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Poly (lactic acid)/modified gum arabic based bionanocomposite films: Thermal degradation kinetics
... Gum arabic (GA) is a natural polysaccharide which mainly consists of arabinose, glucuronic acid, rhamnose, galactose and proteinaceous molecules, obtained from exudates of Acacia Seyal and Senegal trees [4,5]. The GA can be divided into three major fractions: (1) arabinogalactan (2) arabinogalactan-protein (3) and glycoprotein (GP) which contain different protein contents (%) and molecular masses. ...
... It has been widely utilized in various applications such as pharmaceutical, cosmetics and food industry etc. It is also reported that, by using in situ polymerization to modify chemical structure of GA attaching some other hydrophobic polymer as a side chain, it may be possible to utilize in food packaging applications [4]. Such modifications are not only helpful to promote the growth of bioplastics at commercial level but also encourage the depletion of petroleum-based commodity plastics. ...
... In addition, -CH deformation band and C-OH side group vibration are also appeared at 1382 and 1041 cm -1 , while IR peaks at 1210, 1127 and 1092 cm -1 are associated with -C-O-C stretching. The main characteristic features are the transmission bands at 3300 cm -1 (ascribed for amino group which masked by -OH stretching), a sharp band at 1600 cm -1 (assigned for -N-H bending and -C=O stretching) and weak band at 2934 cm -1 (corresponding to -C-H stretching) for GA, which was reported by Tripathi et al. [4,15]. In case of fG, a band at 3484 cm -1 of the -OH band of OLLA group is shifted to 3526 cm -1 which confirms the functionalization phenomena. ...
The effect of functionalized gum arabic (fG) on the thermal decomposition behaviour of poly(lactic acid) (PLA) in the presence of dicumyl peroxide (DCP) is investigated from the thermogravimetric analysis (TG) and coupled TG–Fourier transform infrared spectroscopy (FTIR) techniques. A series of fG-grafted PLA film in the presence of DCP are facilely fabricated using reactive extrusion at a set processing parameters, i.e. temperature and speed of screw are maintained at 180 °C and 60 rpm, respectively. As compared to PLA, thermal stability is reduced with the increase in the fG content. The addition of DCP could assist to maintain the thermal stability of PLA-1fG-based biocomposites. The activation energy (Ea) is evaluated using the model-free approach, i.e. (1) modified Coats–Redfern (CR), (2) Flynn Wall Ozawa (FWO) and (3) Kissinger method rely on a set of dynamical TG experiments. The value of Ea determined using Kissinger method is 158 (PLA), 143 (PLA-1fG), 125 (PLA-3fG), 154 (PLA-D-1fG) and 140 kJ mol⁻¹ (PLA-D-3fG), respectively. Generalized kinetic plots suggest that mechanism change A2 (2D nucleation and growth) to R3 (3D phase boundary controlled reaction) for PLA, PLA-1fG, shift A2–A4 (4D nucleation and growth) for PLA-3fG and A2–R2 (2D phase boundary controlled reaction) in case of DCP-treated PLA-fG biocomposites. The releases of decomposed products for gum arabic, fG, PLA-fG-based reactive biocomposite are investigated using TG–FTIR technique.
... Most of these plastics are specifically targeted towards packaging applications since they undergo degradation during composting ( Arrieta et al., 2014 ;Ge et al., 2016 ;Narancic et al., 2018 ). It has been observed that biopolymers such as cellulose ( Dhar et al., 2016 ), chitosan ( Pal and Katiyar, 2016a ), gums ( Tripathi and Katiyar, 2017 ), when dispersed in PLA, can enhance certain required properties for food packaging. Studies show that cellulose nanocrystal (CNC), one of the most abundantly available biopolymer, can significantly improve the thermo-mechanical properties of PLA based composites ( Bitinis et al., 2013 ). ...
... Most biopolymers are hydrophilic in nature, but certain grafting techniques can be applied to change their surface properties from hydrophilic to hydrophobic. Accordingly, chitosan and gum arabic have been applied as the reinforcing phase for improving gas barrier properties of PLA films for food packaging applications ( Pal and Katiyar, 2016b ;Tripathi and Katiyar, 2017 ). However, these improved modified composite films must meet certain criteria regarding biodegradability, like 90% organic carbon present in the composite film must be converted to CO 2 , water, etc., under either compost or soil, following certain standards. ...
This study demonstrates the kinetics of aerobic biodegradation of melt-extruded poly(lactic acid) (PLA) based biocomposite films by online monitoring of CO2 using gas chromatography technique following ASTM International D 5338-15 protocol. Biodegradation studies of PLA and its biocomposites were carried out in the presence of compost microbes, without the addition of any external inoculum. The first-order kinetics model was modified by incorporating a linear lag phase for each test sample. Bacterial identification by 16S rRNA gene sequencing showed Bacillus flexus as one of the microbes responsible for biodegradation of the exposed films at thermophilic temperatures. Neat PLA (NPLA) and PLA/Chitosan composite films were found to evolve high amounts of C–CO2 (carbon-to-carbon dioxide). C–CO2 conversion was found to be very low in PLA/cellulose nanocrystals and PLA/gum arabic biocomposites, expressing the presence of only 4% and 6% slowly hydrolysable carbon, respectively, as compared to NPLA and PLA/chitosan samples. The C-CO2 evolution rate was the highest for PLA/chitosan sample at 1.13 day⁻¹. Experimental data of all the test samples showed a good fit (R² ∼ 99.99) with the kinetic model. Morphological analysis by FESEM confirmed the erosion of polymer during composting.
