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Creep and impact properties of wood fibre-polypropylene composites: Influence of temperature and moisture content
Abstract
Wood fibre reinforced polypropylene composites of different fibre content (40, 50 and 60% by weight) have been prepared and wood fibres (hard and long fibre) were treated with compatibiliser (MAH-PP) to increase the interfacial adhesion with the matrix to improve the dispersion of the particles and to decrease the water sorption properties of the final composite. Results indicated that impact properties were affected by moisture content. The Charpy impact strength decreased and maximum force was increased with increasing of moisture content. With the addition of MAH-PP (5% relative to the wood fibre content), damping index decreased around 145% for hard wood fibre–PP composites at 60 wt.% wood fibre content. Long wood fibre–PP composites showed more impact resistance than hard wood fibre–PP composites. Short term flexural creep tests were conducted to investigate the creep behaviour of wood fibre–PP composites. Three experimental parameters were selected: the addition of compatibiliser, temperature and wood fibre content. The addition of MAH-PP, increased creep modulus that means reduced the creep. The extent of creep resistance (creep modulus and creep strength) decreased with increasing temperature. It was also found that wood fibre content has a great effect on creep resistance which is increased with increasing wood fibre content.
... Similarly to other PMCs, PP matrix composites face a reduction of fatigue and creep life with an increase in temperature [110,111]. Viña et al. performed several fatigue tests, at different temperatures, on sheets of glass fibre-reinforced polypropylene. ...
... When exposed to higher temperatures, water diffusion is easier and enhances the moisture degradation capability. In Figure 19, the influence of temperature on the moisture absorption of a hemp-reinforced PP can be observed [110,111]. For a temperature level of 80 • C, the moisture uptake can be up to 3600% faster than when subject to ambient temperature. ...
... For a temperature level of 80 • C, the moisture uptake can be up to 3600% faster than when subject to ambient temperature. Naturally, the moisture uptake rates are highly dependent on the fibre content and nature [110,112,113], especially for natural fibres (hydrophilic by nature) [114]. Polypropylene matrix composites are being considered for use in civil construction and others under marine environments. ...
Polymer-matrix composites are widely used in engineering applications. Yet, environmental factors impact their macroscale fatigue and creep performances significantly, owing to several mechanisms acting at the microstructure level. Herein, we analyse the effects of water uptake that are responsible for swelling and, over time and in enough quantity, for hydrolysis. Seawater, due to a combination of high salinity and pressures, low temperature and biotic media present, also contributes to the acceleration of fatigue and creep damage. Similarly, other liquid corrosive agents penetrate into cracks induced by cyclic loading and cause dissolution of the resin and breakage of interfacial bonds. UV radiation either increases the crosslinking density or scissions chains, embrittling the surface layer of a given matrix. Temperature cycles close to the glass transition damage the fibre–matrix interface, promoting microcracking and hindering fatigue and creep performance. The microbial and enzymatic degradation of biopolymers is also studied, with the former responsible for metabolising specific matrices and changing their microstructure and/or chemical composition. The impact of these environmental factors is detailed for epoxy, vinyl ester and polyester (thermoset); polypropylene, polyamide and poly etheretherketone (thermoplastic); and for poly lactic acid, thermoplastic starch and polyhydroxyalkanoates (biopolymers). Overall, the environmental factors mentioned hamper the fatigue and creep performances, altering the mechanical properties of the composite or causing stress concentrations through microcracks, promoting earlier failure. Future studies should focus on other matrices beyond epoxy as well as on the development of standardised testing methods.
... The impact strength of composites is dependent on countless features, including fibre orientation, fibre volume fraction, the number of plies, or manufacturing technology. Several studies in the scientific literature were focused on the investigation of impact properties for bio-based composites [84][85][86][87][88][89]. Figure 10 shows a general comparison between traditional composites [88,90,91]. It is However, when accessible material improvement strategies are available, the effect on mechanical properties produced by exposure to the marine environment will be reduced. ...
... The impact strength of composites is dependent on countless features, including fibre orientation, fibre volume fraction, the number of plies, or manufacturing technology. Several studies in the scientific literature were focused on the investigation of impact properties for bio-based composites [84][85][86][87][88][89]. Figure 10 shows a general comparison between traditional composites [88,90,91]. It is interesting to observe that impact strength of biocomposites is similar to that achievable with traditional composites. ...
... Impact strength of bio-based and traditional composites. Data from Refs.[84][85][86][87][88][89][90][91] ...
Green composites have gained increasing attention in recent years as a sustainable alternative to traditional materials used in marine structures. These composites are made from biodegradable and renewable materials, making them environmentally friendly and reducing the subsequent carbon footprint. This review aims to provide a comprehensive overview of green composites materials and their applications in marine structures. This review includes a classification of the potential fibres and matrixes for green composites which are suitable for marine applications. The properties of green composites, such as their strength and Young’s modulus, are analysed and compared with those of traditional composites. An overview concerning current rules and regulations is presented. The applications of green composites in marine structures are reviewed, focusing on both shipbuilding and offshore applications. The main challenges in a wider application of green composites are also highlighted, as well as the benefits and future challenges.
... En revenant aux travaux mentionnés dans la table 2.5 , il est possible de remarquer que certains auteurs se sont intéressés à la résistance à l'impact de certains composites à fibres de bois courtes [9 , 53 , 54]. A.K.Beldzki et al. [54] ont étudié l'effet de la variation du taux de fibres sur la résilience du composite et ont montré que l'élévation du taux de ce constituant baisse la résistance à l'impact et accroît l'indice d 'amortissement. D'autres auteurs [47] ont travaillé sur le traitement chimique des fibres de bois notamment par estérification. ...
... L'étude bibliographique réalisée sur le polyéthylène (ou polypropylène)/fibres de bois courtes (Table 2.5) a permis de trouver des travaux concernant la durabilité en terme de fluage. Park et al. [57], Sain et al. [50] et Bledzki et al. [54] ont étudié le comportement en fluage du polyéthylène (ou polypropylène) /fibres de bois courtes. Bledzki et al. [54] et Park et al. [57] ont montré que le module de fluage ainsi que la résistance au fluage (sous chargement de flexion) du polypropylène renforcé avec des fibres de bois courtes augmentent avec la hausse du taux de fibres. ...
... Park et al. [57], Sain et al. [50] et Bledzki et al. [54] ont étudié le comportement en fluage du polyéthylène (ou polypropylène) /fibres de bois courtes. Bledzki et al. [54] et Park et al. [57] ont montré que le module de fluage ainsi que la résistance au fluage (sous chargement de flexion) du polypropylène renforcé avec des fibres de bois courtes augmentent avec la hausse du taux de fibres. Bledzki et al. [54] ont aussi démontré que ces propriétés diminuent en présence de fortes températures. ...
During the last decades, the scientific researches have been focused on the study of
the natural-fiber-reinforced composites. The works made on this type of materials have
increased because of their several advantages compared to the synthetic-fiber-reinforced
composites. Among these advantages, it is possible to highlight their low costs and their
friendly environment characters. However, the scientific works concerning the durability
(fatigue, creep, aging ... ) of natural-fiber-reinforced composites are relatively limited.
Therefore, this limit can slow down the exploitation of these composites in the industrial field knowing that certain mechanical parts can be under cyclic loading and/or
hygrothermal aging (moisture + drying) during their performances.
In this context, the PhD project ai ms to study the durability, in term of fatigue
and hygrothermal aging, of a new natural-fiber-reinforced composite made from a highdensity polyethylene, as a matrix, and short birch fibers, as reinforcements. This project begins, at the first , by studying the fatigue behavior, under bending loading, of the new composite and the effect of hygrothermal aging on this behavior. Then, this work will
focus on the modelling of the moisture diffusion kinetic inside the studied composite.
This model will allow defining the water uptake of the material taking into account
the non-fickian diffusion. Finally, a damage model will be proposed to describe the
maximum bending stress decrease during a fatigue test. Thus, the PhD project will
present a full study on the durability, in term of fatigue and hygrothermal aging, of
the short-birch-fiber-reinforced high-density polyethylene. Thallks to this study, this
composite can be used in the manufacturing of mechanical parts for performances with
cyclic bending loading and moisture. Among these parts, it is possible to mention the
gears.
Results found in the PhD project come from experimental and numerical parts.
The first part has shown that the strain level corresponding to the high Cycle Fatigue
Strength (HCFS) of the high-density polyethylelle/40% of short birch fibers is equal
to 0.91%. Moreover, this part has presented that the hygrothermal aging causes the
decrease of the HCFS of the studied material. The direct cause of this drop has been
investigated and it was proved that the creation of new damage mechanisms, after hygrothermal aging, represents this direct cause. The numerical part of the project has
allowed adopting a non-fickian diffusion model to define the water uptake inside the
studied composite. Curves fOUlld with this model have a well fittillg with those from
the experimental campaigns of immersion in distilled water. Furthermore, the numerical part has presented a damage model defining the evolution of the maximum bending
stress (residual strength) according to the number of cycles. To reduce the calculation
time and to guarantee the good quality of the results, the Cycle Jump method has
been used. The comparison made between the numerical results and those from the
experimental fatigue tests has allowed to validate the damage model and to identify
certain limits.
