell use as the cellulose source [16]. The inset at higher magnification reveals a hierarchic structure characterized by the presence of a series of parallel microbundles ascribable crystalline cellulose entities [40,41]. SEM images of c-MCC showed in Figure 4 highlighted that the particles are in the same dimension range but less elongated than a MCC. ...
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This study explores the processability, mechanical, and thermal properties of biocompostable composites based on poly (butylene adipate-co-terephthalate) (PBAT) as polymer matrix and microcrystalline cellulose (MCC) derived from softwood almond (Prunus dulcis) shells (as-MCC) as filler at two different weight concentration, i.e., 10 wt% and 20 wt%. The materials were processed by melt mixing and a commercial MCC (c-MCC) was used as filler comparison. The fibrillar shape of as-MCC particles was found to change the rheological behavior of PBAT, particularly at the highest concentration. The melt mixing processing allowed obtaining a uniform dispersion of both kinds of fillers, slightly reducing the L/D ratio of as-MCC fibers. The as-MCC particles led to a higher increase of the elastic modulus of PBAT if compared to the c-MCC counterparts. Both the MCC fillers caused a drastic reduction of the elongation at break, although it was higher than 120% also at the highest filler concentrations. DSC analysis revealed that both MCC fillers poorly affected the matrix crystallinity, although as-MCC induced a slight PBAT crystallinity increase from 8.8% up to 10.9% for PBAT/as-MCC 20%. Therefore, this work demonstrates the great potential of MCC particles derived from almond shells as filler for biocompostable composites fabrication.
... Cellulose is biodegradable and renewable [133], which is advantageous for sustainable applications. Improvements in the properties of different bioplastics, such as those based on starch and hemicellulose, with the addition of cellulose are one of its main ad- Therefore, cellulose can potentially be used for the manufacture of biomaterials such as bioplastics, and in several areas and industries (e.g., cosmetic, food, and pharmaceutical industries [130,131] due to its biodegradability, availability, non-toxicity, and biocompatibility [132]. ...
... Cellulose is biodegradable and renewable [133], which is advantageous for sustainable applications. Improvements in the properties of different bioplastics, such as those based on starch and hemicellulose, with the addition of cellulose are one of its main advantages. ...
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The accumulation of plastic wastes in different environments has become a topic of major concern over the past decades; therefore, technologies and strategies aimed at mitigating the environmental impacts of petroleum products have gained worldwide relevance. In this scenario, the production of bioplastics mainly from polysaccharides such as starch is a growing strategy and a field of intense research. The use of plasticizers, the preparation of blends, and the reinforcement of bioplastics with lignocellulosic components have shown promising and environmentally safe alternatives for overcoming the limitations of bioplastics, mainly due to the availability, biodegradability, and biocompatibility of such resources. This review addresses the production of bioplastics composed of polysaccharides from plant biomass and its advantages and disadvantages.
... Furthermore, the molding temperature also complicates the PLA injection molding process. In fact, while for most of the fossil based polymers the material can be injected into molds at room temperature, for PLA it is not possible because the resulting material proves to be amorphous with low storage modulus, especially at temperatures above its glass transition temperature [22,24]. ...
Article
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Three different commercial nucleating agents (LAK, talc, and calcium carbonate) were added at different weight percentages into poly (lactic acid) (PLA) in order to investigate the mechanical and thermo-mechanical behavior of blends in correlation to injection molding parameters. After assessing the best content of each nucleating agent, analyzing isothermal and non-isothermal crystallization, two cycle times that can be industrially adopted were selected. Crystallinity highly impacts the flexural modulus, while it improves the heat deflection temperature only when the crys-tallinity percentage is above 50%; nevertheless, an excessive crystallinity content leads to a decre-ment of impact resistance. LAK does not appear to be sensitive to cycle time while talc and calcium carbonate proved to be effective if a cycle time of 60 s is adopted. Since the choice of nucleating agent is not univocal, the identification of the best nucleating agents is subject to the technical specifications required by the application, accotuing for the most important commercial requirements (productivity, temperature, and impact resistance).
... The poor interfacial adhesion between reinforcement and matrix phase materials exhibited poor mechanical and barrier properties of the composites. 15,16 One of the methods adopted to increase the interfacial adhesion of cellulose fibers and PLA is blending them with the compatibilizers. The dispersion ability of CNC and CMF in the PLA matrix was improved by mixing with MMT as a compatibilizer. ...
Article
The cellulose reinforced polylactic acid (PLA) composites are one of the most widely explored biopolymer composites in packaging applications. In this study, the cellulose microfibers (CMF) isolated from cotton noil were reinforced with 1%, 3%, 5%, 10%, and 20% in PLA matrix by solvent casting method. The strong interfacial adhesion and enhanced dispersion of CMF in PLA polymer matrix increased the tensile, water vapor, ultraviolet (UV) light barrier properties of the composites. The ultimate tensile stress and Young's modulus of 1% CMF reinforced composites were increased by 46% and 30% respectively than that of control films. A further increase in percent CMF reinforcement of up to 20% slightly reduced the tensile strength of composites but was comparable to that of low-density polyethylene polymer. The water vapor permeability was decreased while increasing the CMF reinforcement due to the increased diffusion path by the dispersed CMF. The UV light absorbance of the composite was improved by up to 90% with the increase in CMF reinforcement by up to 20% due to the increased chromophore groups of cellulose. Hence, the PLA-CMF composites could be used for packaging and storing light and moisture-sensitive products. K E Y W O R D S biopolymers and renewable polymers, cellulose and other wood products, mechanical properties, optical properties, packaging
... CNC has been used as a reinforcing agent in polymers such as polypropylene (PP) [4] and polyvinyl alcohol (PVA) [5]. In the case of PLA, CNC has shown effectiveness as a second stage nucleating agent (during the cold crystallization process), increasing crystallinity and consequently the mechanical properties in the rubbery state (post-T g ), after undergoing a process of annealing at 80°C 1127 Mechanical behaviour of poly(lactic acid)/cellulose nanocrystal nanocomposites: A comparative study between conventional tensile test and small punch test for 3 days [6]. Similar results could be inferred from the work of Yu et al. [7]. ...
Article
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The use of nanocomposites is increasingly frequent as a way to improve the mechanical behaviour of polymers. In the specific case of poly(lactic acid) (PLA), the use of cellulose nanocrystals (CNC) as a reinforcing material is an interesting option, once the tendency of CNCs to agglomerate has been solved. One of the possible solutions to this problem is a superficial modification of CNC’s nanocrystals through a ring-opening polymerization (ROP) process. This work analyzes the use of CNC nanocrystals modified using ROP (mCNC) as a reinforcement of PLA. The mechanical properties of PLA/CNC nanocomposites are evaluated using tensile tests and small punch tests (SPT) on films prepared by extrusion calendering and post processed by compression molding. The addition of non-modified CNC promotes multiple crazing in PLA, increasing its ductility. mCNC leads to a more dispersed nanocomposite, a slight increase in the elastic modulus and a drastic decrease of crazing in tensile tests. The same tendency has been observed with SPT, and the applicability of this test in the prediction of the tensile modulus (E) of polymeric nanocomposites has been demonstrated. However, more work is needed to find the ideal SPT parameter to estimate the yield point. Keywords: Biopolymers, biocomposites, material testing, poly(lactic acid) (PLA), cellulose nanocrystals (CNC), small punch test (SPT)
... This increase may be attributed to fibers increasing the number of nucleating sites to enhance crystallinity (Avérous and Le Digabel 2006). The imperfections and defects of fiber surfaces may favor and initiate the growth of crystals, as seen in wood flour-PLA biocomposites (Mathew et al. 2006). The decreased Tc values for biocomposites was another indication of the nucleating ability of fillers (Table 4.8) (Wang et al. 2018). ...