... Typical biodegradable polymer poly (lactic acid) (PLA) belongs to the chemical synthesis class, which can be prepared by ring-opening polymerization of lactide ( Figure 1) or direct condensation polymerization of lactic acid ( Figure 2) [11]. PLA has the characteristics of excellent degradation [12], biocompatibility, nontoxicity [13], and good workability and thermoplasticity among others [14]. PLA can be conveniently processed into thin films, fibers or molding parts [15]. ...
With the depletion of petroleum energy, the possibility of prices of petroleum-based materials increasing, and increased environmental awareness, biodegradable materials as a kind of green alternative have attracted more and more research attention. In this context, poly (lactic acid) has shown a unique combination of properties such as nontoxicity, biodegradability, biocompatibility, and good workability. However, examples of its known drawbacks include poor tensile strength, low elongation at break, poor thermal properties, and low crystallization rate. Lignocellulosic materials such as lignin and cellulose have excellent biodegradability and mechanical properties. Compounding such biomass components with poly (lactic acid) is expected to prepare green composite materials with improved properties of poly (lactic acid). This paper is aimed at summarizing the research progress of modification of poly (lactic acid) with lignin and cellulose made in in recent years, with emphasis on effects of lignin and cellulose on mechanical properties, thermal stability and crystallinity on poly (lactic acid) composite materials. Development of poly (lactic acid) composite materials in this respect is forecasted.
... The approximation pðxÞ≌ e −x x 2 utilized to solve the Eq. (5), which reliable for (20 ≤ x ≤ 60) [21,22]. ...
Systematic kinetics of melt-blended Poly(lactic acid) (PLA)/Poly(butylene succinate) (PBS) and PLA/PBS/functionalized chitosan (FCH) nanobiocomposites with dicumyl peroxide (DCP) and chemical changes thereof at degradation temperatures are evaluated using thermogravimetry (TGA) and thermogravimetry coupled to Fourier transform infrared spectroscopy (TGA-FTIR). A comprehensive kinetic model is employed on above blended samples, including (i) Flynn-Wall-Ozawa, Kissinger, Kissinger-Akahira-Sunose methods to investigate the kinetic and thermodynamic variables, and (ii) Generalized master plots to propose the thermal-induced mechanism. The thermal stability of PLA/PBS reduced with increasing FCH loading up to 3 wt%, and improved for DCP treated PLA/PBS/1FCH at maximum degradation temperature (Tmax) is noticed. The activation energy estimated from Flynn-Wall-Ozawa method are (129-139 kJmol-1), (116-152 kJmol-1), (109-146 kJmol-1), (132-169 kJmol-1) and (120-166 kJmol-1) for PLA/PBS, PLA/PBS/1FCH, PLA/PBS/3FCH, PLA/PBS/1DFCH and PLA/PBS/3DFCH respectively. The generalized master plots depicts that the PLA/PBS blend exhibited L2-F1 mechanism whereas their nanobiocomposite with or without DCP followed L2-Dn and A2-L2-Dn mechanism respectively. Coupled TGA-FTIR highlights the similar kinds of products such as lactide, acetaldehyde, esters, CO2 and CO liberated during the thermal degradation of PLA/PBS blend and their nanobiocomposites. These crosslinked/branched structures are postulated by the rheological behavior which confirmed increase in the complex viscosity (η*) and storage modulus (G') of PLA/PBS/D/1FCH.
... structure of MG [46]. Other characteristic peaks are observed around ~1045 cm -1 and ~1595 cm -1 indicating -OH stretching and -C=O stretching as well as -N-Hbending, respectively [47]. ...
The article demonstrates a simple and innocuous method for fabrication of poly (lactic acid) (PLA)/modified gum arabic (MG)based hydrophobic, microcellular, highly porous and interconnected composite foam. The observed density of the composite foams was remarkably reduced by ~86% in comparison to PLA granules. Further, there was noticed an increase in cell density and a decrease in cell size due to the addition of MG nanofiller. The thermogravimetric analysis (TGA) of developed foam showed no significant effect of MG in maximum degradation temperature (Tmax). Dynamic mechanical analysis (DMA) and differential scanning calorimetry (DSC) investigations suggested the plasticizing effect of MG nanofiller in the PLA matrix. The hydrophobicity of fabricated foam was found to increase with an increase in loading of MG and an increment of ~20° in contact angle was observed for highest loading of MG (3%) in comparison to neat PLA foam. Further, an increase in the surface area up to ~60% and a decrease in pore diameter up to ~53% were observed for PLA/MG based foam by porosimetric investigations. Based on this investigation, the fabricated PLA/MG based foams have the potential for specialized applications as an alternative to non-degradable petro-based foams in various fields of life.
Poly(lactic acid) (PLA) stands as a compelling alternative to conventional plastic-based packaging, signifying a notable shift toward sustainable material utilization. This comprehensive analysis illuminates the manifold applications of PLA composites within the realm of the food industry, emphasizing its pivotal role in food packaging and preservation. Noteworthy attributes of PLA composites with phenolic active compounds (phenolic acid and aldehyde, terpenes, carotenoid, and so on) include robust antimicrobial and antioxidant properties, significantly enhancing its capability to bolster adherence to stringent food safety standards. The incorporation of microbial and synthetic biopolymers, polysaccharides, oligosaccharides, oils, proteins and peptides to PLA in packaging solutions arises from its inherent non-toxicity and outstanding mechanical as well as thermal resilience. Functioning as a proficient film producer, PLA constructs an ideal preservation environment by merging optical and permeability traits. Esteemed as a pioneer in environmentally mindful packaging, PLA diminishes ecological footprints owing to its innate biodegradability. Primarily, the adoption of PLA extends the shelf life of products and encourages an eco-centric approach, marking a significant stride toward the food industry’s embrace of sustainable packaging methodologies.