... Reduced deformation can also be achieved by increasing the filler concentration (Wolcott and Smith, 2004;Bengtsson et al., 2005). Additionally, the incorporation of compatibilizers usually improves interfacial adhesion and reduces the time-dependent deformation (Park and Balatinecz, 1998;Farid, 2000;Bledzki and Faruk, 2004;Lee et al., 2004). On the other hand, elevated temperature, high humidity environments or added plasticizers have a negative effect on the creep performance of the materials. ...
... 8.5) decrease with increasing fiber concentration, that is creep resistance is improved by wood fiber addition. Also working with PP-based composites, Bledzki and Faruk (2004) corroborated that adding wood fibers increased creep resistance. Moreover, they noticed that long wood fibers perform better (reduced creep deformation) than short ones. ...
... As it occurs with unfilled thermoplastics, the creep deformation of WPCs increases with temperature (Park and Balatinecz, 1998;Marcovich and Villar, 2003;Nun Äez et al., 2003Nun Äez et al., , 2004Bledzki and Faruk, 2004;Reboredo et al., 2007). Polymers are typically softened by elevated temperatures and this effect on the matrix is the controlling factor in reducing the resistance to creep of derived composites. ...
... Bledzki and Faruk 103 investigated the effects of MAPP compatibilizer on wood fiber-reinforced polypropylene with various fiber contents (40%, 50%, and 60% by weight). The Charpy impact strength of a sample is influenced by its moisture content. ...
... The mechanical properties of watersaturated specimens were reduced compared to the dry specimens, with the decrease in the flexural modulus directly influenced by water absorption. 163 Bledzki and Faruk 103 conducted a study on the utilization of MAPP to improve the bonding between polypropylene wood flour composites. The inclusion of MAH-PP resulted in a decrease in the water absorption characteristics. ...
High performance and durability are essential for goods to satisfy the needs of the expanding worldwide market. Wood plastic composites (WPCs) are materials made from a combination of wood, polymers, and additives. WPCs can be extruded, injected, compressed, or thermoformed. Presently, WPCs are manufactured using sophisticated processes including as laser sintering, fused layer modeling, and additive manufacturing. Properly managing the melt temperature and pressure is crucial in the manufacturing process of WPCs to ensure effective polymer incorporation. Natural fibers have distinct benefits for polymer composites, but they also have some serious drawbacks, like lower strength properties—especially lower impact strength than synthetic fibers—poor compatibility with hydrophobic polymers, poorer dimensional stability and moisture absorption due to hydroxly groups, a maximum processing temperature that is limited, thermal degradation above 200–220°C, and lower biological durability. The modification of the surface of the fibers improves the mentioned disadvantages of the natural fibers. High‐quality WPCs require the application of chemical or physical treatment to the wood fibers. This extensive review focused on the modification techniques applied to the surface of wood, manufacturing processes, and properties and applications of WPCs.
Highlights
Modification methods used in surface treatment of natural fibers was explained.
Properties and recent applications of wood polymer composites were given.
Optimum requirements of natural fibers and polymer matrices are given.
Fabrication methods of natural fiber composites are extensively given.
... As the wood fiber content increase, the ductile portion (PVC matrix) automatically reduced, thus decreasing the composite toughness. Bledzki et al., (2004), reported similar findings on creep and impact properties of wood fiber, polypropylene composites influence of temperature and moisture content. This suggests decrease in impact strength of natural fiber/polymer composite was usually derived from de-bonding and friction effect, especially for the composite when no fiber treatment was applied. ...
... This leads to the decrease in composite toughness. This finding was found to be in agreement with the study of Bledzki et al., (2004), who suggested that decrease in impact strength of natural fiber/polymer composite was usually derived from de-bonding and friction effect. ...
... Strengthening the interfacial adhesion reduces the water uptake behavior, since the gaps and voids content at the fiber-matrix interface is minimized to the highest extent. Silane coupling agents introduce improvement to the moisture absorption behavior and diffusivity of different natural composites up to 89% and 96%, respectively, as demonstrated by the values listed in Table 1 [126][127][128]. The coupling agent can serve The improvement that can be achieved from alkalization is subjected to the type of natural fiber. ...
... Strengthening the interfacial adhesion reduces the water uptake behavior, since the gaps and voids content at the fiber-matrix interface is minimized to the highest extent. Silane coupling agents introduce improvement to the moisture absorption behavior and diffusivity of different natural composites up to 89% and 96%, respectively, as demonstrated by the values listed in Table 1 [126][127][128]. The coupling agent can serve two main functions: it reacts with the functional groups of the matrix, and then it reacts with the -OH groups found in cellulose. ...
Natural composites can be fabricated through reinforcing either synthetic or bio-based polymers with hydrophilic natural fibers. Ultimate moisture absorption resistance at the fiber–matrix interface can be achieved when hydrophilic natural fibers are used to reinforce biopolymers due to the high degree of compatibility between them. However, the cost of biopolymers is several times higher than that of their synthetic counterparts, which hinders their dissemination in various industries. In order to produce economically feasible natural composites, synthetic resins are frequently reinforced with hydrophilic fibers, which increases the incompatibility issues such as the creation of voids and delamination at fiber–matrix interfaces. Therefore, applying chemical and/or physical treatments to eliminate the aforementioned drawbacks is of primary importance. However, it is demonstrated through this review study that these treatments do not guarantee a sufficient improvement of the moisture absorption properties of natural composites, and the moisture treatments should be applied under the consideration of the following parameters: (i) type of hosting matrix; (ii) type of natural fiber; (iii) loading of natural fiber; (iv) the hybridization of natural fibers with mineral/synthetic counterparts; (v) implantation of nanofillers. Complete discussion about each of these parameters is developed through this study.
... Consequently, investigating the mechanical behavior of wood under combined climatic changes and crack occurrence is important to improve the design of timber structures [21], [22]. Creep tests performed in uncontrolled environment are most appropriate to study the coupled impact of deferred loads and climatic variations, involving a significant contribution of mechanosorption [18]. ...
... In Fig. 12 for instance, the sharp apparent increase of MC mid January and early February indicate rainy days likely followed by wood moistening, causing a marked increase of deflection. These results are in accordance with the literature which shows that the creep rises during the moistening process of wood [21], [31]- [33]. Fig. 13 shows a zoom during 5 days (31/3-4/4/2017) taken from data of Fig. 12. Within these daily variations, the deflection increases during humidification (Fig. 13a). ...
h i g h l i g h t s Investigation of environmental and mechanical impact on notched beam used in building. We propose a methodology for the following of deflection, crack and climatic parameters. A mathematical expression of the Module of Elasticity with the shear effects is proposed. Investigation of Thermo-hydro-mechanical behavior of Pseudotsuga menziesi and Abies alba Mil. a b s t r a c t The impact of variations of relative humidity, temperature and moisture content on the creep of notched beams of Douglas fir and white fir are investigated. Indoor static 4-points bending tests are followed by outdoor creep tests of notched beams designed to trigger the breakage mode associated with the use of notched ends. The dimensions of wood specimens follow Eurocode requirements. The maximum load applied to outdoor creep tests is derived from the failure load obtained during indoor instantaneous tests. The results show that the variations of the relative humidity and temperature, coupled with the loading, play a key role in the lifetime of timber, as they accelerate its aging. In addition, the link between the changes of climatic parameters and the damage of the beams and the limit of their lifetime as structure is shown.
... Beyond this point, higher wood-weight ratios led to weaker bonding between the matrix and the fiber. These trends were also noted by Bledzki and Faruk (2004) and Facca, Kortschot, and Yan (2006). ...
Green composites consisting of renewable or biodegradable materials are becoming more popular as environmental awareness of global waste issues grows. Among them, natural composites made of polymers have proven to work exceptionally well because of their high strength, rapid breakdown after disposal, and simplicity in processing using standard techniques. In particular, competitive mechanical performances have been demonstrated by green composites having a polymer matrix reinforced with sisal, luffa, and maize fibers at different fiber percentages of 10%, 15%, and 25%. The tensile characteristics of polymer composites reinforced with these fibers are optimized in this study by the application of Taguchi and response surface methodology. By assessing characteristics such as section size, fiber content, and fiber type simultaneously, the study attempts to produce optimal biocomposite qualities, which are then experimentally tested. Tensile tests show considerable gains: the biocomposite containing 15% corn fiber showed a 21.04% increase in tensile strength. Similarly, sisal, luffa, and corn fibers all showed notable improvements in Young’s modulus, with the biocomposite showing 22.77%, 31.77%, and 20.25% increases, respectively.
... Beyond this point, higher wood-weight ratios led to weaker bonding between the matrix and the fiber. These trends were also noted by Bledzki and Faruk (2004) and Facca, Kortschot, and Yan (2006). ...
Green composites consisting of renewable or biodegradable materials are becoming more popular as environmental awareness of global waste issues grows. Among them, natural composites made of polymers have proven to work exceptionally well because of their high strength, rapid breakdown after disposal, and simplicity in processing using standard techniques. In particular, competitive mechanical performances have been demonstrated by green composites having a polymer matrix reinforced with sisal, luffa, and maize fibres at different fibre percentages of 10%, 15%, and 25%. The tensile characteristics of polymer composites reinforced with these fibres are optimised in this study by the application of Taguchi and response surface methodology. By assessing characteristics such as section size, fiber content, and fiber type simultaneously, the study attempts to produce optimal biocomposite qualities, which are then experimentally tested. Tensile tests show considerable gains: the biocomposite containing 15% corn fibre showed a 21.04 % increase in tensile strength. Similarly, sisal, luffa, and corn fibres all showed notable improvements in Young's modulus, with the biocomposite showing 22.77%, 31.77%, and 20.25% increases, respectively.