Article
It is estimated that roughly 103, 515 tons of peach waste is produced annually in the US. The majority of the waste is disposed of in landfills, which contributes to climate change as they release 93 million metric tons of CO2 equivalent. Peach waste principally consists of remaining stone and seed after flesh removal. The agro-waste includes both cellulose and lignin, which can be utilized as a filler in plastic packaging to reduce carbon footprints and material cost. The objectives of this research are (1) to develop peach flour (PF)-filled biocomposites with a polyolefin matrix using maleic anhydride-g-high density polyethylene (MAH-g-HDPE) coupling agent resin and (2) to investigate the composites’ physicomechanical, thermal, and water absorbance changes. First, preliminary experiments examined a range of PF concentrations (5-50%) and MAH concentrations (0-17%) were tested to narrow the variability of PF and MAH loading mixture in an HDPE matrix. Preliminary experiments suggested that a 2:1 ratio of PF:CR provides maximum tensile properties. Response surface methodology (RSM) was utilized to analyze and optimize the tensile strength of the PW composite. The RSM parameters were MAH loading (5-20%), PF loading (2.5-10%), and polyolefin matrix (HDPE or polypropylene). The properties of PF-HDPE biocomposites were analyzed using several instrumental analyses. Mechanical strength (including tensile strength, elongation, and Young’s modulus) and thermal properties (thermal degradation, melting point, and crystallinity), and water resistance with the addition of PF and MAH were investigated. Biocomposite mechanical properties generally resulted in a nonsignificant decrease compared to the controls. Water absorption significantly increased with PF loading (P<0.01, =0.05). PF-PP biocomposites demonstrated a shift in thermal stability with an average 9.6% increase in Td compared to its control, whereas PF-HDPE biocomposites displayed no change in Td compared to its control. PF-PP and PF-HDPE biocomposites experienced a 36.7% and 16.0% decrease, respectively, in crystallinity with PF addition. The results provided evidence that peach byproduct can be diverted from landfills and utilized a filler in a polyolefin matrix. Polyolefin biocomposites with 2.5% PF would possess comparable tensile strength to a commercially available control. PF-polyolefin biocomposites can be used for packaging, automotive, and non-weightbearing construction parts.
... where ΔH m and ΔH c are the heat of fusion and crystallization respectively, ΔH ref is the theoretical heat of fusion for 100% crystalline PLA (93 J/g, [32]), and w is the weight fraction of PLA in the biocomposites. ...
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In this study, the accelerated weathering of PLA and its biocomposites produced with agro-industrial waste agave fibers was evaluated to better understand the lifetime of these materials. The effects of the fiber content, the fiber treatment with glycidyl methacrylate grafted PLA, and the fiber/matrix adhesion on the degradation of the materials were also analyzed. The biocomposites were prepared by dry blending, followed by compression molding using untreated and chemically modified agave fibers. The chemical treatment promoted a better fiber–matrix adhesion and lower fiber pull-outs resulting in high tensile and flexural strength values (similar to the neat PLA even with 40 wt% of fiber). Once the modification of the fiber–matrix was observed to be effective, the effect of accelerated weathering over compatibilized and uncompatibilized biocomposites was evaluated. The results showed that after accelerated weathering, the crystallinity of the biocomposites increased significantly, causing that the impact strength remains constant and, in some cases, even improved. At the same time, tensile and flexural properties were noticeably decreased. Nevertheless, the treated fibers which have better adhesion to the matrix led a better resistance to weathering degradation, which is confirmed by higher dimensional stability and lower decreases in tensile and flexural properties than biocomposites with untreated fibers.
... As a result of these properties, considerable research has been done in developing micro cellulose-based foams mostly for use in packaging applications 28,58,59 ; and in medical research 60 . Many other examples have been documented to show how reinforcement of polymers with natural fillers have led to a corresponding improvement in mechanical properties [61][62][63][64][65] . However, for lightweight foam structures which are composed of a gaseous phase dispersed in a solid phase, achieving concurrent improvement in mechanical performance alongside otherdesirable insulation properties when natural fillers are added may be quite complicated 66 . ...
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Ecological, health and environmental concerns are driving the need for bio-resourced foams for the building industry. In this paper, we examine foams made from polylactic acid (PLA) and micro cellulose fibrils (MCF). To ensure no volatile organic compounds in the foam, supercritical CO2 (sc-CO2) physical foaming of melt mixed systems was conducted. Mechanical and thermal conductivity properties were determined and applied to a net zero energy model house. The results showed that MCF had a concentration dependent impact on the foams. First structurally, the presence of MCF led to an initial increase followed by a decrease of open porosity, higher bulk density, lower expansion ratios and cell size. Differential Scanning Calorimetry and Scanning Electron Microscopy revealed that MCF decreased the glass transition of PLA allowing for a decrease in cell wall thickness when MCF was added. The mechanical performance initially increased with MCF and then decreased. This trend was mimicked by thermal insulation which initially improved. Biodegradation tests showed that the presence of cellulose in PLA improved the compostability of the foams. A maximum comparative mineralization of 95% was obtained for the PLA foam with 3 wt.% MCF when expressed as a fractional percentage of the pure cellulose reference. Energy simulations run on a model house showed that relative to an insulation of polyurethane, the bio-resourced foams led to no more than a 12% increase in heating and cooling. The energy efficiency of the foams was best at low MCF fractions.
... A significant amount of research efforts has been invested in the development, characterization and applications of polylactic acid (PLA), which is one of the most promising biomaterials as a biodegradable and renewable aliphatic polyester type of material. [1][2][3][4][5] PLA has high potential for both replacing conventional petroleum-based plastics and being used in medical applications. 2,[6][7][8][9] Lactic acid is the constituent of PLA, and it can be produced by fermentation from renewable natural sources such as cornstarch. ...
... The higher T g (69 • C) in the PLA+Wood samples compared to PLA-based filaments (~62-63 • C) can be interpreted as a delay in polymer relaxation in the presence of reinforcement due to greater crystallinity [41], as also qualitatively confirmed by the ATR measurements. This consideration, together with the existence of exothermic peaks during the first heating and the cooling phases, can be attributed to nucleating effect of the wood fibers on the PLA macromolecules, promoting crystal formation in PLA-based materials. ...
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The purpose of this study is to limit the environmental impact of packaging applications by promoting the recycling of waste products and the use of sustainable materials in additive manufacturing technology. To this end, a commercial polylactide acid (PLA)-based filament derived from waste production of bio-bags is herein considered. For reference, a filament using virgin PLA and one using a wood-based biocomposite were characterized as well. Preliminary testing involved infrared spectroscopy, differential scanning calorimetry (DSC), and thermogravimetric analysis (TGA). The effect of printing parameters (nanely bed temperature, layer thickness, top surface layers, retraction speed, and distance) on the final aesthetics of 3D printed parts was verified. The results allow us to attest that the thermal properties of recycled polymer are comparable to those of virgin PLA and biocomposite. In the case of recycled polymer, after the extrusion temperature, bed temperature, and printing speed are estabilished the lowest allowable layer thickness and an appropriate choice of retraction movements are required in order to realize 3D-printed objects without morphological defects visible to the naked eyes. In the case of wood biocomposite, the printing process was complicated by frequent obstructions, and in none of the operating conditions was it possible to obtain an aesthetically satisfying piece of the chosen geometry (Lego-type bricks) Finally, mechanical testing on the 3D printed parts of each system showed that the recycled PLA behaves similarly to virgin and wood/PLA filaments.
... Additionally, it was proven by Papageorgiou et al. [51] and Mathew et al. [52] that natural additives, such as MMT and cellulose, might significantly influence the crystallization behavior contributing to some variations in composite mechanical properties. According to the studies, these fillers may behave as nucleating factors and promote the crystalline domain's formation. ...
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The study aimed to prepare sustainable and degradable elastic blends of epoxidized natural rubber (ENR) with poly(lactic acid) (PLA) that were reinforced with flax fiber (FF) and montmorillonite (MMT), simultaneously filling the gap in the literature regarding the PLA-containing polymer blends filled with natural additives. The performed study reveals that FF incorporation into ENR/PLA blend may cause a significant improvement in tensile strength from (10 ± 1) MPa for the reference material to (19 ± 2) MPa for the fibers-filled blend. Additionally, it was found that MMT employment in the role of the filler might contribute to ENR/PLA plasticization and considerably promote the blend elongation up to 600%. This proves the successful creation of the unique and eco-friendly PLA-containing polymer blend exhibiting high elasticity. Moreover, thanks to the performed accelerated thermo-oxidative and ultraviolet (UV) aging, it was established that MMT incorporation may delay the degradation of ENR/PLA blends under the abovementioned conditions. Additionally, mold tests revealed that plant-derived fiber addition might highly enhance the ENR/PLA blend’s biodeterioration potential enabling faster and more efficient growth of microorganisms. Therefore, materials presented in this research may become competitive and eco-friendly alternatives to commonly utilized petro-based polymeric products.