Plastics have become an integral part of human life. Single-use plastics (SUPs) are disposable plastics designed to be used once then promptly discarded or recycled. This SUPs range from packaging and takeaway containers to disposable razors and hotel toiletries. Synthetic plastics, which are made of non-renewable petroleum and natural gas resources, require decades to perpetually disintegrate in nature thus contribute to plastic pollution worldwide, especially in marine environments. In response to these problems, bioplastics or bio-based and biodegradable polymers from renewable sources has been considered as an alternative. Understanding the mechanisms behind the degradation of conventional SUPs and biodegradability of their greener counterpart, bioplastics, is crucial for appropriate material selection in the future. This review aims to provide insights into the degradation or disintegration of conventional single-use plastics and the biodegradability of the different types of greener-counterparts, bioplastics, their mechanisms, and conditions. This review highlights on the biodegradation in the environments including composting systems. Here, the various types of alternative biodegradable polymers, such as bacterially biosynthesised bioplastics, natural fibre-reinforced plastics, starch-, cellulose-, lignin-, and soy-based polymers were explored. Review of past literature revealed that although bioplastics are relatively eco-friendly, their natural compositions and properties are inconsistent. Furthermore, the global plastic market for biodegradable plastics remains relatively small and require further research and commercialization efforts, especially considering the urgency of plastic and microplastic pollution as currently critical global issue. Biodegradable plastics have potential to replace conventional plastics as they show biodegradation ability under real environments, and thus intensive research on the various biodegradable plastics is needed to inform stakeholders and policy makers on the appropriate response to the gradually emerging biodegradable plastics.
A mesophilic bacterial strain, Bacillus safensis PLA1006, was isolated from landfill soil and was tested for growth on polylactic acid (PLA) emulsion medium. The strain formed clear zones on the medium and produced protease and lipase. The macroscopic morphology of the PLA films was not changed significantly after treatment with Bacillus safensis PLA1006 but the films were whitened. Weight loss of PLA films was about 8% after 30 days of incubation with Bacillus safensis PLA1006 in mineral salt medium. Scanning electron microscopy revealed etching on the surface of PLA film treated by Bacillus safensis PLA1006. This also caused an increase in hydrophilicity of the PLA films surface. Attenuated total reflectance - Fourier transform infrared spectroscopy analysis of PLA films after treated by Bacillus safensis PLA1006 showed no new absorption peaks but a decrease in the intensity of all absorption peaks. The hydrolysis products of PLA by the strain contained monomers and oligomers of lactic acid. Zymogram detection showed that proteases may play a role in the degradation of PLA.
The wide consumption of açaí fruit results in large amounts of seeds which end up in waste. These seeds have an advantageous composition for the development of biopolymers due to their fibers content and active components (responsible by functional properties as antioxidant capacity). In the present work, active polymers were generated incorporating açaí seed flour in sustainable films produced using starch from broken rice grains as matrix. The effects of different seed flour content (0%, 5%, 10%, and 15%) were studied on the physicochemical and structural properties of the polymers, and their antioxidant capacity. The packaging‐related properties were affected by the açaí seed flour incorporation mainly due to its high‐fiber content and polyphenolic compounds. The physicochemical and structural properties results demonstrated that the incorporation of 5% of açaí seed flour was the most appropriate, because of its better distribution in the film matrix. Free radical scavenging and reducing power assays indicated the antioxidant potential of the açaí seed flour incorporated films. Thus, active and sustainable polymers for food packaging can be obtained from açaí seeds and broken rice grains, generating new polymers and converting them into valuable raw materials in the market.
Jackfruit mucilage (JM) obtained from the fruit, Artocarpus heterophyllus was melt blended with poly(ε‐caprolactone) (PCL). The physical properties of the blends with more than 60 wt% PCL were investigated. Depression in the equilibrium melting temperature ( 𝑇𝑜𝑚) and the presence of extinction rings in the spherulites of PCL in the blends confirmed miscibility of the two components. The carbonyl and the COC groups of PCL and JM were responsible for the interactions as identified by Fourier transform infrared spectroscopy. The thermal stability of PCL decreased marginally in the blends with increasing JM content. The scanning electron microscopy (SEM) images indicated that no phase separation occurred. Porosity and the mechanical strength of the blends decreased with increasing JM content. Blends exposed to porcine pancreatic lipase showed enzymatic degradation of JM but not PCL and SEM images showed holes in the sample indicative of selective degradation of JM. Cell growth inhibition technique using the L929 fibroblasts cells showed the degree of inhibition was dependent on the increasing JM content in the blends. Blends with low JM content have the potential to be used for increased cell viability while blends with high JM content can be used for the treatment of cancer.
Chia seeds are a promising raw material for the development of biodegradable and edible polymers due to their composition and properties. This study aimed to evaluate the effects of drying process of chia mucilage (oven and freeze‐drying) and the incorporation of chia oil in films for food packaging. The films were formed by casting using chia mucilage and glycerol. The polymers developed were evaluated by physicochemical properties, microstructure, thermal properties, and biodegradation. The drying process of mucilage and oil incorporation in films affected mainly mechanical and color properties. Freeze‐dried mucilage resulted in superior mechanical performance. Differences were caused by the effect of drying process in the molecular structure of chia mucilage and the incorporation of oil among the polymer chains. Chia mucilage films were completely soluble in water and biodegraded in a short time in soil. These films are promising biodegradable polymers for the development of eco‐friendly food packaging and edible sachets for small pre‐measured portions, preventing environment pollution and facilitating product consumption.