... MA plays a significant role in terms of improving compatibility, as it can form covalent bonds through its reactivity [27][28][29][30]. The ratio of MA rings in these compatibilizers carries significant information, which is defined by the acid number or the MA content/ratio, depending on the consistency of the additive [31][32][33][34]. In the additives containing functionalized MA, the acid number and the MA content/ratio do not offer sufficient information to select the appropriate compatibilizing additive for a given composite material based on its chemical structure, which would be more advantageous in many cases. ...
Ester derivatives of experimental olefin-maleic anhydride copolymers synthesized at the University of Pannonia have been investigated by both classical and instrumental analytical methods that contribute to a deeper understanding of how that type of additives functions as compatibilizers for plastics and rubbers.
Titration-based acid and saponification numbers have provided limited information about the chemical structure of the experimental copolymer compounds. A prompt, precise and low-cost method or combination of methods has been required to access to the ratio of the various derivatives not only straight after esterification but also for quality control during long-term storage considering the even stricter sustainability aspects either. Reproduction and scaling-up synthesises can be also followed by the combined measuring techniques of Fourier-transform infrared spectroscopy (FT-IR) and oscillatory rheometry. Structural changes occurred in the additives could be followed through monitoring their Ester Indices (EI) during the measurement, which can be connected also to the long-term properties. Experimental additives (AD) like AD-1 and AD-2 types with lower EI values of 21.5 % and 32.1 %, respectively, resulted in higher upper limits of the linear viscoelastic (LVE) range (15 % and 10 %). Conversely, the higher EI values of AD-3 and AD-4 led to significantly lower or even immeasurable upper limits of the LVE range. Additives with solid behaviour showed slight dependence on frequency above the crossover point that indicated strong connections disappearing.
... In recent years, researchers have conducted studies on the component materials' behavior [9][10][11][12], manufacture processes [13,14], structural forms [15][16][17], and mechanical performance [18][19][20][21] of WPCs. As the resin material exhibits viscoelastic properties, the resin molecules are displaced along the direction of the stress field under continuous loading, and the molecular chains are gradually straightened from their original bent state to result in creep [22,23]. ...
Wood-plastic composites (WPCs) are environment-friendly materials, which have broad application prospects in structures. They cannot be used for bearing structures because of poor mechanical performance and creep deformation. In order to enhance the mechanical behavior and decrease the long-term creep deformation, glass fiber reinforced plastics (GFRP) sheets and rebar reinforcement design methods are proposed. The bending static tests and creep performance tests of WPCs were conducted. The results showed that GFRP sheets and rebars improved the ultimate flexural loading capacity and deformation capacity by 257% and 165%, respectively, decreased the creep deflection effectively, and avoided shear failure. When the load level was very low, the creep deformation of WPC panels unreinforced, or reinforcement developed stably with time, and the damage did not occur within 1100 h. When the load increased to 80% of the ultimate load level, all specimens were damaged in the compression zone, the creep deformation increased quickly and unstably, bending shear failure of the unreinforced specimen occurred after 7 h, shear failure of the GFRP-sheets-reinforced specimen occurred after 1100 h, and the rebar-reinforced specimen failed after 720 h with excessive deflection deformation in the span. The reinforced effect of GFRP sheets is better. The creep strain growth rate of all specimens increased quickly at the first stage and gradually decreased at the second stage and tended to be stable. The creep calculation model was built based on the four-element model, which is simple and efficient and can make scientific and reasonable predictions of the two phases of structural transient creep and deceleration creep.
... Maleic anhydride grafted polypropylene (MAPP) is an additive coupling agent that was added in the process. It is well known as an effective compatibilizer for WPC composites [28,29]. While it develops a reaction with the hydroxyl groups in the surface of lignocellulosic fibers, MAPP diffuses to PP matrix through entanglement. ...
In this study, wood polymer composites (WPC) were produced by polypropylene (PP) as the matrix material and 30 wt% olive wood flour (OWF) as the filler material, for injection applications. Various treatments of OWF—including single treatment or co-modifications using the silane treatment, heat treatment, and maleic anhydride grafted polypropylene (MAPP) compatibilizer—were used to improve PP/OWF compatibility and mechanical properties. Structural and thermal characterization of the OWF after treatment has been implemented using Fourier transform infrared spectroscopy (FTIR) and thermogravimetric analysis (TGA). FTIR and energy-dispersive X-ray (EDX) analyses revealed the interactions between OWF and silane coupling agent. Silane and heat treatments increased the thermal stability of OWF. Results of mechanical tests revealed that the OWF increased Young's modulus values of PP/OWF composites with respect to those of pure PP, while their tensile and impact strengths decreased. Moreover, heat and MAPP treatments enhanced the mechanical properties. Heat treatment introduced higher toughness in PP/OWF composites compared to the other treatments. Scanning electron microscopy (SEM) showed the evidence of the improved interfacial adhesion and consequently mechanical properties of the PP/OWF composites by the used treatments. A further enhancement in mechanical properties was recorded for these wood polymer composites with co-modifications of OWF with MAPP.Graphical Abstract
... When increasing the wood flour content, the tensile strength of the composite increases then plateaus, and the impact strength and bending strength decrease [6][7][8]. The addition of wood flour improves the creep resistance and bending properties of the composites and decreases the creep deformation [9][10][11][12][13]. ...
Wood plastic composite (WPC) materials are mainly used as building slabs and load-bearing slabs, which will cause creep deformation, structural failure, and safety problems. Therefore, this work used high-density polyethylene and poplar wood flour as the main raw materials to prepare wood–plastic boards. The bending creep tests of wood–plastic sheets were carried out using an orthogonal test method. According to the creep test results, the influences of the WPC ratio molding temperature, pelleting temperature, coupling agent screw speed, and other technological factors on the creep properties of WPC composites under different loads are analyzed, and the influences of WPC creep properties on structural reliability are also analyzed. The results indicate that the wood–plastic ratio and screw speed are significant factors when the load is at 30% bending strength within the 24h creep test. When the load is at 50% bending strength, the wood–plastic ratio and molding temperature are the significant factors. When the load is at 70% bending strength, the wood–plastic ratio is the most significant factor. When the load is at 50% bending strength within the 240 h creep test, the wood–plastic ratio and molding temperature are significant factors. When the load is at 30% bending strength, the influence of each factor on the creeping variable is provided in the following descending order: wood–plastic ratio, molding temperature, granulation temperature, coupling agent, and screw speed, but none of them are significant factors.
... The moisture content (MC) in wood fibers (WFs) not only has an important influence on the strength and other mechanical properties of wood-plastic composites (WPCs) but also is an important factor affecting the deformation of WPCs [1]. The main chemical components of wood cell wall include hydroxyl groups with strong water absorption and other oxygen-containing groups that can form hydrogen bonds with water [2]. ...
Impulse-cyclone drying (ICD) is a new type of pretreatment method to remove the excess moisture of wood fibers (WFs) with high speed and low energy consumption. However, the process parameters are often determined by the experience of the process operators, thus the quality of WF drying lacks an objective basis and cannot be ensured. To address this issue, this study adopted the long short-term memory (LSTM) neural network, backpropagation neural network, and Central-Composite response surface method to establish a moisture content (MC) prediction model and a process parameter optimization model based on single-factor experiments. The initial MC, inlet air temperature, feed rate, and inlet air velocity were taken as the experimental factors, and the final MC was taken as the inspection index. The parameters of LSTM were optimized by particle swarm optimization (PSO) algorithm, and the predicted value of MC was fitted to the model. The PSO-optimized LSTM had higher prediction accuracy than did the typical prediction models. The optimal process for the targeted MC, which was obtained by PSO, was featured with an initial MC of 10.3%, inlet air temperature of 242°C, feed rate of 90 kg/h, and inlet air velocity of 8 m/s. PSO-LSTM could be a new approach for predicting the MC of WFs, which, in turn, could provide a theoretical basis for the application of ICD technology in the biomass composite industry.
... Various quantities of WFs, the required quantity of PP, and the coupling agent were mixed together to prepare the WPCs. Then, the granules of WPCs were again oven-dried before molding at 80 • C for 24 h [78]. For the preparation of WFCs, a twin-screw extruder, as shown in Figure 2, with aspect ratio of 40, screw diameter of 2 mm, a screw speed of 150 rpm, and a material input of 1 kg/h was set and used. ...
Waste recycling is one of the key aspects in current day studies to boost the country’s circular economy. Recycling wood from construction and demolished structures and combining it with plastics forms wood-polymer composites (WPC) which have a very wide scope of usage. Such recycled composites have very low environmental impact in terms of abiotic potential, global warming potential, and greenhouse potential. Processing of WPCs can be easily done with predetermined strength values that correspond to its end application. Yet, the usage of conventional polymer composite manufacturing techniques such as injection molding and extrusion has very limited scope. Many rheological characterization techniques are being followed to evaluate the influence of formulation and process parameters over the quality of final WPCs. It will be very much interesting to carry out a review on the material formulation of WPCs and additives used. Manufacturing of wood composites can also be made by using bio-based adhesives such as lignin, tannin, and so on. Nuances in complete replacement of synthetic adhesives as bio-based adhesives are also discussed by various researchers which can be done only by complete understanding of formulating factors of bio-based adhesives. Wood composites play a significant role in many non-structural and structural applications such as construction, floorings, windows, and door panels. The current review focuses on the processing of WPCs along with additives such as wood flour and various properties of WPCs such as mechanical, structural, and morphological properties. Applications of wood-based composites in various sectors such as automotive, marine, defense, and structural applications are also highlighted in this review.