... Different works suggest that the surface chemistry of fillers would affect the crystal nucleating ability of the polymer matrix [140][141][142], which is important in the foaming process. Table 3 shows the chemical characteristics of cellulosic fibers used by Ding et al. [138] in their work. ...
Article
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Polylactic acid (PLA) is a well-known and commercially available biopolymer that can be produced from different sources. Its different characteristics generated a great deal of interest in various industrial fields. Besides, its use as a polymer matrix for foam production has increased in recent years. With the rise of technologies that seek to reduce the negative environmental impact of processes, chemical foaming agents are being substituted by physical agents, primarily supercritical fluids (SCFs). Currently, the mass production of low-density PLA foams with a uniform cell morphology using SCFs as blowing agents is a challenge. This is mainly due to the low melt strength of PLA and its slow crystallization kinetics. Among the different options to improve the PLA characteristics, compounding it with different types of fillers has great potential. This strategy does not only have foaming advantages, but can also improve the performances of the final composites, regardless of the implemented foaming process, i.e., batch, injection molding, and extrusion. In addition, the operating conditions and the characteristics of the fillers, such as their size, shape factor, and surface chemistry, play an important role in the final foam morphology. This article proposes a critical review on the different SCF-assisted processes and effects of operating conditions and fillers on foaming of PLA composites.
... CNM nanocomposites have been prepared and investigated for a wide variety of thermoplastics including: poly(vinyl alcohol) (PVA), [64][65][66][67][68][69] poly(lactic acid) (PLA), [70][71][72][73][74][75][76] thermoplastic starch, [77] poly(vinyl acetate) (PVAc), [78] cellulose acetate, [79,80] thermoplastic polyurethane, [81] polypropylene (PP), [56] polyethylene (PE), [82,83] polyacrylonitrile (PAN), [84] poly(acrylonitrilestyrene-butadiene) (ABS), [85] polyamide 11, [63,86] and polyamide 12, [87,88] although this list should not be viewed as exhaustive. Early in the investigation of CNM/thermoplastic composites, solution-processed nanocomposites dominated as water-soluble polymers like PVA could be easily prepared and tested. ...
Article
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Cellulose nanomaterials (CNMs) are a class of materials that have recently garnered attention in fields as varied as structural materials, biomaterials, rheology modifiers, construction, paper enhancement, and others. As the principal structural reinforcement of biomass giving wood its mechanical properties, CNM is strong and stiff, but also nontoxic, biodegradable, and sustainable with a very large (Gton yr−1) source. Unfortunately, due to the relatively young nature of the field and inherent incompatibility of CNM with most man‐made materials in use today, research has tended to be more basic‐science oriented rather than commercially applicable, so there are few CNM‐enabled products on the market today. Herein, efforts are presented for preparing and forming cellulose nanomaterial nanocomposites. The focus is on recent efforts attempting to mitigate common impediments to practical commercialization but is also placed in context with traditional efforts. The work is presented in terms of the progress made, and still to be made, on solving the most pressing challenges—getting properties that are competitive with currently used materials, removing organic solvent, solving the inherent incompatibility between CNM and polymers of interest, and incorporation into commonly used industrial processing techniques. Cellulose nanomaterial (CNM) composites are sustainable and can compete on strength and stiffness with traditional materials. Unfortunately, research has tended to be more basic‐science oriented rather than commercially applicable, so there are few CNM‐enabled products on the market today. Efforts are presented for preparing and forming cellulose nanomaterial nanocomposites in manners practical to commercialization.
... Thus, it can be inferred that the carbon black is one of the main responsible for the changes in the crystallization of the composites. The reason for the decrease in the degree of crystallinity with increasing of carbon black content in PLA may be that PLA chains have less mobility and crystallize with great difficulty at high temperatures in the presence of carbon black [26][27][28] . The composite 75/15/15 showed Xc (in the first heating) of 25.3% lower than neat PLA (49.9%). ...
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Antistatic packaging is a very important sector since the electrostatic discharge of electronic devices can damage and/or disable these products. In addition, it is essential to dispose of this packaging correctly. In this work, the synergistic effect of the addition of lignin and carbon black on the development of antistatic and biodegradable packaging was verified. In this study, PLA was mixed with lignin and carbon black and the composites were prepared using a high-speed thermokinetic homogenizer where the melting of the PLA and the blend with fillers occurred by friction. The composites were characterized by Izod impact tests, scanning electron microscopy, thermal properties, electrical characterization and biodegradation tests in garden soil. The results show that lignin is a great option to accelerate the biodegradation of PLA in the garden soil and the carbon black acts as an antistatic agent reducing the electrical resistivity of the composites.
... where X c is the crystallinity, DH m is the experimental heat of fusion at melting point determined by DSC, DH ref is the theoretical heat of fusion of fully crystalline PLA (93 J/g) [36][37][38]. Tensile tests were performed on both the electrospun fiber mats and the fiber mat reinforced hydrogel composites using a dynamic mechanical analyzer (DMA, TA Instrument Q800, USA) in controlled force mode. Fiber mats and composite hydrogel films were cut into 20 Â 5 mm 2 rectangular strips before being mounted into the clamps. ...
Article
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Carboxy-methyl-cellulose (CMC) hydrogels, prepared in the presence of a crosslinker and photoinitiator, were reinforced with 3.7 wt% electrospun PLA fibers to create CMC hydrogel composites. To improve fiber-matrix adhesion, electrospun fiber mats based on hybrids of PLA and amphiphilic block copolymer (BCP) poly(D,L-lactide)-block-poly[2-(dimethylamino)ethyl methacrylate] (PLA-b-PDMAEMA) were produced. The presence of PDMAEMA at the fiber surface induced hydrophilic surface properties, which could be controlled by varying the PDMAEMA chain length. PDMAEMA was quaternized and co-electrospun with PLA fibers, which further enhanced the interaction between fibers and hydrogel matrix via ionic interactions. Physicochemical properties of the electrospun fiber mats and their CMC hydrogel based composites were assessed and revealed a nearly two orders of magnitude increase in modulus. Continuous electrospun fiber mats were chopped into discontinuous fibers to create short fiber reinforced CMC hydrogels. Rheological properties of these reinforced hydrogels incorporating 0.5 wt% discontinuous fibers were evaluated and showed potential as injectable composite systems for biomedical applications.
... , and W PLA are the melting enthalpy, cold crystallization enthalpy, enthalpy of neat PLA (93 Jg -1 ) [29,30], and weight fraction of PLA in PLA/HC composites. ...
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This study introduces a novel concept of polymer/rice straw hydrochar composite incorporation at different loadings (5%, 10%, 15%, and 20%), produced from microwave-induced hydrothermal carbonization (HTC) of rice straw to polylactide (PLA) for production of polylactide/hydrochar (PLA/HC) composites. Higher storage modulus was found for PLA/HC composites than that of neat PLA, confirming the formation of a network structure between PLA and hydrochar. Further, the storage modulus is directly proportional to the amount of hydrochar loading added to the PLA matrix. SEM images suggest that the neat PLA displays a smooth, soft surface. At the same time, polymer/hydrochar blends showed irregular voids and cracks due to the porous structure of hydrochar, allowing PLA to infiltrate through pores of the hydrochar. The tensile modulus of neat PLA was increased from 2.627 GPa for neat PLA to 4.376 GPa, 4.895 GPa, 5.217 GPa, and 6.182 GPa for PLA/HC composites of 5%, 10%, 15%, and 20% hydrochar loadings, respectively. The thermal degradation temperature of the composites was 335-360 oC, which is slightly less than that of neat PLA but still stable up to the range of process and applications of PLA (30-240 oC) without compromising thermal degradation.