A new bio-based hydrophobic gum arabic-based copolymer is an excellent adhesive and improves the properties of polylactic acid for potential food packaging applications. In recent years, bio-based polymers such as cellulose, chitosan, and gum arabic have attracted substantial interest because they are environmentally friendly, non-toxic, biodegradable, and have low carbon footprints. Currently, the potential applications for bio-based polymers are limited as they tend to be hydrophilic in their natural forms. However, if the polymers can be converted to hydrophobic materials, their potential applications increase dramatically. Here, we discuss our recent work on the modification of gum arabic (GA)-a natural polymer sourced from various acacia tree species-with oligo(L-lactic acid) (OLLA) using an in situ polycondensation reaction that does not require a catalyst or initiator, and produces a hydrophobic bio-based polymer suitable for adhesive and packaging applications.
Blends of poly(ε‐caprolactone) (PCL) with pine resin, an extract from the plant Pinus caribaea—Hondurensis was prepared by melt mixing in mass ratios from 90/10 to 50/50. The thermal, crystallization, morphological, and mechanical properties of the blends were studied by differential scanning calorimetry, Fourier transform infrared spectroscopy, polarized optical microscopy, scanning electron microscopy, and tensile test. Enzymatic degradation of the blends was investigated using porcine pancreatic and Candida rugosa lipase. Antimicrobial activity of the blends was tested against four strains of bacteria; Staphylococcus aureas, Escherichia coli, Bacillus subtilis, and Pseudomonas aeruginosa using the zone inhibition method. Miscibility of the blends was confirmed by the depression in the equilibrium melting temperature (Tm0) of PCL estimated from Hoffman–Weeks plot and the presence of extinction rings in the spherulites of blended PCL. Interactions between the two components involved the carbonyl and the C‐O‐C groups. The tensile strength of the blends with low pine resin content was comparable to PCL but decreased with higher pine gum content. Enzymatic degradation of the blends increased with increasing pine resin content. The blends showed antimicrobial property with all the bacteria except E. coli. The developed biomaterial shows promising candidacy in medical applications. POLYM. ENG. SCI., 1–10, 2018.
The current investigation addresses the thermal degradation and non-isothermal crystallization behaviour of the fabricated poly (lactic acid) foam (nPLA) and poly (lactic acid) (PLA)/cellulose nanocrystal (CNC) based foams at three different loadings of CNC (i.e. 1%, 2% and 3%) as PLA/CNC 1, PLA/CNC 2 and PLA/CNC 3 having highly porous, interconnected and microcellular morphology. The formation of various gaseous products at two different conversions (α = 0.3 and α = 0.7) are investigated by using thermogravimetric analyser hyphenated Fourier transmission infrared spectroscopy (TGA-FTIR) analysis in isothermal condition. Effect of porosity and CNC reinforcement towards thermal degradation and crystallization of the PLA is thoroughly investigated by using mercury intrusion porosimetry (MIP). "Model-free" and "modelistic" approaches like Friedman, Flynn-Wall-Ozawa (FWO), Kissinger-Akahira-Sinouse (KAS), Kissinger and Augis & Bennet have been utilized for non-isothermal degradation kinetics of the fabricated foams. Non-isothermal melt crystallization kinetics of fabricated foams reveals that both primary and secondary crystallization process taking place. The apparent activation energy calculated from FWO are ~175.8 kJ/mol, ~198.6 kJ/mol, ~175.5 kJ/mol and ~174.7 kJ/mol for nPLA, PLA/CNC 1, PLA/CNC 2 and PLA/CNC 3 respectively. It is also observed that at higher conversions, complex three dimensional diffusion mechanism of degradation might be taking place in accordance with Criado plots.
Thermal stability and thermal degradation kinetics of nanocomposites play an important role in many applications. In this study, nanocomposites based on poly (lactic acid) (PLA)/graphene containing 0.5 and 1 wt% were prepared via solution method. Functionalized graphene were prepared by acid treatment followed by grafting PLA on their surfaces. The functionalized graphene was characterized using fourier transform infrared spectroscopy (FTIR), Raman, elemental analysis, Fourier transform infrared attenuated total reflection (FTIR-ATR), Dynamic mechanical thermal analysis (DMTA) and thermogravimetry analysis (TGA). The results revealed a successful functionalization reaction. The morphology of nanocomposites was investigated by scanning electron microscopy (SEM). Thermal kinetics of samples was studied using TGA in multiple heating rates (5, 10, 20 and 30 °C/min). Flynn–Wall–Ozawa (FWO) and Vyazovkin (VYZ) methods were considered as isoconversional models. Although the assumptions of the applied models were different, there was a good agreement between the models and obtained activation energies.