... Previous investigations have demonstrated that the factors such as fiber and matrix type, fiber/matrix interaction, fiber/matrix volume fraction, and environmental conditions significantly affect the moisture absorption behavior. For example, in wood fiber reinforced polypropylene matrix composites it was reported that the moisture absorption rises with increasing the volume fraction of the fibers due to the higher cellulose content (Bledzki and Faruk 2004). The lignocellulose in natural fiber, which contains a high amount of polarized hydroxyl groups, is responsible for their hydrophilic nature (Zafeiropoulos 2011;). ...
Bio-composite materials, which are a serious alternative to synthetic-based fibre and matrix materials due to their high characteristics and biodegradability, cause difficulties and uncertainties for usage conditions due to their high sensitivity to climatic conditions. Scientific studies have shown that climatic factors such as temperature, humidity, radiation, UV rays, and acid rain that act synergistically in natural weathering conditions, cause degradation and changes in the bio-composite material's characteristics. Examining the material's behaviour under natural weathering conditions provides the most realistic and reliable results in terms of determining the shelf life of the material and knowing its behaviour in the usage environment. In this study, changes in thermal, mechanical, and aesthetic properties of bio-composite materials exposed to natural ventilation conditions were investigated. It has been observed that natural weathering induces dramatic decreases in thermal and mechanical properties of bio-composite materials, especially with the effect of prolonged exposure times, and causes changes in colour, surface deterioration and changes in shape.
... The residual tensile strength, creep strain, and partial deflection of WPCs were measured with a short-term bending creep test to study the effect of the wood flour content on the creep resistance and bending properties of WPCs. The results showed that with the increase in wood flour content, the creep modulus of WPCs increases, the creep strain decreases, and the bending creep resistance increases gradually [11][12][13][14]. A study of the mechanical properties and creep resistance of bamboo-fiber-reinforced regenerated polylactic acid composites (BFRPCs) showed that the BFRPCs with 60% fiber content had the best creep resistance. ...
Wood–plastic composite (WPC) materials are mainly used as flooring in buildings or as structural load-bearing plates, and will undergo creep deformation during use, resulting in structural failure and safety problems. Therefore, this work adopted the orthogonal test method to carry out creep tests on wood–plastic composites. We used the range method and variance analysis method to process the creep data and analyze the influence of the load, temperature, and relative humidity on the creep strain in specimens of wood–plastic composites. The results showed that the creep strain of the WPC specimens changed significantly with a change in the load stress, while a change in relative humidity had no significant effect on the creep strain. When the relative humidity was increased from 55% to 65%, the creep strain increased by 0.03%, but when the temperature was increased from 30 °C to 35 °C, there was no significant difference in the creep strain. However, when the temperature was increased from 30 °C to 40 °C and from 35 °C to 40 °C, a significant difference in the creep strain of the WPC specimens was observed.
... Herewith, in some cases, alternative fillers do not ensure the required physical and mechanical properties of WPC products. Hardness and stiffness are especially sensitive to experiments with the filler type [1,[8][9][10][11][12][13][14]. These indicators are the most important operating parameters of structural materials, including WPCs. ...
The paper studies issues related to physicochemical and chemical techniques for the modification of wood-polymer composites with a thermoplastic polymer matrix (WPCs) to improve their physical and mechanical properties. The physicochemical modification was performed by photochemical crosslinking with the exposure of WPC specimens to UV irradiation. Chemical modification was performed by introducing benzoyl peroxide into the material composition, leading to chemical crosslinking of polyethylene macromolecules of the WPC polymer matrix. As a result of the study, quantitative characteristics of the effect of the benzoyl peroxide content in the composite, as well as the WPC specimen UV irradiation intensity and duration on the basic physical and mechanical properties of the material have been obtained. The efficiency of physicochemical techniques for modifying WPCs has been estimated by changing the specimen properties such as Brinell hardness, water absorption, and impact strength. It has been found that the Brinell hardness increases by 80 % as compared to unmodified WPC specimens. Effective modification of wood-polymer composites with polymer matrices based on high-density polyethylene may lead to a significant improvement in the quality of products made of these materials.
... This is possibly due to the decrease in attraction to water by heat treatment. Increase in P with moisture absorption as shown by the wet untreated composites was in agreement with earlier research [36]. MPa.m 0.5 for dry treated samples at 10, 20 and 30% by weight of MP, respectively. ...
The mechanical (flexural, tensile and impact) properties and water kinetic parameters of water-absorbed hard wood (mangrove) reinforced high-density polyethylene composites were evaluated as untreated and treated mangrove dust (MD). Samples were prepared by mixing high-density polyethylene (HDPE) with MD at 10, 20 and 30% by weight in a twin-screw laboratory compounder and injection moulded into dumb-bell and rectangular-shaped test specimens for flexural, tensile and impact tests. Samples were soaked in distilled water for 1440 h at room temperature and a relative humidity of ~ 65%. The flexural strength and modulus indicated that treated composites exhibited lower decrease in values than their untreated counterparts at water equilibrium points. The dry composites maintained higher values of tensile properties, notwithstanding the treatment. Scanning electron microscopy of impact fractured surfaces showed evidence of improved MD-HDPE interfacial adhesion of treated composites in both dry and water-absorbed conditions. The water kinetics parameters such as the diffusion, sorption and permeability coefficients further show that dry composites are more water-resistant than the wet composites. Overall, the treated composites at dry and moisture-saturated conditions indicated better mechanical and moisture stability than the untreated MD/HDPE composites.
... Consequently, the secondary stage, which is the most important part of the creep curve, improved because of the appearance of viscoelasticity. This characteristic, which is based on the properties of the specimen, determines the predestined lifetime of components [12]. The Maxwell and Kelvin model [11] may be the simplest viscoelastic model used to predict creep strain over time. ...
The creep test is one of the important approaches to determining some mechanical properties of composite materials. This study was carried out to investigate the creep behaviour of an epoxy composite material that was reinforced with Y 2 O 3 powder at weight ratios of 2%, 7%, 12%, 17% and 22%. Each volume ratio was subjected to five loads over the range of 1N to5N at a constant temperature of 16 ± 2°C. In this work, creep behaviour, stress and elasticity modulus were studied through experimental and numerical analyses. Results showed that increasing the weight ratio of Y 2 O 3 powder enhanced creep characteristics.
... However, this implied that as the fiber weight increases, Entada mannii fibers have prospects to absorbed moisture contents after chemical treatment causing incomplete dissolution of hemicellulose and intensify cellulose contents [39,40]. Additionally, after treatment fiber surface is exposed, fibrillar structure was altered causing poor fibermatrix interfacial adhesion under wet conditions as compared to pure PP [41]. A saturation point was attained after 10 days of immersion for both NaOH treated and pure PP. ...
This study evaluates the water diffusion mechanism on mechanical properties of polypropylene reinforced composites. Compounding of the composites into sheets was carried out using the compression moulding techniques by incorporating varying weight percentage of fibers and polypropylene. Mechanical properties of the composites were assessed according to ASTM standards, while the composite fracture surface was examined using a scanning electron microscope. The water absorption behaviour and diffusion mechanisms on mechanical properties of fabricated composites were analysed using a water immersion test and the Fickian diffusion model. The results show that mechanical properties of all polypropylene reinforced composites under dry condition was higher than wet condition. The composites reinforced with 7 wt.% (KOH and NaOH) fibers follow a consistent trend and gave the highest tensile strength and tensile modulus in comparison with pure PP (polypropylene). Addition of fibers into the polypropylene matrix gradually decreases composites impact strength with exception to 3 wt.% and 5 wt.% composites. The hardness properties of reinforced composites were steadily increased as the fiber loading increases which signify strong fiber-matrix bonding. The percentage of water absorbed for all reinforced composites increased as the fiber weight increases and slowly flattened off after 10 days of saturation. The morphological study revealed fiber pullout and delamination of reinforced composites attributed to poor fiber-matrix adhesion amount to water intake. The diffusion transport mechanism of polypropylene composites was observed to obey the Fickian diffusion model.
... Further increase in wood weight ratio resulted in poor bonding between the matrix and fiber. Facca and Andrzej achieved the same trends [25,26]. The composites exhibited a positive result when parameters C and D were increased for the entire chosen level due to increase in the contact area between the fiber and matrix as fiber content increased. ...
At present, composites are being utilized on account of simplicity in manufacturing and their characteristics are low weight, non-abrasive, non-flammable and non-harmful. This article attempts to achieve good mechanical properties of the wood and woven jute based natural fiber-reinforced plastics. The required composite materials were fabricated by using a hand layup method. The fabricated laminates were immersed in liquid nitrogen at 77 K for cryogenic treatments. The following parameters are (i) wood density, (ii) wood weight ratio, (iii) woven jute type, (iv) number of jute layers, (v) cryogenic treatment durations and (vi) alkaline treatment durations, each at three different levels were picked for composite development by utilizing the Gray-Taguchi method. Mechanical testing of fabricated laminates was done as per ASTM standards to estimate compressive, double shear and hardness properties. Based on the L 27 (3 ⁶ ) orthogonal array of the Grey Taguchi technique, 27 investigational trials were conducted. According to the Gray relation analysis, 300 kg m ⁻³ of wood density with a weight ratio of 12%, three layers of 350 gsm woven jute, 60 min of cryogenic treatment and 4 h of alkaline treatments resulted in good mechanical strength of the composites. Based on the Analysis of Variance, wood density was identified as the most influencing parameter that contribute up to 35.65% to the improvement of the mechanical strength of hybrid composites. The morphological expositions of NaOH treated hybrid composites and degree of fibers’ dispersion into the matrix were discussed based on Optical and SEM images.