... The impact resistance of a composite is the measure of the total energy dissipated in the material before final failure occurs. 34 Impact strength of composites depends on fibers, matrix, fiber-matrix interface, bonding strength of the matrix with reinforcement, and the test conditions. The impact strength of the composites is not changed at a lower fiber loading, because the lower fiber loading of fibers does not work when the fracture occurs. ...
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This paper focuses on the mechanical behavior of Polylatic acid reinforced Basalt and Bagasse fibers. The most important aspect in formulating this hybrid composite with better mechanical properties is the optimization of interfacial bonding between the reinforcing bagasse fiber and basalt fiber and polymer matrix. The composite of different weight proportion of the materials is compounded using twin screw extruder. The specimens were prepared by injection molding and subjected to various mechanical testing under tensile, flexural, and impact loads. It was found that 84 wt% of polylactic acid, 12 wt% of Basalt fiber and 4 wt% of Bagasse fiber composite exhibits better mechanical properties compared to other composites taken for study in this research. The better tensile, flexural, and impact strength of 52.8 MPa, 82.2 MPa, and 3.39 KJ/m2 were observed. The results show that the fiber content in weight percentage is playing a major than the fiber length on the improvement of tensile, flexural, and impact properties. The mechanical behavior obtained through experiments witnessed that Bagasse/Basalt fiber reinforcement in polylactic acid composites can be used as medium-load applications because of its low cost and ease of decomposability. The scanning electron microscope photography of the tested specimens shows better interfacial bonding between matrix and fibers. Also, the water absorption test indicates increase in fiber content increases the water absorption rate, reveals good degradation property of the composite. Additionally, the use of Bagasse fiber promotes the degradation of the material after its life time.
... The thermal properties of TCP, PLA, and TCP-PLA composite were investigated using Differential Scanning Calorimetry (DSC) (DSC 250, TA instruments, New Castle, DE, USA). The degree of crystallinity (X cw %) was calculated using Equation (1) where H m is the melt enthalpy, w f is the weight fraction of PLA, and H c is the melt enthalpy of 100% crystalline PLA and is equal to 93 J/g [39]. ...
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The primary goal of this study is to develop and analyze 3D printed structures based on a well-known composite known as β-Tricalcium Phosphate (TCP)– polylactic acid (PLA). There are some interesting aspects of this study. First, we developed 3D printable TCP–PLA composite filaments in-house, with high reproducibility, by a one-step process method using a single screw extruder. Second, we explored the physicochemical properties of the developed TCP–PLA composite filaments. Third, we investigated the effect of an FDM-based nozzle temperature of 190 °C, 200 °C, 210 °C, and 220 °C on the composite’s crystallinity and rheological and mechanical properties. Results confirmed the successful development of constant-diameter TCP–PLA composite filaments with a homogeneous distribution of TCP particles in the PLA matrix. We observed that a higher nozzle temperature in the FDM process increased the crystallinity of the printed PLA and TCP–PLA structures. As a result, it also helped to enhance the mechanical properties of the printed structures. The rheological studies were performed in the same temperature range used in the actual FDM process, and results showed an improvement in rheological properties at higher nozzle temperatures. The bare polymer and the composite polymer-ceramic melts exhibited lower viscosity and less rigidity at higher nozzle temperatures, which resulted in enhancing the polymer melt flowability and interlayer bonding between the printed layers. Overall, our results confirmed that 3D printable TCP–PLA filaments could be made in-house, and optimization of the nozzle temperature is essential to developing 3D printed composite parts with favorable mechanical properties.
... It can be seen that injection-molded PLLA exhibited only one melting peak at 164.1°C, attributed to homocrystallites (hc), whereas sc-PLA and the two cellulose fibers/sc-PLA composites (based on Lyocell and flax) showed multiple melting peaks at 160-180°C and 222-225°C, which were assigned to melting of hc and stereocomplex crystallites (sc), respectively. That is to say, sc crystallites were formed The two cellulose fiber/sc-PLA composites showed higher stereocomplex melting temperatures and lower homocomplex melting temperatures, especially notable in the Lyocell/sc-PLA composites, indicating the existence of more perfect sc and less perfect hc in composites, which may be related to fiber surface topography (Mathew et al. 2006). ...
Article
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A commonly used natural cellulose fiber (flax) and a regenerated cellulose fiber (Lyocell) were used at 20 wt% to reinforce polylactide stereocomplex (sc-PLA) composites. Composites were prepared by melt compounding cellulose fibers and an equivalent proportion of PLLA/PDLA, followed by injection molding. The structures and properties of these two kinds of cellulose fiber/sc-PLA composites were compared and evaluated. The results showed that the total crystallinity and stereocomplex crystallite content of composites could be increased by reinforcing with cellulose fibers, and Lyocell fibers were more effective in accelerating crystallinity and the formation of stereocomplex crystallites than flax fibers. Mechanical properties of Lyocell fibers were much poorer than those of flax fibers, and the interfacial adhesion values of Lyocell/sc-PLA composites were inferior to those of flax/sc-PLA composites. Lyocell/sc-PLA composites showed higher impact strength and similar tensile strength vs. flax/sc-PLA composites, but the Young’s modulus values of Lyocell/sc-PLA composites were lower than those of flax/sc-PLA composites. The Vicat softening temperatures of both flax/sc-PLA and Lyocell/sc-PLA composites were increased to nearly 100 °C higher than that of PLLA. Lyocell/sc-PLA composites showed the highest Vicat softening temperature of ~ 170 °C.
... Therefore, a lowering of the glass transition temperature occurs due to poor compatibility between wood and PLA [24]. The poor interfacial compatibility is the reason of higher interfacial tension between PLA and wood powder [24]; higher interfacial tension is the result of higher crystallinity of wood powder and PLA composite [81]. The glass transition, cold crystallisation and melting temperature of wood powder based 3D printed samples have shown to be lower than those of PLA [60] and the amount of wood content has no significant effect on thermal properties (Fig. 8d) [24,60]. ...
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Three-dimensional (3D) printing is a technology that, for a multitude of raw materials, can be used in the production of complex structures. Many of the materials that currently dominate 3D printing (e.g. titanium, steel, plastics, and concrete) have issues with high costs and environmental sustainability. Wood powder is a widely available and renewable lignocellulosic material that, when used as a fibre component, can reduce the cost of 3D printed products. Wood powder in complex with synthetic or natural binders and has potential for producing a wide variety of products and for prototyping. The use of natural binders along with wood powder can then enable more sustainable 3D printed products. However, 3D printing is an emerging technology for many applications and more research is needed. This review aims to provide insight into wood powder as a component in 3D printing, properties of resulting products, and the potential for future applications.
... As expected, pre-orientation of the nanocomposites affected the orientation and dramatically increased the mechanical properties compared to the undrawn materials. The mechanical properties of the PLA nanocomposites depend on several factors: (i) the adhesion between the PLA matrix and reinforcement phase, (ii) the aspect ratio of the reinforcement phase, (iii) the orientation and of the reinforcement and its ability to nucleate, (iv) the stress-transfer efficiency of the interface, and (v) the degree of crystallinity of the matrix [28][29][30]. ...