The purpose of this research was to study the thermal degradation kinetics of nanocomposites of poly(l-lactide) (PLLA) with carbon nanotubes (CNT) in order to provide further insight into their thermal stability. Nanocomposites were prepared by solvent casting with 1, 3, and 5% by weight of pristine CNT (P-CNT) or functionalized CNT (F-CNT), and were characterized using infrared spectroscopy, transmission electron microscopy, differential scanning calorimetry, thermogravimetric analysis, and dynamic-mechanical-thermal analysis. The kinetic parameters of thermal decomposition were determined employing Coats-Redfern method to calculate the reaction order and E2 function model to calculate the activation energy (Ea). We found no major changes in PLLA glass transition temperatures due to CNT presence, but melt-crystallization temperature increased slightly in some composites. In general, composites consisting of 3% or 5% of F-CNT had superior thermal stability than did pure polymer or P-CNT composites. This improved thermal stability was revealed by slightly higher degradation and onset temperatures, and Ea obtained from kinetic analysis. In addition, 3% or 5% of F-CNT in PLLA composites slightly enhanced the storage modulus above the glass transition. Therefore, functionalization promoted, in some extent, better morphology and dispersion of CNT into the matrix, which was responsible for improved thermal stability and thermomechanical performance of composites at higher temperatures relative to pure polymer. POLYM. ENG. SCI., 2014. © 2014 Society of Plastics Engineers
Oligomers of lactic acid (LA) at different concentrations were melt-mixed with a polymeric matrix of high molecular weight polylactide (PLA) to improve their barrier properties. Purified and unpurified LA oligomers, obtained by a melt polycondensation reaction, were blended with PLA in order to study how the purification process affected the final film properties. In all the developed blend compositions, significant improvements in the permeability to both water and oxygen were observed in comparison with pure PLA, achieving permeability reductions of up to 54 %. This behaviour was ascribed to an antiplasticization phenomenon of the barrier properties related to the occupancy of the so-called Langmuir-free volume sites by the oligomer molecules. The results also showed that the permeability of these materials was greatly influenced by the presence of moisture, especially in the blends with unpurified oligomers. This behaviour was mainly ascribed to the higher content of the hydroxyl groups present in the latter materials, which led to an observable water sorption and hence to an increase in free volume for permeation.
Chemical and thermal characterization of poly(d,l-lactide-co-glycolide) (PLGA) composites filled with hydroxyapatite (HA) or carbon nanotubes (CNT) were evaluated by infrared spectroscopy, differential scanning calorimetry, thermogravimetry, and dynamic–mechanical–thermal analysis. The morphology and distribution of the nanoparticles were studied by transmission electron microscopy. The composites were prepared by solvent casting using 30% HA or 1, 3, and 5% of pristine and functionalized CNT as nanoparticles and PLGA 75:25 and PLGA 50:50 as copolymer matrix. The Coats–Redfern and E2 function methodologies were used to calculate the reaction order and the activation energy (Ea) of the thermal degradation process. It was found that the addition of nanoparticles increased the glass transition temperature (Tg) of the composites. Also, higher degradation temperatures and Ea values were obtained for PLGA–HA composites and compared with the neat copolymer, and the opposite behavior was exhibited by PLGA–CNT composites. The thermal and mechanical properties were highly dependent on the morphology and dispersion of the filler. The functionalization process of CNT promoted, to some extent, a better distribution and dispersion of CNT into the matrix, and these composites exhibited a slight enhancement on storage modulus. On the other hand, PLGA–HA composites showed a good dispersion but no improvement on the storage modulus below Tg. POLYM. ENG. SCI., 2013. © 2012 Society of Plastics Engineers
In this study, a novel 2-{[2-(3-thienyl)acetyl]oxy}ethyl2-methylacrylate (HEMAT) monomer was synthesized by esterification reaction of 2-hydroxyethyl methacrylate (HEMA) with 3-thiophene acetic acid. Homopolymer and random copolymer of HEMAT and methyl methacrylate (MMA) were prepared by bulk polymerization at 65 °C using AIBN as an initiator. The polymers were characterized by FT-IR and 1H NMR. PHEMAT and P(MMA-co-HEMAT) copolymer (95% PMMA–5% PHEMAT) were found to exhibit significantly enhanced properties compared to PMMA and PHEMA. Thermal behavior of HEMAT homopolymer and copolymer with MMA was also investigated by thermogravimetric analysis (TG). The apparent activation energies for thermal degradation of PHEMAT and P(MMA-co-HEMAT) were obtained by Kissinger and Tang methods. The results indicate that the side-chain thiophene units do have an influence on the effect follows the order P(MMA-co-HEMAT), PHEMAT, PHEMA and PMMA.
Homer Kissinger invented the peak displacement kinetic method that bears his name in the mid-1950s when he was an intern at the National Bureau of Standards. Because the method is rapid, easy-to-use, reliable, and uses readily available differential scanning calorimetry instrumentation, it is one of the most commonly used kinetic tools, having more than 2000 literature citations. The development of the method, Kissinger's scientific biography, advances to the approach, and practical experimental applications are reviewed.
A literature review is presented regarding the synthesis, and physicochemical, chemical, and mechanical properties of poly(lactic acid)(PLA). Poly(lactic acid) exists as a polymeric helix, with an orthorhombic unit cell. The tensile properties of PLA can vary widely, depending on whether or not it is annealed or oriented or what its degree of crystallinity is. Also discussed are the effects of processing on PLA. Crystallization and crystallization kinetics of PLA are also investigated. Solution and melt rheology of PLA is also discussed. Four different power-law equations and 14 different Mark–Houwink equations are presented for PLA. Nuclear magnetic resonance, UV–VIS, and FTIR spectroscopy of PLA are briefly discussed. Finally, research conducted on starch–PLA composites is introduced.
Sequential melt–solid polycondensation of lactic acid (LA) produces high molecular weight (MW) poly(lactic acid) (PLA), which is cost effective and can be put to a variety of uses, including packaging, biomedical and electrical appliances. This paper deals with the technology available for melt as well as solid state polycondensation of LA, the selection of catalysts, different synthetic methods, the effects of operating parameters on the MW of the product, and various properties of PLAs such as their physical, thermophysical, mechanical, electrical properties, degradation behavior and the dependence of these on the molecular weight. The kinetics and mechanisms involved in the different synthetic methods and degradation of the polymer are also discussed. Finally, a response optimization analysis used in the design of experiments (DOE), suggests a group of parameters under which one can achieve higher MW PLA, and provides mathematical relationships between synthesis parameters and the MW.