... For example, Chattopadhyay et al. used maleic anhydride-grafted-polypropylene (MA-g-PP) as a compatibilizer for alkali treated short bamboo fibers reinforced PP composites to improve fibre-matrix interfacial adhesion [19]. Another procedure employed to improve interfacial adhesion to enhance mechanical properties even further has involved the treatment of fibers with compatibilizer prior to processing [20,21]. An in-depth review of various natural fibers and their composites by James et al. studied different selection procedure, preparation process and comparisons of properties [22]. ...
Polypropylene (PP) composites were prepared by incorporating short bamboo fiber (SBF) and treated hollow glass microspheres (HGM) and their thermal, thermo-mechanical and water absorption behaviour were analysed. Hybrid composite showed a higher glass transition (Tg) and crystallization temperature (Tc) compared to PP while insignificant effect on melting temperature (Tm) was observed. Significantly lower percentage crystallinity (%Xc) was observed for the hybrid composite in comparison to PP. Thermogravimetric analysis depicts that hybrid composite offers a thermal stability in vicinities of PP demonstrating that HGMs duly compensate the decrease in stability due to SBF addition. Storage modulus, and hence, stiffness of hybrid composite was greater than both virgin PP and composites with single reinforcer/filler. It is also apparent from loss tangent results that addition of HGM increased the damping more as compared to equal SBF addition. Water absorption results reveal that although hydrophilic SBF is responsible for higher moisture absorption and diffusivities, HGM addition reduces water penetration by partially shielding SBF, hence enabling improved hybrid swelling behaviour.
... However, the creep properties of the resin matrix limit the application of WPC in load-bearing structures [11][12][13]. To use WPC in a long-term load structure, creep and creep rupture (time-dependent failure) have to be overcome [14]. ...
Coextruded composites (CEC) with a core-shell structure were manufactured, with laminated veneer lumber (LVL) as the core layer and wood-plastic composites (WPC) as the shell layer. The creep responses of the LVL and CEC at stress levels of 30%, 40%, and 50% of ultimate flexural strength at room temperature were determined using the three-point bending test. The creep parameters of the CEC and LVL were determined by in-house creep testing. The first derivative of creep strain results indicated that the creep performance of the CEC was more stable than that of the separate LVL in an unstable external environment. Three different widely known creep models in the literature, including the Burger model, Findley power law model, and Bailey-Norton model, were used to model the creep behavior of LVL and CEC in this study. The correlation coefficients of all nonlinear fitting curves exceeded 0.9, while the predicted values of the Burger model and Bailey-Norton model were deviated from the experimental values in the later stage of experiment. The creep formula for the LVL and CEC obtained based on the Findley model can be used to predict their long-term creep behavior. These findings have increased the selection range of environmentally friendly load-bearing materials that can be adapted to hot and humid environments, as well as the application of WPC and LVL.
... In addition, raising the concentration of fibers has been proved to enhance the creep resistance of polymer composites to some extent. 31 As shown in Figure 5, the value of order is relatively smaller when more fibers are added into the polymeric matrix. Figure 8 shows the values of parameters a and b with different fiber contents, and it is observed that the values of both parameters a and b are decreasing with increasing fiber content. ...
To describe the creep behavior of natural fiber/polymer composites (NFPCs), a novel variable fractional order creep model is proposed in this work. With experimental data of polymer composites obtained from creep tests at different temperatures and with different fiber content, the effectiveness of the proposed model has been demonstrated. With the advantage of only four parameters, the variable order creep model is proved to give accurate descriptions on the creep behaviors of polymer composites by comparing simulated results with experimental data. Furthermore, a parameter study is conducted, which reveals the physical significance of model parameters. It is observed that the order increases linearly with time, which demonstrates the polymer composites softened during creep. Analysis of order indicates that high temperatures can activate the softening of the materials and the variable order is able to depict the change of microstructures of polymer composites. Besides, the relations between fiber content and order curves provide new perspectives on manufacturing NFPCs. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2020, 137, 48796.
... Properties like tensile and flexural were also enhanced when recycled polypropylene was used with WF and glass fiber mat. It has also been seen that compatibility of WF and glass fiber increased as the WF content increased [67][68][69]. Mesh size of WF also have significant effect on mechanical properties of composite. With 40 phr mesh size of WF, the composite exhibit better tensile and flexural strength. ...
The present paper deals with the examination of mechanical and tribological behavior of glass fiber reinforced epoxy composite. Wood flour (WF) is added as filler in glass fiber (GF) and epoxy matrix
material for the fabrication of composites. The Percentage ofWFis varied from 2.5 wt% to 10 wt% keeping the glass fiber constant. The mechanical properties, water absorption and tribological behavior of fabricated composites evaluated. It was found that water uptake increases as the percentage ofWFin the composite increases i.e. from 2.5 wt% to 10 wt% and it was least for neat GF reinforced epoxy composite. The composite ofWF wt% of 7.5, absorb maximum energy and exhibited maximum strength. Moreover the wear rate increases as the percentage ofWFin the composite increases. Present investigation also deals with the design of experiment (DOE). TheDOEwas carried
out with the help of TOPSIS for the qualitative analysis and the ranking was done according to the order of preference.
... At moisture contents greater than about 20%, fungal decay may occur (Christensen and Kaufmann 1965). Furthermore, exposure to fluctuating moisture conditions within the range 0 to 30% resulted in dimensional instability which can cause distortion of wood components in building (Bledzki and Faruk 2004). To improve dimensional stability and to reduce the probability of fungal attack it is desirable to restrict the entry of water into wood. ...
Due to its origins, wood remains biodegradable and needs to be protected against abiotic and biotic agents for a long service life. Tannin-boron associations can be considered as an innovative preservative formulation and environmentally-friendly treatment. These waterborne associations of tannins and boric acid increase the permanence of boron in the wood. Furthermore, boric acid is partly fixed to the network of autocondensed tannin in the wood and keeps sufficient mobility to maintain its biological action. These associations have been investigated for their outdoor applications, both above and in-ground, as well as for their ability for fire protection. An original formulation of tannin-hexamine and boric acid, has shown efficiency against biological attack and fire degradation. The natural and artificial weathering behaviour, and laboratory scale leaching, of such treated wood have been investigated, and followed by biological tests. The results showed that the weatherings led to different performances, always linked with the amount of remaining boron. An advanced tannin-boron formulation including ɛ-caprolactam to make the polymer network more flexible (and avoiding cracks as noticed for the original formulation) was studied for the chemical mechanisms, biological resistance above and in-ground, fire retardancy. The tannin polymer acquires a more elastic structure after adding ɛ-caprolactam, as seen with FT-IR analyses. The biological resistance of the treated wood provided a long lasting protection against degradation in outdoor exposures, and even in ground contact. However, fire retardant effect of this advanced tannin-boron preservative was negatively influenced with comparison to the original tannin-boron formulation, but still better than control. In order to improve the associations between boron and tannin for wood protection, the conception of wood polymer nanocomposite using tannin, boric acid and montmorillonite tentatively carried out. The analyses of FT-IR and XRD have investigated to identify nanoclay in Wood Tannin Nanocomposite (WTNC). Meanwhile, the trace of montmorillonite in wood cell is also captured by SEM. By comparison with control, compression strengths of WTNC samples increase; water absorption and gluing ability of WTNC depend on the wood species used (Scot Pine vs. Beech); dimensional stability of WTNC is slightly decreased, and wettability was significantly decreased. Fungal and termite resistance of WTNC are improved to different extends if Scots pine or beech samples are used. Fire performances of WTNC is affected differently depending on the wood species used and the parameters considered. This study also analyses the environmental impacts of producing tannin-boron (TB) preservative (the original formulation) and comparatively introduces the cradle-to-grave life cycle environmental impacts (LCA) of TB-treated timber as landscaping materials, compared with 2 industrial formulations and concrete.Even if all these tannin-boron association systems developed still need to be improved for some point of their chemistry, biological performances (coleoptera insects, field tests with termites, molds…), as well as for their eco-toxicological profile, they have shown to improve the biological and fire resistance of the wood.
... The coupling agent itself, malleated PE copolymer, contains nonpolar PE backbone and polar maleic anhydride groups. The interaction between the wood and PE matrix was caused by two effects; the chemical bonding interaction between the hydroxyl groups in cellulose and anhydride groups in the coupling agent in addition to the entanglement between the nonpolar PE matrix and nonpolar PE chains in the coupling agent, 48 as schematically shown in figure 2. ...