Article
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The orientation of polymer composites is one way to increase the mechanical properties of the material in a desired direction. In this study, the aim was to orient chitin nanocrystal (ChNC)-reinforced poly(lactic acid) (PLA) nanocomposites by combining two techniques: calendering and solid-state drawing. The effect of orientation on thermal properties, crystallinity, degree of orientation, mechanical properties and microstructure was studied. The orientation affected the thermal and structural behavior of the nanocomposites. The degree of crystallinity increased from 8% for the isotropic compression-molded films to 53% for the nanocomposites drawn with the highest draw ratio.The wide-angle X-ray scattering results confirmed an orientation factor of 0.9 for the solid-state drawn nanocomposites. The mechanical properties of the oriented nanocomposite films were significantly improved by the orientation, and the pre-orientation achieved by film calendering showed very positive effects on solid-state drawn nanocomposites: The highest mechanical properties were achieved for pre-oriented nanocomposites. The stiffness increased from 2.3 to 4 GPa, the strength from 37 to 170 MPa, the elongation at break from 3 to 75%, and the work of fracture from 1 to 96 MJ/m3. This study demonstrates that the pre-orientation has positive effect on the orientation of the nanocomposites structure and that it is an extremely efficient means to produce films with high strength and toughness. Keywords: PLA; chitin nanocrystals; nanocomposites; extrusion; compression molding; directional orientation; X-ray; mechanical properties
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Poly(lactic acid) (PLA) is a potential biodegradable polymer to replace petroleum-based plastic, however, its main drawback is brittleness because of slow crystallization rate. To overcome this limitation, compounding with some additives is the most chosen choice due to easy and effective preparation. In this study, an epoxidized soybean oil (ESO) and a microcrystalline cellulose (MCC) were applied as a plasticizer and a nucleating agent, respectively. The PLA was compounded with ESO and MCC by using a twin-screw extruder. The product sheets were prepared by using a chill-roll cast film extruder. Change of thermal property after adding ESO and MCC was investigated by a differential scanning calorimeter. Mechanical property of the prepared sheet was carried out by using a universal testing machine in a tensile mode. Microstructure of the sheets was also studied by wide angle X-ray diffraction (WAXD) and small angle X-ray scattering (SAXS) techniques. The results showed that ESO assisted plasticization while the MCC induced crystallization of PLA. Also, ESO and MCC eased flowability and alignment of PLA microstructure in machine direction.
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High hemicellulose and lignin content MFC (MFLC) was isolated from chemi-thermomechanical pulp (CTMP), and surface acetylation used to significantly decrease its polarity. This modification of MFLC provided good dispersibility in PLA when used for biocomposites fabrication via a solvent casting method. MFLC exhibited higher modification efficiency compared to lignin-free MFC. Base-catalysed surface acetylation unchanged the crystalline structure of MFLC. Detection of the hydrogen bond between acetylated MFLC (Ac-MFLC) and PLA confirmed its role in improvement of the mechanical performance, thermal properties and crystallinity of the biocomposite with Ac-MFLC acting as an effective reinforcing and nucleating agent. The approach confirms the suitability of surface functionalization of MFLC for fabrication of biocomposites for a wide range of applications such as packaging and biomedical products.
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A series of biodegradable poly (butylene succinate-co-terephthalate) (PBST) with different aromatic units content was synthesized and then melt blended by adding cellulose nanocrystals (CNCs) to manufacture the full organic composites. A network-like structure of CNCs in PBST matrix was evaluated by rheometer. The storage modulus and complex viscosity at low frequency region were significantly enhanced with increasing CNC content. Meanwhile, the decreasing tanδ and flow index were attributed to the excellent interaction between PBST and CNCs. When PBST has a content of the aromatic unit exceeds 30 mol%, the crystallization temperatures increased with increasing CNC contents. On the other hand, when PBST has 30 mol% content of the aromatic unit, the cold crystallization temperatures decreased with increasing CNC contents. These above observation in crystallization properties suggested that the CNC make a role of heterogeneous nucleation in PBST matrix. The result of mechanical properties evaluated by dynamic mechanical analysis showed a good reinforcement effect of the addition of stiff CNC. The PBST/CNC composites were suitable for cell growth and might have a potential as biomedical materials, which is confirmed by MTT assay.
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Poly(butylene 2,5-furandicarboxylate) (PBF) derived from 2, 5-furandicarboxylic acid (FDCA) is an emerging bio-based alipharomatic polyester that is expected to replace its fossil-based terephthalate and naphthate homologues. PBF holds excellent gas barrier properties, but its slow rate of crystallization might restrict wider applications. To improve the rate of crystalization, it was melt-blended with crystalline micro-cellulose (CMC) to prepare a composite through twin-screw extrusion. To ensure environmental friendly conditions, neither chemicals to modify fibers nor compatibilizers to improve the filler/matrix interaction were used. Size exclusion chromatography (SEC), Fourier transform infrared (FTIR) spectroscopy, scanning electron microscopy (SEM), differential scanning calorimetry (DSC), thermo-gravimetric analysis (TGA) and X-ray diffraction (XRD) were used to characterize the composite. It was observed that a longer blending duration (cyclic mode) leads to a greater reduction in molecular weight (Mw) in the presence of CMC, which can be avoided by using a shorter blending duration (direct mode). The mechanical properties of the composite showed an increase in Young's modulus by approximately 23 % and 36 % with respect to reference PBF for the cyclic and direct mode respectively. It was further observed that, although the elongation at break and tensile strength has decreased, it has improved gas barrier properties. Thermal analysis shows faster nucleation of PBF in the presence of CMC with a minor effect on its thermal degradation. [This is a forthcoming article]
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The interest on poly(lactic acid) (PLA)/poly(methyl methacrylate) (PMMA) blends has increased during the last years due to their promising properties. The novelty of the current work focuses on the preparation and characterization of biocomposites based on PLA/PMMA matrix and NaOH-treated sisal fibers. The effect of the addition of treated sisal fibers on the physico-mechanical properties of high polylactide content composites was studied. For this purpose, PLA/PMMA blend (80/20 wt%) was prepared by melt-blending and reinforced with different fiber contents. Although composites showed interesting specific tensile properties, the estimated heat deflection temperature (HDT), that is, the maximum temperature at which a polymer system can be used as a rigid material, barely increased 4°C respect to unreinforced system. After the annealing process, the HDT of the unreinforced polymer blend increased around 25°C, whereas the composites showed an increase of at least 38°C. Nonetheless, the specific tensile strength of composite decreased approximately 48% because the adhesion between fiber and polymer matrix was damaged and cracks were formed during annealing process.
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In recent years, composites consisting of polymers and cellulosic materials have attracted increasing research attention. Polypropylene (PP) is among the most common polymer types found in excavated waste from landfills. Moreover, wood waste generated from wood products manufacturing such as sawdust (SD) offers a good potential for the fabrication of composite materials, and it is readily available in the environment. In this paper, wood polymer composites (WPC) consisting of recycled PP (rPP) and (SD) were prepared and characterised. A range of mechanical properties, including tensile strength, flexural properties, creep and hardness were studied, along with morphology, thermal properties, water degradation and contact angle. The results showed that the mechanical and thermal properties of rPP increased with an increase in 40 wt% of the SD content. Furthermore, the SD content significantly influenced the water uptake of the composites. Time–temperature superposition (TTS) was applied to predict the long-term mechanical performance from short-term accelerated creep tests at a range of elevated temperatures. The short-term creep test showed efficient homogeneity between the fillers and matrix with increasing temperature. The produced wood polymer composites displayed a comparable physical property to virgin polymer and wood and could potentially be used for various structural materials.
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Polylactic acid is one of the most used biopolymers due to its overall properties and biodegradability. Nevertheless, polylactic acid has important drawbacks such as brittleness, low thermal stability, and higher cost than most commodity polymers. In order to overcome those disadvantages without compromising biodegradability, the addition of wood particles and thermal annealing on the crystallinity and impact strength of wood-polylactic acid biocomposites were studied. The samples were prepared by compression and rotational molding using two different wood particles: white ash and tzalam. The results showed that thermal annealing at 100 °C, 40 minutes, increased the crystallinity up to 60 % and also improved the thermal stability of polylactic acid and its biocomposites as determined via dynamic mechanical analysis. The specimens not exposed to thermal annealing exhibited important storage modulus loss above 60 °C, which mostly disappeared with the thermal treatment. Furthermore, the impact strength was substantially increased by the thermal treatment. Additionally, accelerated weathering tests showed that the thermally annealed samples had better dimensional stability growing their potential applications over a wider range of conditions.