This article demonstrates the synthesis of lactic acid oligomer-grafted-chitosan (OLLA-g-CH), a nano-amphiphilic molecule, by in situ condensation polymerization and its effective use as a nano-filler for improvement in multiple properties of poly (lactic acid) (PLA) films, essential for stringent food packaging applications. Fourier Transform Infrared spectroscopy (FTIR) analysis shows the presence of amide-ester bond at 1539 cm-1 which confirms the structural grafting of OLLA chains with chitosan molecules. This nano-amphiphilic OLLA-g-CH molecule act as surfactant containing hydrophilic chitosan head and hydrophobic OLLA tails with average size in the range of ~2-4 nm. Prepared PLA/OLLA-g-CH bionanocomposite films appear with uniform dispersion of nano-amphiphilic OLLA-g-CH molecules with self-assembled micelles having size as low as ~20 nm and as high as ~150 nm with core-shell morphology in PLA matrix. This nano-filler is found very effective towards significant reduction in oxygen permeability (OP) by ~10 folds due to the reduction in solubility of oxygen molecules and improvement in crystal nucleation density due to availability of nano-nucleating sites. Ultimate tensile strength (UTS) of PLA/OLLA-g-CH bionanocomposite films are relatively comparable to that of PLA, however, elongation at break is improved significantly. The onset of thermal degradation of PLA/(OLLA-g-CH) films is also found comparable to that of PLA film. The glass transition temperature (Tg) of bionanocomposites is decreased by more than 18°C with increase in OLLA-g-CH loading which indicates the improved plasticization characteristics of PLA matrix. The crystallization kinetics suggest non-three dimensional truncated spherical structures, which is controlled by the combination of thermal and athermal instantaneous nucleations. POM analysis suggested that the spherulite growth of PLA is improved significantly with the addition of OLLA-g-CH. The reduction in Tg of PLA with improvement in elongation at break and multi-fold reduction in oxygen permeability offers this bionanocomposite films, a promising candidate for stringent food packaging applications.
The present work focuses on the microwave synthesis of lactic acid-grafted-gum arabic (LA-g-GA) by polycondensation reaction and its influence as an additive to improve the gas barrier properties of poly(lactic acid) (PLA) films, prepared by solution casting method. It is observed that during the synthesis of LA-g-GA, hydrophilic gum is converted into hydrophobic due to grafting of in situ grown hydrophobic oligo-(lactic acid). Subsequently, PLA/LA-g-GA bionanocomposite films are fabricated and characterized for structural, thermal, mechanical and gas barrier properties. Path breaking reduction in oxygen permeability (OP) of ∼10 folds is achieved in case of PLA films containing LA-g-GA as filler. However, water vapor transmission rate (WVTR) is reduced up to 27% after 5 wt % addition of filler. Reduction in OP of this order of magnitude enables the PLA to compete with PET in term of enhancing shelf life and maintaining the food quality. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016, 133, 43458.
Different kinds of biorenewable materials are rapidly emerging as potential alternatives to conventional petroleum-based synthetic materials. Among these materials, soy protein and its derivatives are of utmost interest and importance due to their advantages such as low cost, biodegradability, environmental friendliness, biocompatibility, renewability, and wide availability to name few. However, the poor physicochemical/mechanical properties as well as high moisture sensitivity of different soy based materials limit their successful applications in many fields. Different methodologies to produce new soy based materials with suitable functional groups are highly desired to increase their range of applications. So, in this Review, we have focused on the recent advances in the various graft copolymerization strategies involving soy and its applications. The synthesis, characterization, and methodology of graft-copolymer processing and resulting properties of the copolymers are fully covered. In this Review, we have attempted to provide a review of different soy protein based functional materials that will facilitate the development of a new generation of multifunctional biobased materials from biorenewable soy resources.
In the present study, biuret–formaldehyde (BF) polymeric ligand was prepared by condensation reaction, and its polymer metal complexes [BF-M(II)] were prepared with transition metal ions. Synthesized polymers were characterized by elemental, spectral, and thermal analyses. The geometry of central metal ions was determined using magnetic susceptibility measurement and electronic spectra, which reveals that Co(II) and Ni(II) ions have octahedral geometry, while Cu(II) and Zn(II) ions have square planer and tetrahedral geometry, respectively. Thermogravimetric (TG) analysis was used to estimate thermal and kinetic behavior of polymers at heating rates of 10, 15, and 20 °C min−1 under helium atmosphere. The TG curves of polymers at three heating rates were more or less in similar shape, which indicated that mass loss is independent of heating rate. Thermogravimetric data were analyzed by means of model-free isoconversional method of Flynn–Wall–Ozawa and Kissinger–Akahira–Sunose on the whole range of temperature. It was found that values of apparent activation energy (E
a) of [BF-M(II)] polymers are higher than BF and influenced by the metal type.
A physico-geometrical kinetic interpretation of the thermal degradation of poly(L-lactic acid) (PLLA) is described based on the results of a kinetic study using thermogravimetry (TG) and the microscopic observation of the reaction process. From the physico-geometrical viewpoint, the reaction process is separated into two different stages characterized by a surface reaction of the molten PLLA in the initial reaction stage followed by continuous bubble formation and disappearance in the established reaction stage. The generally reported trend of variation in the apparent activation energy as the reaction advances is explained by the partial overlapping of these two reaction stages. The kinetic rate data obtained using TG were kinetically separated into those for the respective reaction stages by optimizing the kinetic parameters. The significance of the kinetic results is discussed in terms of the physico-geometrical characteristics of the reaction. Such systematic kinetic analyses demonstrate the importance of considering the physico-geometrical perspective when interpreting the kinetic results for the thermal degradation of polymers.