This work aims to improve the adhesive force of epoxy coating with a wood-plastic composite (WPC) surface. First, WPC was formulated using the extrusion technique through different percentages of wood flour (WF) with virgin polyethylene (PE) in the presence of a coupling agent. Dynamic mechanical analysis and water percentage gain (WPG%) were performed to find the optimized WF/PE mixing ratio. The optimized formula was subjected to surface treatment by different methods, including chromic acid oxidation, ultraviolet irradiation, and flame and heat treatment. Then the treated surface of WPC was coated with nano-modified epoxy resin using carboxylated carbon nanotube, organically modified nanoclay (Cloisite-30B), and reactive rubber nanoparticles. The surface treatment of the WPC was characterized with contact angle measurement and Fourier Transform Infrared (FTIR), while the interaction between the WPC and epoxy coat was investigated by attenuated total reflection FTIR microscopy analysis. The adhesion strength of the nano-modified epoxy showed significant enhancement when investigated by pull-off method and cross-cut test. Nano-scratching was utilized in exploring the effect of different surface treatments on enhancing adhesion to epoxy. The interfacial morphological behavior of epoxy coating on the WPC surface was investigated by Scanning Electron Microscope. The results indicated that chemical treatments helped for the functionalization of the WPC surface, leading to stronger adhesion with epoxy. These epoxy-coated WPC composites recorded enhanced mechanical properties because of the chemical reaction between the WPC surface and epoxy.
... 27 Creep modulus of wood fiber polypropylene (PP) composites at different temperatures (Bledzki and Faruk[56]). ...
This chapter focuses on mechanical performance of biofibers such as flax, hemp, and sisal and their effect on mechanical performance when they are reinforced in thermoset and thermoplastic polymers. The aim of this chapter is to present an overview of the mechanical characterization of the biofibers and their corresponding composites. The mechanical characterization includes tensile, flexural, impact, compressive, shear, toughness, hardness, brittleness, ductility, creep, fatigue, and dynamic mechanical analyses. Detailed studies of each test have been widely reported and an overview is important to relate the studies. Studies pertaining to the topics are cited. The most common materials used in biocomposites are biofibers (also called natural fibers) and petroleum-based polymers such polypropylene. The use of renewable materials in biocomposites has increased in the past couple of decades owing to extensive research on cellulosic fibers and biopolymers based on starch or vegetable oil. Today, research is focused on reinforcing natural fibers in petroleum-based polymers. However, the emphasis is shifting toward the amount of renewable materials in biocomposites, which has led to the use of biopolymers instead of petroleum-based polymers in composites. The mechanical properties of some renewable resource-based composites are comparable to commercially available nonrenewable composites.
Several plant biofibers have been reinforced in thermoplastics or thermosets to manufacture biocomposites because of their specific properties. The Young's modulus of commonly used biofibers such as hemp and flax could be over 50 GPa and therefore they could be good alternatives to glass fibers in several applications. The good mechanical properties of these biofibers influence the composites' mechanical performance when reinforced in polymers. It is important to understand the mechanical performance of these biofibers and biocomposites in a working environment. A detailed discussion about the mechanical performance of commonly used biofibers and composites is provided in this chapter.
... Therefore, the creep properties of CW/HDPE were poorer than the HW/HDPE and the HW/HDPE. Moreover, the well-dispersed fillers in the matrix were beneficial for stress transfer, which resulted in reduced deformation [32]. The aggregation of AL-RS had unfavorable effects on its dispersion in the HDPE matrix, which could be the reason why the creep behavior of AL/HDPE was worse than that of HW/HDPE. ...
The removal of rice straw extractives increases the interphase adhesion between rice straw and the high-density polyethylene (HDPE) matrix, while eradicating the inner defects of rice straw/HDPE composites. This study investigated the effect of rice straw extractives removal on the dimensional stability (water uptake and thermal expansion), dynamic mechanical properties, creep, and stress relaxation of rice straw/HDPE composites. Cold water (CW), hot water (HW), and 1% alkaline solution (AL) extraction methods were utilized to remove rice straw extractives. Extracted and unextracted rice straws were mixed with HDPE, maleated polyethylene (MAPE), and Polyethylene wax to prepare composites via extrusion. Removal of rice straw extractives significantly improved the dimensional stability, dynamic mechanical properties, and creep and stress relaxation of rice straw/HDPE composites, with the exception of the thickness swelling of the AL/HDPE and the thermal expansion of the rice straw/HDPE composites. HW/HDPE exhibited the best comprehensive performance.
Materials that are non-toxic and environmentally friendly become demandable due to lack of resources and augmented contamination of the environment. Plant fibre reinforced composites (PFRCs) have swapped synthetic fibre reinforced...
Polymer composites have gained immense popularity in various industrial applications owing to their excellent mechanical properties. However, their mechanical behavior under dynamic loading and creep recovery is not well understood, and their performance is influenced by various factors such as the type of polymer, reinforcement, and crosslinking. In this study, we provide an overview of the dynamic mechanical and creep recovery behavior of polymer composites and discuss the effects of crosslinking on their properties. Additionally, mathematical models have been developed to predict the mechanical behavior of polymer composites under different loading conditions. This chapter aims to provide a better understanding of the mechanical behavior of polymer composites and to enable the development of new and improved materials for various applications.
Cellulose-fibre-reinforced epoxy and vinyl-ester ecocomposites were fabricated in conjunction with inorganic nano-fillers. The effect of cellulose fibre and/or nano-filler dispersion on the mechanical properties of these composites has been characterized. The fracture surface morphology and toughness mechanisms were investigated by SEM. Results indicated that mechanical properties increased as a result of fibre and nano-filler additions. In particular, the presence of cellulose fibres significantly increased the mechanical properties of ecocomposites.KeywordsEcocompositesCellulose fibresNano-fillersNanocompositesMechanical propertiesFlexural strengthImpact strengthFracture toughnessImpact toughness
Due to the sustainable, and commercial outcomes of the natural fibers, along with their desired features such as high specific mechanical properties, natural fiber-reinforced composites (NFRCs) are exhibiting a strong potential to be employed in different applications such as aerospace, automotive, packaging, etc. This chapter presents a comprehensive discussion on the main characteristics of seawater ageing and moisture ingress mechanism influencing natural fibers and their performance as reinforcement in polymer matrix composites. This chapter presents the influence of seawater ageing on the physical and mechanical properties of NFRCs. Furthermore, the chapter also discuss various measures to prevent moisture ingress. Many researchers have been focusing attention to overcome the issues due to moisture absorption, with particular interest paid to the physical and chemical treatment of reinforcements and improving the fibre–matrix interface strength. Recent studies and developments dealing with moisture repellent coatings are also discussed.
KeywordsNatural-fiber reinforced composites (NFRCs)Moisture absorptionAgeingMechanical and thermal propertiesChemical and physical treatmentsCoatings
Arecanut leaf sheath (ANLS) an unexplored agricultural biomass is used to recover long staple lignocellulosic fibers. A long staple lignocellulosic fiber is extracted from ANLS biomass using 8% NaOH treatment. As reinforcing material ANLS fibre properties such as fibre length, diameter, moisture content, single fibre strength and X-ray diffraction analysis were carried out. Three types of composites, 15, 20 and 25 (w/w)% fibre loading composites have been prepared in unsaturated polyester resin matrix. The tensile, flexural and interlaminar shear strength (ILSS) properties and void content of these composites are studied. The tensile fracture behaviors of fibre and composites are studied with the help of scanning electron micrographs.
The study's main motivation is to determine the creep behavior of high‐density polyethylene (HDPE)‐based nanocomposites in unexpected situations where short‐term constant loading may occur. On this basis, the short‐term creep behavior of 1 wt.%, 3 wt.%, and 5 wt.% nanoclay reinforced HDPE nanocomposites were investigated at room temperature (23 ± 1°C) and strain rate of 1E‐4 1/s under 8, 12, and 16 MPa stress levels. As the nanoclay reinforcement ratio by weight increased, the creep resistance and modulus of neat HDPE increased at 8 MPa stress level, but they decreased at 12 and 16 MPa stress levels. The absorbed energy that corresponds to the area under the stress–strain curve increase as the stress level increase from 8 to 16 MPa. However, absorbed energy decreases as nanoclay reinforcement increases for 8 MPa. The curves produced from the four‐element Burger's model and Findley's power law models were compared with the creep curves obtained from the experiments. The four‐element Burger model was found to fit the creep curves better than Findley's power‐law model. Also, some regression curves were given for interpolations to give intermediate values of the maximum creep strain values at different stress levels. The presented models can be used to evaluate creep strain, considering the usage fields of parts or semi‐products produced from nanoclay/HDPE nanocomposites.
Present day biocomposites have been developed in such a way that their properties are comparable to the properties of commercially available nonrenewable composites. These biocomposites are manufactured using biofibers as reinforcements in the thermoplastic or thermoset resins. To understand the performance characteristics of these biocomposites, it is essential to predict their material characterization under different specific environmental conditions. This chapter provides a detailed discussion on the various mechanical and physicochemical characteristics of the biobased fibers and composites. Chemical composition, density, morphology, and wettability are the properties studied during the physicochemical characterization. Tensile, flexural, impact, toughness, brittleness, and creep are the various mechanical properties elaborated in this chapter.
Luffa Cylindrica (LC) is the dried fruit of a sponge-type plant belonging to Curcubitacea family. Recent advancements in hierarchical and lightweight structures have aroused interest in this natural fibrous material for illustrating an extraordinary multiparous architecture of high anisotropy and low density. To the extent of its biodegradable nature, such a structure is potentially apt to replace conventional porous-like composites for low-energy absorbing and material reinforcing applications. In order to investigate its candidacy as a long-term sustainable reinforcement, a LC layer is impregnated with an epoxy resin (ER) system and subjected to tensile creep tests within the linear viscoelastic regime. Specimens loaded with 30% weight fraction of LC fibers are tested at four stress levels corresponding to 5%, 8%, 10% and 15% of the static tensile strength σu of the composite. The viscoelastic response of the LC/ER composite is found improved with respect to that of the pure polymer. This improvement is reflected to the creep strain and compliance that decreased by 30%. The creep results are subsequently probed by means of the four–parameter (Burger) analytical model to gain insight on the viscoelastic behavior.