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In this study, poly(lactic acid) (PLA) is toughened by blending with natural rubber (NR). In order to induce additional toughening, the hybrid of two clays (natural clay (CNa+) and organically‐modified clay (C20A)) showing different localization in the blend is added to the PLA/NR 70/30 blend. For the blend with CNa+ localized in the PLA matrix, linear viscoelastic response (G′, G″) of the blend does slightly change with the decreased drop size or the coarsening of NR as CNa+ content increases. On the other hand, the addition of C20A brings notable rheological response with a significant change in morphology from co‐continuous structure (< 0.5 wt%) to compatibilized morphology (> 0.5 wt%). With a small amount of clay (0.75 wt%) where G′ and G″ crossover, the mixture of two clays (CNa+/C20A 0.3/0.45 wt%) inducing different morphologies to the blend causes a synergistic effect to form cocontinuous structure, leading to a synergistic elongation at break over 100%. This study shows that the addition of a small amount of clays less than 1 wt% can induce toughening of PLA/NR by morphology control of well‐designed particle localization. Also, linear viscoelasticity analysis is useful to detect a subtle change in blend morphology.
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Improvement of the physico-mechanical properties in melt mixed bamboo-root flour reinforced biodegradable poly(ε-caprolactone) biocomposites is demonstrated, aimed at flexible cryo-packaging applications.
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PLA/hBN/Al2O3 hybrid composites with 1–30% filler concentrations were prepared in which composites with 1–2% fillers exhibit high tensile strength & modulus (8–22%, 2–12%), flexural strength & modulus (10–21%, 5–16%), storage modulus (1–14%), Tg & thermal stability (4°C, 4%), scratch hardness (37–48%), with very low CTE (22–25% & 58–66%) & surface roughness (81–97%) compared to all other samples. This improved mechanical, thermal, and decreased CTE were due to synergetic effects of hybrid fillers in the PLA matrix. The extruded filaments with 1% hybrid fillers can be used for the mass production of future bio-based substrates and enclosures.
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In the work, organic saponite (OSAP) was modified with dioctadecyl dimethyl ammonium chloride and saponite by intercalation reaction. Moreover, functionalized OSAP (FOSAP) was prepared with OSAP, BASF chain extender Joncryl ® ADR 4468 and p-phenylenediamine. The optimum reaction conditions of FOSAP were optimized by orthogonal experiment. X-ray diffraction and Fourier transform infrared spectroscopy (FTIR) results demonstrated that saponite had been successfully modified. Moreover, FOSAP/poly (lactic acid) (PLA) nanocomposites were prepared by melting intercalation with PLA and FOSAP. The mechanical properties, rheological behavior and crystallization properties of FOSAP/PLA nanocomposites were investigated. Mechanical properties showed that the impact strength and elongation at break of FOSAP/PLA nanocomposites reached 13.21 KJ/m² and 71.47%, respectively, when the amount of FOSAP in PLA was 0.3 wt%. In addition, the Cole-Cole curve showed that FOSAP had strong interfacial compatibility with PLA. Furthermore, the crystallization behaviors of PLA before and after modification during isothermal crystallization at 150 °C were investigated by Rheonaut technology for simultaneous rheology and FTIR, which demonstrated that FOSAP effectively promoted the crystallization of PLA and increased the storage modulus. Avrami equation showed that FOSAP changed the nucleation growing mode and significantly accelerated the crystallization rate of PLA, therefore the comprehensive performance of PLA was improved.
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This study focused on the effect of the processing method on the thermal, mechanical, and biodegradation properties of polylactic acid/polyhydroxybutyrate (PLA/PHB) blends and their wood biocomposites. The blending techniques were dry‐blending or twin‐screw extrusion, both followed by compression molding. PLA/PHB blends were prepared using 15 and 25% wt. of PHB and biocomposites with 20 and 30% wt. of wood particles. Moreover, a compatibilizer was used during the extrusion process to achieve better matrix‐fiber adhesion. The results showed that the crystallinity of PLA significantly increased with PHB and wood, especially after twin‐screw extrusion. The best results in tensile, flexural, and impact strength were obtained with the extruded and compatibilized PLA/PHB blends, with values higher than the neat biopolymers. The compatibilized biocomposite with 15% wt. PHB, and 20% wt. wood particles showed higher tensile, flexural, and impact properties than PLA. The biodegradation test showed that all samples were disintegrated (above 40%) after 40 days in compost medium, observing slight decreases in the biodegradation rate when PHB or wood particles were added. Even when the lower mechanical properties were obtained with the dry‐blending technique, they are still competitive for different applications, providing the possibility to produce blends and biocomposites, avoiding the extrusion process that requires more energy consumption and longer processing times.
Article
Different crystal planes of nanocrystalline often displayed diverse physical and chemical properties. In this paper, the effects of nano-ZnO with two kinds of crystal planes on crystallization, thermal stability and mechanical properties of PLLA were investigated. The results show that the (1010) planes with no-polar and low surface energy increased the chain mobility of PLLA chain, showed a plasticizing effect; the glass transition temperature, melt and cold crystallization temperature decreased by 12 °C, 10 °C and 12 °C, respectively. The size of spherulites increased and the number of spherulites decreased, the crystal form changed from mixed crystal form α, α' to unique α crystal form. However, the (0002) planes with polar and high surface energy has highly nucleating effective for PLLA, the crystallization temperature increased to 106.41 °C, the cold crystallization peak disappear. The size of spherulites decreased and the number of spherulites increased. Moreover, the (0002) planes increases the elongation at break of PLLA to 20.34% but the (1010) planes reduces to 7.49%. Their thermo-gravimetric analysis results showed the similar trend. Our results indicate that the interface wettability and compatibility between crystal planes and PLLA, which was caused by the polarity and surface energy of (1010) or (0002) planes played key role in improving the performance of polymers.
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Thesis
In the last decades, additive manufacturing -commonly referred to as 3D printing- has gained growing attention driven by increasing digitalization in industry and the biomedical sector. The expression additive manufacturing is used to describe a variety of manufacturing technologies that produce construction parts in a layer-by-layer approach based on CAD files. In comparison to traditional subtractive manufacturing processes, additive manufacturing allows the cheap production of highly complex, individualized specimens in small product series in a short time. These advantages are particularly attractive for the biomedical sector to produce surgical models and patient-specific implants. In this context, the powder bed fusion laser beam melting process of polymers (PBF-LB/P) is very capable to produce geometrically complex and porous specimens for their use as bone implants. However, the choice of suitable powder materials is very limited up to now. The available materials can be divided into two categories of unfilled polymeric powders, which are almost exclusively based on polyamide 12, and a few filled composite powders. These composite powders are physical mixtures on the micrometer scale of polyamide 12 and additives such as carbon fibers or glass beads. This limited material selection results from the high material requirements imposed by the powder bed fusion process (PBF-LB/P). A suitable powder material needs to provide a wide thermal process window, a well-developed adsorption behavior in the wavelength of the CO2 laser, and high powder flowability. In this PhD thesis, a colloid-based bottom-up process chain is presented to produce tailored supraparticles for the powder fusion process (PBF-LB/P). In a first step, polymeric and additive primary particle dispersions are prepared. These dispersions are then spray dried either as a pure polymeric dispersion to produce polymer supraparticles or as a dispersion mixture to produce composite supraparticles. The dispersion droplet serves as confinement for the self-assembly of the primary particles. The final supraparticle design can be precisely adjusted via the spray drying process conditions and the primary particle dispersions. In the first part of the thesis, a system of polymethyl methacrylate (PMMA) and silica (SiO2) is investigated with a special focus on supraparticle formation. The produced supraparticles could be of interest for dental applications. The first aim was to identify suitable spray drying process parameters to obtain spherical supraparticles with good flowability. Then, the powder flowability of the supraparticles is further improved by adjusting the supraparticle roughness. Subsequently, the structure formation of PMMA-SiO2 composite supraparticles is studied, based on different dispersion mass mixing ratios and primary particle diameter ratios. Furthermore, the drug release from PMMA composite supraparticles is investigated, comprising mesoporous drug-loaded silica (MSiO2) primary particles. Finally, the tailored PMMA and PMMA-SiO2 supraparticles with optimized product properties are applied in the powder bed fusion process (PBF-LB/P). In the second part of the thesis, a system consisting of polylactide (PLA) and calcium-containing inorganic primary particles is investigated for additively manufactured bone implants. In a first step, PLA primary particles are synthesized via the miniemulsion solvent evaporation process, while binary calcium-silica (Ca-SiO2) and nanohydroxyapatite (HAP) primary particles are produced via sol-gel processes. Subsequently, these colloidal dispersions are spray dried to form tailored supraparticles. The thermal properties and the flowability of the powder material are characterized in detail. Additionally, biocompatibility and bioactivity are tested. Furthermore, the mechanical properties of composite specimens (resulting from the supraparticles) are tested and evaluated towards their use as bone replacement materials. Finally, the produced PLA su-praparticle powders are used in the powder bed fusion process (PBF-LB/P) to fabricate multi-layered square specimens, which are later tested towards their biodegradability in biologically relevant media. In the last chapter of the thesis, the bottom-up process chain is extended to another interesting biodegradable polymer, polycaprolactone (PCL), which also finds applications in bone replacement. To this end, the thermal properties and the powder flowability are investigated and finally, the powders are processed in the powder bed fusion process (PBF-LB/P). Moreover, all polymeric composite supraparticles of PCL and PLA are produced and investigated towards their thermal and mechanical properties as a fully biodegradable bone replacement material.