A series of crosslinked hybrid poly(urethane–siloxane) networks based on comb-like structure co-poly(dimethyl)(methyl, hydroxypolyoxyethylenepropyl) siloxane cured with aliphatic diicocyanates hexamethylene diisocyanate (HDI), isophorone diisocyanate (IPDI), and 4,4′-methylenebis(cyclohexyl isocyanate) (H12MDI), were obtained. The samples have been submitted to thermal stability investigations at non-isothermal conditions in nitrogen and air. The thermal degradation behavior was investigated by evolved gas analysis, using coupled TG–FTIR technique. The kinetic parameters of the degradation process were determined both by isoconversional methods of Friedman and Ozawa–Flynn–Wall as well as by model fitting multivariate non-linear regression method. It was observed that the thermal stability of the poly(urethane–siloxane) thermosets depends on employed diisocyanate. The best fit of the f(α) function with the experimental data was found for two-step degradation mechanism. Successive stages of thermal decomposition occurred by diffusion and by the expanded Prout–Tompkins model, respectively.
The current work is focused on investigating the influence of novel bio-filler, "sucrose palmitate (SP)" on the thermal degradation behavior of poly(lactic acid) (PLA) biocomposites in order to render its suitability for food packaging application. Thermal degradation behavior of the PLA biocomposites was investigated by thermo-gravimetric analysis (TGA) using dynamic heating regime. The differential TG analysis revealed that there is no change in the Tmax value (357°C) for PLA and its composites up to 5 wt% of bio-filler loading. This reveals that the sucrose palmitate acts as a protective barrier by decelerating the thermal degradation rate of PLA. In the case of 10 wt% of the filler incorporated in the PLA matrix, Tmax rapidly shifted to lower temperature (324°C). This downturn in Tmax at higher loading of the filler is due to the increase in acidic sites and enhancement in the rate of degradation is observed. Differential scanning calorimetry (DSC) analysis revealed unimodal melting peak indicating the α-crystalline form of PLA. Based on the thermal degradation profile of sucrose palmitate, possible mechanism for degradation of PLA composites is proposed. The activation energies (Ea) of thermal degradation of PLA and PLA composites were evaluated by Flynn-Wall-Ozawa and Kissinger methods.
The thermal degradation of cellulose-graft-poly(l-lactic acid) at different heating rates in nitrogen was studied by thermogravimetric analysis (TGA) in the temperature range 20–550 °C. Nuclear magnetic resonance (NMR), wide-angle X-ray diffraction (WAXD), and differential scanning calorimetry (DSC) analyses were utilized to determine the microstructure and glass transition temperature of cellulose-graft-poly(l-lactic acid). The kinetic parameters were determined by using Friedman, Flynn–Wall–Ozawa, and Kissinger methods. Coats–Redfern method was used to investigate the probable degradation mechanism. The results indicated that the trend of activation energy of cellulose-graft-poly(l-lactic acid) increases with increasing the content of the poly(l-lactic acid) and the process of the non-spontaneous degradation stage, goes to a random nucleation with two nuclei on the individual particle mechanism, whose rate-controlling process could be described by conversion rate (α) (integral form 1/(1 − α)).
This paper presents a broad review on the recent advances in the research and development of biobased plastics and bionanocomposites that are used in various applications such as packaging, durable goods, electronics and biomedical uses. The development of biobased materials is driven by renewability, low carbon footprint and in certain cases biodegradability (compostability) issues and helped them in moving from niche markets to high-volume applications. The inherent drawbacks of some biobased plastics such as the narrow processing window, low heat deflection temperatures, hydrophilicity, poor barrier, and conductivity and inferior biocompatibility can be overcome by bionanocomposites. The first part of the paper reviews the recent advances in the development of biobased and biodegradable materials from renewable resources and their advantages and disadvantages. In the second part, various types of bionanocomposites based on four types of fillers i.e. nanocellulose, carbon nanotubes, nanoclays, and other functional nanofillers are discussed. This review also presents up-to-date progress in this area in terms of processing technologies, product development and applications.
The thermal degradation of polymers has been studied quite extensively using thermogravimetric measurements. For the kinetic description, most of the times single rate heating data and model-fitting methods have been used. Since the thermal degradation of the polymers is a very complex reaction, the choice of a reliable model or a combination of kinetic models is very important. The advantages or the disadvantages of using a single heating rate or multiple heating rates data for the determination of the kinetic triplet have been investigated. Also, the activation energy has been calculated with the isoconversional and model-fitting methods. The reaction model was determined with the model-fitting method. The limits of all these procedures were investigated with experimental data of the thermal degradation of the poly(ethylene adipate) (PEAd).
A novel phosphorus-containing poly(trimethylene terephthalate) (PTT) derived from 2-(6-oxido-6H-dibenz〈c,e〉〈1,2〉oxaphosphorin-6-yl)-1,4-hydroxyethoxy phenylene was synthesized via solid state polymerization, and its chemical structure was confirmed with 1H NMR. The thermal stability of the resulting copolyester was analyzed by thermogravimetric analysis. With the introduction of phosphorus-containing segments, polyester onset weight-loss temperatures in both nitrogen and air are enhanced. Thermal degradation kinetics were analyzed using the Flynn–Wall–Ozawa method, which showed a decreased activation energy for the copolyester compared with that for neat PTT, strongly suggesting that the increased onset weight-loss temperature in nitrogen is a result of enhanced carbonization. Microscale combustion calorimetry was carried out to test the flammability behavior of the copolyester; improved flame-retardant properties were observed with incorporated phosphorus components. Py-GC–MS testing revealed that the pyrolysis of phosphorus-containing copolyester is not significantly affected by the phosphorus incorporation.