This work computationally predicts the onset of moisture-induced damage for different wood polymer composite (WPC) formulations using an experimentally validated micromechanical model. For model validation, the flexural mechanical properties of a commercially available WPC were experimentally obtained after exposure to either moisture or combined moisture and freezing conditions. As expected, exposure caused a loss in mechanical properties, which was primarily attributed moisture-induced damage and not further exacerbated by freezing. Once validated, the model was used to predict that the WPC would incur damage when placed in a commonplace 40–45 % relative humidity environment. This work demonstrates that computational simulations can be used to design moisture-resistant WPC formulations given specific environmental conditions (i.e., relative humidity, temperature) of the intended target application.
The effect of strain rate on the mechanical properties of two epoxy adhesives was investigated by conducting experiments on dumbbell-shaped specimens prepared from the adhesives. The tensile rate was changed stepwise from 5.2 × 10–5 to 1.2 × 10⁶ mm/min, and the yield stress, Young’s modulus, elongation, and tensile strength were evaluated. The yield stress and tensile strength showed a clear dependence on the strain rate. The results from this study allowed us to propose a procedure for predicting the creep strength and high-rate impact strength from the results of a simple tensile test.
This paper is intended to investigate the effect of chemical treatment on the creep and recovery behavior of injection molded jute–polypropylene composites in flexural mode. The chemical treatment of short jute fibers was done using sodium hydroxide (NaOH), silane (SiH 4 ), potassium permanganate (KMnO 4 ), and the use of maleic anhydride (C 4 H 2 O 3 ) as a coupling agent. The effectiveness of the chemical treatments was initially studied by comparing the tensile and flexural properties, along with the scanning electron microscopy fractographs. The creep behavior of the composites was modeled using four-parameter Burger’s model and the same was compared with the classical power law model. To model the recovery behavior, Weibull distribution function was used. The correlation between model parameters and different chemical treatments has been emphasized. The time–temperature superposition principle was employed for predicting the long-term creep behavior of the chemically treated jute–polypropylene composites.
The characteristics of natural fiber reinforced composites such as light weight, non-abrasive, nonflammable, nontoxic, low cost and biodegradable have grabbed the attention of current researchers in the area of composites. The objective of this study is to examine the interlaminar shear strength of the polyester based wood and woven jute hybrid composite. To accomplish this objective, the following parameters such as (i) wood density, (ii) wood weight ratio, (iii) woven jute type, (iv) number of jute layers, (v) cryogenic treatment duration and (vi) alkaline treatment duration, each at three different levels were picked and optimized using the Taguchi method. The fibers were pretreated with 5% of NaOH solution for different length of time to reduce the moisture absorption. The L27 orthogonal array was selected for the chosen parameters and the required composite materials were fabricated using hand lay-up techniques. The fabricated composites were then subjected to cryogenic treatment by immersing in liquid nitrogen at 77 K for different period of time. The interlaminar shear strength of the fabricated hybrid composites was done according to ASTM standard. The morphological features and degree of dispersions of fibers into the matrix of the fabricated hybrid composites were further studied and discussed.
In presented research work, high energy planetary ball milling process was employed to prepare different types of organic and inorganic particles by dry pulverization. The agricultural fibrous waste (i.e. Agave Americana, cornhusk, jute) was utilized to prepare organic particulate fillers whereas the wastes of basalt, carbon, glass and fly ash were utilized to prepare inorganic particles. The particles were then incorporated at 3 wt% loading into epoxy resin, and their properties were investigated for improvement in dynamic mechanical and creep behavior of epoxy composites.
Renewable raw materials and sustainability has a widespread significance for all types
of industry. Cellulose, which has a great potential as a raw material for various branch of industry including
textile, is the main component of most vegetable fibers. Cellulose from different vegetable resources
can be isolated using chemical and mechanical treatments. Chemical treatments are effective for
delignification. Based on this, the aim of our study is extraction of sustainable cellulose from lignocellulosic
banana plant waste using chemical treatment. First, the waste banana plants were supplied
as resource of cellulose considering the previous works about this topic and preliminary experimental
studies. After that, the composition of the extract was determined in order to confirm the high cellulose
content. At the next stage of this study, organic acid extraction method was used to extract cellulose from
banana plant wastes. The cellulose content of banana plant was determined as 57% and 24%
of hemicellulose. The cellulose was successfully extracted from banana plant wastes. Characterization
results suggest that cellulose, an important raw material for textile, pulp and paper, composite and defense
industries, can be effectively regained from banana plant wastes.
Keywords: Cellulose, extraction, banana plant wastes, pulping.
Nonlinear creep behavior of one commercial short glass fiber reinforced polypropylene was investigated using tensile creep tests and stiffness degradation measurements. The impact of thermal aging and following quenching was evaluated on the latter mechanical property. Experimental results were modeled applying nonlinear viscoelastic model used by Pupure et al. (2013) and developed by Lou and Schapery [1,2]. Results showed that this model can describe nonlinear behavior of short glass fiber reinforced polymer composites, where microdamage is given by debonding of fiber-matrix interfaces already at low strains, where cracks propagate and lead to tensile creep fracture.
Using trihydroxy polyether polyol (PPG), diphenylmethane diisocyanate (MDI) as soft segment and hard segment, carbon fiber (CF) as reinforcement, and self‐crosslinking CF/polymethyl methacrylate (PMMA) composite was prepared by prepolymer method. In this study, starch and octanoyl chloride were esterified to obtain esterified starch (SE). The fiber is then melt blended with PMMA matrix to prepare PMMA composite. Fourier‐transform infrared spectroscopy (FTIR) and SEM were used to analyze and characterize the composites produced. The results show that the composite material was prepared by separately modifying the fiber with NaOH and SE, respectively. The mechanical properties of the composite materials prepared by the modified fiber are improved, and the fiber and the PMMA matrix showed better compatibility. The mechanism of comodified fiber enhanced the mechanical properties of its composites.
Improvements in the characteristic properties of jute-polypropylene composites were obtained with the application of MAH grafted PP copolymers as a coupling agent to the fiber. SEM investigations demonstrated that fiber pull-out is reduced after the modification with the coupling agent. This improved fiber-matrix adhesion further leads to a lower creep strain in the outer fibers. This was demonstrated for composites with two different fiber contents. Up to applied stresses of 5.1 N/mm2, the creep behavior for the composites with unmodified, as well as for those with MAH-PP modified, fibers obeys the creep law according to Abbott. The experimental data of creep tests at higher applied stresses were fitted more successfully by using the creep law according to Findley. The creep kinetic coefficient according to Abbott was dependent on the applied stress for both types of composites and for both fiber contents.
This paper deals with the impact behavior of natural fiber-reinforced epoxy foams. The effects of different types of fibers, fiber content and void content were discussed. It was found that the woven flax fiber results in composites with better impact strengths than the woven jute fiber based composites. The impact damage configuration and mechanism of these laminated composites were discussed. Impact properties such as loss energy and damping index were found to be almost linearly dependent on void content and impact energy. The loss energy and damping index were decreased with increasing fiber content under comparable void content and test conditions.
Wood polypropylene composites (WPC) of different compositions (30, 40, and 50%) have been prepared using maleic anhydride–polypropylene copolymer of different percentage (5 and 10% relative to their wood fiber content). Tensile, flexural, fracture toughness, and impact test of the prepared WPC were carried out. From the results, it is observed that the hard wood fiber–polypropylene composites, by using maleated polypropylene (MAH-PP), show comparatively better performance to soft wood fiber–polypropylene composites. Tensile strength and charpy impact strength have been increased to a maximum of 50 and 20%, respectively. The damping index has been decreased by 60% when 10% of MAH-PP has been used. Water absorption and scanning electron microscopy of the composites are also investigated.
Jute fiber-reinforced polypropylene composites have been produced and characterized in order to investigate the influence of water on their mechanical properties. Being hydrophilic, jute fibers absorb a high amount of water causing swelling of fibers. On the other hand, the thermal shrinkage of polypropylene melt leaves some gaps between jute fibers and matrix material. We investigated whether these gaps could be filled by the swelling of wetted fibers. The fillup of these gaps would result in a higher shear strength between fibers and matrix during fracture. Our results suggest that swelling of jute fibers in a composite material can have positive effects on mechanical properties. © 1994 John Wiley & Sons, Inc.
Two unsaturated polyester resins based on poly(1,2 propylene–maleate–phthalate) (PE1), and poly(oxy–diethylene–maleate–phthalate) (PE2) were used for the impregnation of oven-dried white pine wood samples in admixture with styrene (S). Curing was affected by the initiator-heat technique by either using 0.1–0.2% by weight of benzoyl peroxide (Bz2O2), or 1% by weight of methyl ethyl ketone peroxide (MEK). It was found that the use of PE1/S mixture resulted in the formation of wood–plastic combinations (wpc) with higher percent retention and higher percent polymer loadings than those obtained by the impregnation of wood samples with PE2/S imxtures. The use of different swelling solvents including ethanol, acetone or chloroform, did not influence the percent retention or polymer loadings of wpc for either PE1/S or PE2/S mixtures. Physical tests performed on wpc showed that compression, hardness, static bending were generally enhanced, water absorption was decreased, and dimensional change was retarded to different extents for both polyesters used, but no permanent stabilization was attained.