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Biodegradable packaging coated with antimicrobial compounds has emerged as a new type of food packaging with potential to enhance food safety, extend shelf life and minimize plastic pollution. We have developed a polylactic acid (PLA) composite pineapple leaf fibre (PALF) biopolymer to fulfil the high demand of biodegradable materials for a potential use in food packaging. Our formulation with 10% pineapple fibre PLA/PALF composites exhibited enhanced melting temperatures and heat resistance, with a 44% reduction in the tensile strength and 2.7‐fold reduction on the strain at the break when compared with neat PLA. To impart antimicrobial activity, the PLA/PALF was coated with crude supernatants isolated from Pediococcus pentosaceus PP04 containing 1.3% w/v of nisin. This material coated with the crude extract was shown to inhibit the growth of Bacillus cereus ATCC 11778, Salmonella enterica subsp. enterica serovar Typhimurium ATCC 13311, and Escherichia coli ATCC 8739 in culture conditions, as well as minimizing the number of the tested pathogens on coated material surfaces. Polylactic acid (PLA) composite pineapple leaf fibre (PALF) biopolymer was developed and coated with crude supernatants isolated from Pediococcus pentosaceus containing nisin. This material coated with the crude extract was shown to inhibit the growth of Bacillus cereus, Salmonella enterica subsp. enterica serovar Typhimurium and Escherichia coli and minimize the number of the tested pathogens on coated material surfaces. This could be proposed as a potential food packaging material with its high melting temperature and resistance properties.
Thesis
The cellulose reinforced biopolymer composites are emerging as a potential packaging material due to their biodegradability, biocompatibility, and superior material properties. Cellulose Nanofibrils (CNF), a nanostructured cellulose can be reinforced with biopolymers such as chitosan, polylactic acid (PLA) to produce composites for flexible packaging applications. To produce highly dispersible and consistent quality CNF, cellulose pulp was subjected to a combination of mechanical (ball milling) and chemical (Carboxyl methylcellulose, CMC dispersion & NaOH swelling) pretreatments. The pretreated cellulose was fibrillated using a high-pressure homogenizer to produce CNF with up to 6% solid content and uniform fibril width from 20 to 40 nm. The CNF was reinforced with chitosan and crosslinked using citric acid to improve mechanical and hydrophobicity of flexible packaging films. The water uptake and water vapor permeability (WVP) of composite films were reduced by up to 86 and 50% respectively. The optimal amount of CNF and citric acid was determined as 20% and 25% respectively. Cellulose microfibers (CMF) produced from cotton noil was reinforced with PLA biopolymer. The tensile, WVP and UV barrier properties were improved by better dispersion stability and interfacial adhesion of CMF in PLA. The tensile stress and Young's modulus of 1% CMF reinforcement were
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This paper presents a proposition of innovative thermoplastics bio-resorbable composite materials based on polylactic acid. The compositions were prepared as an alternative to traditional biodegradable polymers, using grounded and dried plant waste in the form of buckwheat husks and dried onion husks. The main goal of the research was to develop new biopolymers prepared by extrusion for a wide range of industrial applications. Composite samples were made with the addition of 10, 20 and 30 wt.% of onion or buckwheat husks and their mechanical and thermo-physical properties were examined, with particular emphasis on the degree of crystallinity. The conducted tests showed that increasing the amount of filler decreases the mechanical properties of the composite, with the exception of the elongation at break, which slightly increased. Moreover, the 10% addition of waste positively influences the increase in the degree of crystallinity of the samples.
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Present study deals with the extraction and isolation of microcrystalline cellulose (MCC) from date palm fruit bunch stalk (DPFS) of date palm tree (Phoenix dactylifera L.) through integrated chemical method. To facilitate comparative study, each DPFS-treated, DPFS-pulp and DPFS-MCC samples were produced through respective bleaching, alkaline and acid hydrolysis treatments. The obtained samples were characterized in aspects of structural, morphological, elemental, crystallinity and thermal properties. From physicochemical analysis, fourier transform infrared ray (FTIR) and X-ray diffraction (XRD) showed the improved cellulose crystalline structure from DPFS-treated to DPFS-MCC. Morphology analysis revealed that the isolated DPFS-pulp and DPFS-MCC samples had microfibrillar structure, which achieved through the fibre disintegration by a series of chemical treatments. Moreover, the rigidity was also found the highest for isolated DPFS-MCC with 79.4% crystallinity degree. Further, the DPFS-MCC sample manifested better thermal properties for its high weight loss (84.15%), low residual weight (15.44%) and high decomposition temperature (364.2 °C) compared to the other fibre samples. Also, the DSC analysis showed the thermal behaviour which is in line with the thermal decomposition of those fibre samples. Therefore, in view of the overall result, the isolated DPFS-MCC could act as potential filler for reinforcing polymeric materials in composite field of applications.
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The effect of transcrystallinity in carbon fiber reinforced poly(p-phenylene sulfide (PPS) composites on the apparent shear strength was investigated with the single fiber pull-out test. Transcrystalline zones around the reinforcing fibers do not seem to improve the adhesion level significantly. Neighbor fibers hinder the formation of the transcrystalline zone and a ductile fracture behavior can be observed. However, the apparent strength level is slightly higher for composites containing such reinforcing neighbor fibers compared with single fiber composite samples. During annealing a brittle interface can be formed in the multifiber composite yielding a higher level of the apparent shear strength.
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The following paper summarises a number of international research projects being undertaken to understand the mechanical properties of natural cellulose fibres and composite materials. In particular the use of novel techniques, such as Raman spectroscopy, synchrotron x-ray and half-fringe photoelastic methods of measuring the physical and micromechanical properties of cellulose fibres is reported. Current single fibre testing procedures are also reviewed with emphasis on the end-use in papermaking. The techniques involved in chemically modifying fibres to improve interfacial adhesion in composites are also reviewed, and the use of novel fibre sources such as bacterial and animal cellulose. It is found that there is overlap in current international research into this area, and that there are complementary approaches and therefore further combining of these may make further progress possible. In particular a need to measure locally the adhesion properties and deformation processes of fibres in composites, with different chemical treatments, ought to be a focus of future research.
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In this study, the effects of fiber diameter, molecular weight of the matrix polymer, and interfiber spacing in glass fiber-reinforced polypropylene composites were investigated on the interfacial microstructure. The influences of the surface state of the fiber and the heat-treatment condition on the interfacial morphology and the spherulitic formation process in the matrix were also investigated. Consequently, it was found that both the fiber diameter and molecular weight of the polymer significantly influence the thickness of the transcrystalline layer. Also, as the interfiber spacing becomes smaller, the spherulites in the matrix polymer are not seen to be formed between the transcrystalline layers developed on the glass-fiber surface. In addition, the radius of the largest spherulites in the matrix polymer was found to be about the same as the thickness of transcrystalline region and to largely depend on the holding time at the crystallization temperature and cooling condition (or rate). (C) 1998 John Wiley & Sons, Inc.