Utilization and conservation of raw materials are two of the main thrusts of our research. Several plasticized woods have been prepared from sawdust in our laboratory. They possess unique thermal, mechanical, and viscoelastic properties. In this study, benzylated wood was used to blend with polystyrene to prepare a wood/plastic composite. Its dynamic processability and viscoelastic properties were evaluated. The mixtures with different blending ratios (benzylated wood/polystyrene) were prepared by mixing them in an intensive mixing device. The specific energy required to do the processing work decreased with the increase of benzylated wood in the composite. The mixture can be molded or extruded easily. The study of the viscoelasticity of the compression-molded composite products using a dynamic mechanical thermal analyzer (DMTA) revealed, regardless of the mixing ratios, a single damping peak (tan δ). This suggested good compatibility between the two polymers. The glass transition temperature and the storage modulus of these composites decreased as the amount of benzylated wood increased. A composite with comparable mechanical properties of polystyrene was obtained from those composites with mixing ratios (benzylated wood/polystyrene) ranging from 0.4 to 0.6. © 1993 John Wiley & Sons, Inc.
Woodflour of Eucaliptus saligna with two different chemical treatments (mercerization and esterification with maleic anhydride) was used as filler of an unsaturated polyester matrix. Woodflour was treated to increase the interfacial adhesion with the matrix, to improve the dispersion of the particles, and to decrease the water sorption properties of the final composite. The objective of this study was to determine the influence of the moisture content and the woodflour chemical modification on the physical and mechanical properties of the different composites. Results indicated that mechanical properties (compression and bending tests) were severely affected by moisture and chemical modifications. In wet conditions, the composites made from treated woodflour had the lowest flexural modulus and ultimate stress. It was found that this was a reversible effect, because the original values of the compression properties were recovered after drying. Temperature scans in dynamic mechanical tests showed that an irreversible change occurred during exposure to humid environments, probably due to the hydrolysis of the polyester matrix. Essentially, the same behavior was observed for matrix and composites; however, a wood-related transition overlapped the main transition in the case of wet composites. © 1998 John Wiley & Sons, Inc. J Appl Polym Sci 68: 2069–2076, 1998
Short term flexural creep tests were conducted to investigate the creep behavior of wood-fiber polypropylene composites. Three experimental parameters were selected: the addition of a wetting agent, temperature, and wood-fiber concentration. All creep curves are presented in terms of relative creep as a percentage of instantaneous (initial) strain. The creep power law model was used to accurately fit the creep data. The addition of a wetting agent greatly reduced the creep at high stress, but had little effect at a lower stress level. The extent of relative creep increased with increasing temperature. It was found that the slope of the power law model was directly proportional to the temperature. The addition of wood-fibers into pure polymer greatly improved the creep resistance of the matrix polymer. The relative creep of the composites decreased with an increase in wood-fiber concentration. However, the composite showed relatively large creep compared with that of solid wood. It was found that both the time exponent and slope of the power law model were inversely related to wood-fiber concentration. The flexural modulus of the composites also had an inverse relationship with the time exponent.
Wood–polymer composites (WPC) of Geronggang (GE; Cratoxylon arborescens), a light tropical hardwood, impregnated with methyl methacrylate (MMA) and styrene-co-acrylonitrile (3 : 2; STAN), were prepared by in situ polymerization using γ radiation or catalystheat treatment. The dynamic flexural storage modulus, E′, for oven-dried GE, moist GE, and GE–MMA and GE–STAN composites decreased with increasing temperature. The percentage decreases for GE with 10 and 16.5% moisture contents were 74.5 and 98.2%, respectively, which were higher than those for GE and GE composites, which ranged between 40 and 50%. The impregnated polymers were not as effective as water in acting as plasticizers, due to their nonpolar nature and much higher molecular weights. The α-transition peaks for moist GE and GE composites were more distinct and were shifted to lower temperatures than those for oven-dried GE. The values ranged between 75 and 150°C for moist GE and between 102 and 170°C for the GE composites. The α-transitions of the catalyst–heat-treated GE composites were lower than that of the radiation-induced counterparts. GE–STAN composites were also observed to have lower α-transition temperatures than those for GE–MMA for the respective treatment process, which seems to suggest that STAN interacted to a greater extent with cell wall components than did MMA.
The performance of phthalic anhydride used as a coupling agent in wood fiber-filled polystyrene composites have been verified by evaluating the mechanical properties of the composites materials. Generally, mechanical properties improved along with the increase in concentrations of the coupling agent as well as wood fiber in the composites up to a certain limit and then decreased at the higher concentrations. The concentrations of phthalic anhydride and fibers which produce maximum improvements in mechanical properties differ with the change in wood species and pulping techniques. Compared to other efficient coupling agents (e.g., isocyanate), phathlic anhydride's performance seemed inferior.
Cellulose fibers were surface modified with polypropylene–maleic anhydride copolymer. The physical properties of such fibers were characterized by contact angle measurements, and the chemical structure was identified with ESCA and FTIR. ESCA showed that the modifying agent was localized at the surface of the fibers. The modified fibers were compounded with polypropylene, and composites with various amount of fibers were manufactured by injection molding. All mechanical properties were improved when treated fibers were used. SEM showed improved dispersion, wetting of fibers, and adhesion. The nature of adhesion was studied using FTIR. It was found that the surface modifying agent is covalently bonded to the fibers through esterification. The degree of esterification is enhanced by activating the modifying agent before fiber treatment. This study has shown the effects of treatment conditions on activation of reactive species and chemical reaction between fiber and modifying agent. Moreover, a better understanding has been achieved of the nature of adhesion for the system.
Cellulose fibers were grafted with compatibilizing agents, such as maleated polypropylenes of different molecular weights. Steric effects and surface free-energy effects were found to stimulate the stretching of grafted chains away from the cellulose fiber surface, giving rise to a brushlike configuration in a polypropylene (PP) melt. Inverse gas chromatography measurements on modified fibers using a model compound for PP as adsorbate showed that interactions of PP and grafted fibers, which were mainly diffusion-dependent, increased with increasing molecular weight of the compatibilizer. Dynamic mechanical measurements and tensile testing of composites showed that the presence of compatibilizing agents enhanced stress transfer and increased interphase thickness considerably, the most significant effect being obtained for the high molecular weight compatibilizers. Apparently, the longer the grafted chains, the larger the fraction of matrix molecules involved in the interactions and, thus, the thicker the interphase. The improvement of adhesion between treated fibers and PP, as detected by peel testing, was proven to be caused mainly by entanglements formed between compatibilizing agents and PP. © 1993 John Wiley & Sons, Inc.
Short pineapple-leaf-fiber-(PALF)-reinforced low-density polyethylene (LDPE) composites were prepared by melt-mixing and solution-mixing methods. In the melt-mixing technique, a mixing time of 6 min, rotor speed of 60 rpm, and mixing temperature of 130°C were found to be the optimum conditions. Tensile properties of melt-mixed and solution-mixed composites were compared. Solution-mixed composites showed better properties than melt-mixed composites. The influence of fiber length, fiber loading, and orientation on the mechanical properties has also been evaluated. Fiber breakage and damage during processing were analyzed from fiber distribution curve and optical and scanning electron micrographs. Considering the overall mechanical properties and processability characteristics, fiber lenght of 6 mm was found to be the optimum length of pineapple leaf fiber for the reinforcement in LDPE. The mechanical properties were found to be enhanced and elongation at break reduced with increasing fiber loading. Longitudinally oriented composites showed better properties than randomly and transversely oriented composites. Recyclability of the composite was found to be very good. A comparison of the properties of the PALF-reinforced LDPE composites with those of other cellulose-fiber-reinforced LDPE systems indicated superior performance of the PALF–LDPE composites.© 1995 John Wiley & Sons. Inc.
The influence of water environment on the sorption characteristics of low-density polyethylene composites reinforced with short pineapple-leaf fibers (PALF/LDPE) has been studied by immersion in distilled water at 28, 50 and 70°C. The effects of fiber loading, temperature and chemical treatment on the sorption behavior are also evaluated. Water uptake is found to increase with fiber loading owing to the increased cellulose content. Weight change profiles for the composites at high temperature indicated that the diffusion is close to Fickian. All of the treated composites showed lower uptake than the unmodified composites. Parameters like diffusion, sorption and permeability coefficients were determined and activation energies were calculated. The thermodynamic constants such as entropy, enthalpy and first-order kinetic rate constant have been evaluated. A correlation between theoretical and experimental sorption results was evaluated. The effect of water uptake on uniaxial tensile properties has also been studied. Mechanical properties decreased after exposure to water, depending on time of immersion, fiber loading and chemical treatment. Finally, studies were carried out on the flexural properties of PALF/LDPE composites exposed to ultraviolet radiation.
Impact resistance of long wood fibre–PP composites at differ-ent relative humidity atmospheres
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Fig. 8. Impact resistance of long wood fibre–PP composites at differ-ent relative humidity atmospheres (wood fibre content 60 wt.%).
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Effects of environment on Fig. 15. Creep strength of hard wood fibre–PP composites with compatibiliser at different temperatures after 180 min deformation
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Fig. 15. Creep strength of hard wood fibre–PP composites with compatibiliser at different temperatures after 180 min deformation.