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Studies on structure and properties of natural vegetable fibers (NVF) show that composites made of NVF combine good mechanical properties with a low specific mass. The high level of moisture absorption by the fiber, its poor wettability, as well as the insufficient adhesion between untreated fibers and the polymer matrix lead to debonding with age. To build composites with high mechanical properties, therefore, a surface modification of the fibers is necessary. The existing physical and chemical NVF modification methods—e.g., plasma treatment or graft copolymerization—which are used for the development of NVF–polymer composite properties is discussed. It is shown that modified cellulose fiber–polymer interaction mechanisms are complex and specific to every definite system. By using an coupling agent, like silanes or stearin acid, the Young's modulus and the tensile strength increases, dependent on the resin, until 50%. Simultaneously, the moisture absorption of the composites decreases for about 60%. With other surface modifications, similar results are obtained. © 1996 John Wiley & Sons, Inc.
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Plant fibers are of increasing interest for use in composite materials. They are renewable resources and waste management is easier than with glass fibers. In the present study, longitudinal stiffness and strength as well as morphology of unidirectional sisal–epoxy composites manufactured by resin transfer molding (RTM) were studied. Horseshoe-shaped sisal fiber bundles (technical fibers) were nonuniformly distributed in the matrix. In contrast to many wood composites, lumen was not filled by polymer matrix. Technical sisal fibers showed higher effective modulus when included in the composite material than in the technical fiber test (40 GPa as compared with 24 GPa). In contrast, the effective technical fiber strength in the composites was estimated to be around 400 MPa in comparison with a measured technical fiber tensile strength of 550 MPa. Reasons for these phenomena are discussed. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 84: 2358–2365, 2002
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Biodegradable composites were prepared using microcrystalline cellulose (MCC) as the reinforcement and polylactic acid (PLA) as a matrix. PLA is polyester of lactic acid and MCC is cellulose derived from high quality wood pulp by acid hydrolysis to remove the amorphous regions. The composites were prepared with different MCC contents, up to 25 wt %, and wood flour (WF) and wood pulp (WP) were used as reference materials. Generally, the MCC/PLA composites showed lower mechanical properties compared to the reference materials. The dynamic mechanical thermal analysis (DMTA) showed that the storage modulus was increased with the addition of MCC. The X-ray diffraction (XRD) studies on the materials showed that the composites were less crystalline than the pure components. However, the scanning electron microscopy (SEM) study of materials showed that the MCC was remaining as aggregates of crystalline cellulose fibrils, which explains the poor mechanical properties. Furthermore, the fracture surfaces of MCC composites were indicative of poor adhesion between MCC and the PLA matrix. Biodegradation studies in compost soil at 58°C showed that WF composites have better biodegradability compared to WP and MCC composites. The composite performances are expected to improve by separation of the cellulose aggregates to microfibrils and with improved adhesion. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 97: 2014–2025, 2005
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An intercalated polylactide (PLA)/layered silicate nanocomposite was prepared by simple melt extrusion of PLA and organically modified montmorillonite. The detailed crystallization kinetics and morphology of neat PLA before and after nanocomposite preparation were studied by using polarized optical microscopy, light scattering, differential scanning calorimetric, and wide-angle X-ray diffraction analyses. The overall crystallization rate and spherulitic texture of pure PLA were strongly influenced in the presence of montmorillonite particles.
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Mechanical properties of standard decorticated and hand isolated flax bast fibres were determined in tension as well as in compression. The tensile strength of technical fibre bundles was found to depend strongly on the clamping length. The tensile strength of elementary flax fibres was found to range between 1500 MPa and 1800 MPa, depending on the isolation procedure. The compressive strength of elementary flax fibres as measured with a loop test lies around 1200 MPa. However, the compressive strength can be lowered severely by the decortication process. The standard decortication process induces kink bands in the fibres. These kink bands are found to contain cracks bridged by microfibrils. The failure behaviour of elementary flax fibres under compression can be described as similar to the failure behaviour of a stranded wire.
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The focus in this work has been to study if natural fibres can be used as reinforcement in polymers based on renewable raw materials. The materials have been flax fibres and polylactic acid (PLA). PLA is a thermoplastic polymer made from lactic acid and has mainly been used for biodegradable products, such as plastic bags and planting cups, but in principle PLA can also be used as a matrix material in composites. Because of the brittle nature of PLA triacetin was tested as plasticizer for PLA and PLA/flax composites in order to improve the impact properties. The studied composite materials were manufactured with a twin-screw extruder having a flax fibre content of 30 and 40 wt.%. The extruded compound was compression moulded to test samples. The processing and material properties have been studied and compared to the more commonly used polypropylene flax fibre composites (PP/flax). Preliminary results show that the mechanical properties of PLA and flax fibre composites are promising. The composite strength is about 50% better compared to similar PP/flax fibre composites, which are used today in many automotive panels. The addition of plasticizer does not show any positive effect on the impact strength of the composites. The study of interfacial adhesion shows that adhesion needs to be improved to optimise the mechanical properties of the PLA/flax composites. The PLA/flax composites did not show any difficulties in the extrusion and compression moulding processes and they can be processed in a similar way as PP based composites.
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The morphology and crystal growth of poly(l-lactic acid), PLLA have been studied from the melt as a function of undercooling and molecular weight using hot stage microscopy. Attention has been given to the application of growth rate equation on the growth rate data of PLLA and thus various nucleation parameters have been calculated. The criteria of Regime I and Regime II types of crystallization has been applied for the evaluation of substrate lengths.
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Nanocomposite materials were obtained using glycerol plasticized starch as the matrix and a colloidal suspension of cellulose whiskers as the reinforcing phase. The cellulose whiskers, prepared from tunicin, consisted of slender parallelepiped rods with a high aspect ratio. After mixing the raw materials and gelatinization of starch, the resulting suspension was cast and evaporated under vacuum. The composites were conditioned at various moisture contents in order to evaluate the effect of this parameter on the composite structure. The resulting films were characterized using scanning electron microscopy, differential scanning calorimetry, water absorption experiments, and wide-angle X-ray scattering. An accumulation of plasticizer in the cellulose/amylopectin interfacial zones was evidenced. The specific behavior of amylopectin chains located near the interface in the presence of cellulose probably led to a transcrystallization phenomenon of amylopectin on cellulose whiskers surface.
An experimental model of acute thrombosis was developed in pentobarbital- anesthetized ferrets. A 10-min anodal electrical stimulation of 1 mA was delivered to the external surface of the carotid artery while measuring carotid blood flow (CBF). This produced an occlusive thrombus in all vehicle-treated ferrets within 41 +/- 3 min with an average weight of 8 +/- 1 mg (n = 7). These thrombi were enriched in both platelets and fibrin and were adherent at the site of transmural vascular injury as determined by light and electron microscopy. To determine the model's sensitivity to antiplatelet drugs, aspirin or a thromboxane (TxA2) receptor antagonist (ifetroban) were administered 15 min before electrical stimulation. Thrombus weight was reduced 58% by aspirin (10 mg/kg, i.v.) and 74% by ifetroban (1 mg/kg + 1 mg/kg per hr, i.v.). Both drugs also improved CBF and decreased vascular occlusion. Ferrets were more sensitive than rats to aspirin's inhibition of collagen-induced platelet aggregation as determined ex vivo in whole blood. Separate in vitro platelet aggregation studies revealed species differences in reactivity to U-46619 (TxA2 receptor agonist) and collagen in the order of human > ferret > rat, with relatively lesser variations in ADP responses. These studies identify the ferret as a useful species for evaluating antithrombotic drugs in a model in which aspirin is efficacious.
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INTEREST has arisen recently in the stress-strain properties of single wood fibres and tracheids, because of their importance to the properties of paper, board and other composite structures. Techniques for handling and mounting these fibres, which are only about 1 mm in length and 30 µ in diameter, have been developed in several laboratories and apparatus for determining stress-strain curves has been built. A survey of recent work is given by Duncker and Nordman1. To provide for simultaneous microscopical observation of the strained fibre, an apparatus was built incorporating an Instron tensile tester and a Zeiss research microscope (K. W., R. Bain and D. H. P., unpublished work). The preliminary results of this study are reported here and indicate that the deformation of wood fibres under uniform axial strain is by no means a simple matter.
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