The non-isothermal degradation kinetics of poly(trimethylene carbonate) (PTMC) and polyglycolide (PGL) was investigated by thermogravimetric (TG and DTG) analysis in the temperature range between 50 and 550 °C at different heating rates (0.5–40 °C/min). Both homopolymers showed a complex multi-step degradation process. Kinetic analysis was successfully performed for the main degradation steps using the isoconversional Kissinger–Akahira–Sunose and Friedman methods. Activation energies of these steps were practically independent of the degree of conversion. The true kinetic triplets (E, A, f(α)) were determined by the Coats–Redfern method. The results clearly indicated that the two homopolymers mainly degraded by quite different mechanisms, i.e. A3 and F1, which may be associated with different depolymerization processes (e.g. decarboxylation or unzipping).Degradation of copolymers of trimethylene carbonate and glycolide with different chemical microstructures (i.e. random, blocky and segmented) and of blends with different percentages of both homopolymers was also studied. Interestingly, a deceleration and an acceleration for the decomposition of trimethylene carbonate and glycolide segments were observed, respectively. Specifically, the two-step degradation process of the blend with 50 wt% of each homopolymer was analyzed by the above methodologies. Kinetic data indicated that the main degradation process involved a different mechanism from that previously determined for PTMC and PGL, and that the activation energy was intermediate (i.e. EPTMC < EBlend < EPGL).
Polypropylene-random copolymers are a relatively new type of polypropylene (PP) modified plastics, which were introduced over the last years on the market. The comonomer which is most commonly used is ethylene at random concentrations for the improvement of mechanical and thermal properties of the final material. For the present work, we characterized and compared the mechanical properties and the thermal degradation kinetics results of polypropylene-random copolymer (PP-R) with 7% ethylene content and polypropylene-random copolymer/enhanced crystalline structure/improved temperature resistance (PP-RCT), which is formed by using a special β-nucleation process, which leads to a homogenous dispersion of equal sized β-crystals. The tensile strength properties of PP-RCT are improved due to the presence of both α- and β-crystals, making the final product more ductile than neat PP or its random copolymer (PP-R), which both consist exclusively of α-crystals (monoclinic system). Characterization with XRD and DSC confirmed the two crystalline phases of PP-RCT. Thermogravimetric (TG) studies of PP-RCT showed that the new material exhibits better thermal stability than neat PP-R, since 1% mass loss of PP-RCT appeared at temperatures 10 °C higher than neat PP-R. The activation energy of degradation of PP-RCT and PP-R was calculated using the Kissinger, Akahira and Sunose (KAS) method. Degradation took place into two stages; the first stage which corresponded to an initial small mass loss was simulated with an n-th order model (Fn), while the second stage was attributed to the main degradation mechanism of the material and was simulated with an n-th order model with autocatalysis (Cn). When the calculated activation energies with isoconversional and model-fitting methods are compared, PP-RCT has much higher activation energy than PP-R, a fact which indicates the higher thermal stability of PP-RCT.
The degradation during the melt processing of poly(lactic acid) (PLA) and its nanocomposites with different contents (0.5 and 2.5%) of an organomodified montmorillonite (OMMT) promoted physical and chemical changes in their properties. Extrusion and injection of PLA/OMMT nanocomposites have been responsible for a decrease in molecular weight. Exfoliation/intercalation phenomena and loss of crystallinity have been detected by means of X-ray diffraction. The thermal stability of the materials has been assessed by thermogravimetric analysis (TG). An integral method based on the general analytical solution as well as differential and special methods have been used to study the kinetics of the thermal decomposition. It has been demonstrated that activation energy had a significant dependence on conversion. The trend of variation has been found to be different for nanocomposites compared to that for the polymer matrix, thus confirming a different competition between the main reaction mechanisms (cis-elimination and intramolecular transesterification).
The nature and the extent of degradation of poly(hydroxy ether of bisphenol-A) phenoxy resin were analysed by thermogravimetry (TGA/DTGA) under nitrogen and air atmosphere. Decomposition kinetics were elucidated according to Flynn–Wall–Ozawa, Friedman and Kissinger methods. The evolved gases during degradation were inspected by a thermogravimetry analyser coupled with Fourier Transform Infrared Spectrometer (TGA/FTIR) and also with a TGA coupled to a Mass Spectrometer (TGA/MS). Mass spectra showed that chemical species evolved in phenoxy decomposition in air were very similar to those assigned from degradation in nitrogen (water, methane, CO, CO2, phenol, acetone, etc.). However, these species appear in different amount and at different temperatures in both atmospheres. FTIR analysis of the evolved products showed that water and methane were the beginning decomposition products, indicating that decomposition is initiated by dehydration and cleavage of C–CH3 bond in the bisphenol-A unit of phenoxy resin. After this initial stage, random chain scission is the main degradation pathway. Nevertheless, in air atmosphere, previously the complete decomposition of the phenoxy obtaining fundamentally CO2, and water, the formation of an insulated surface layer of crosslinked structures has been proposed.
Gum from Acacia senegal has been fractionated using hydrophobic affinity chromatography. Characterization, including identification of sugars and determination of protein and amino acid contents, has been undertaken for each fraction together with measurements of molecular mass and molecular mass distribution using laser light scattering and gel permeation chromatography. The results have indicated that the gum consists of three distinct components. Fraction 1, which represents 88.4% of the total, is an arabinogalactan with molecular mass 2.79 × 105 and is deficient in protein. Fraction 2, which represents 10.4% of the total, is an arabinogalactan—protein complex with a molecular mass of 1.45 × 106, containing ~50% of the total protein. It is envisaged that on average each molecule of fraction 2 consists of five carbohydrate blocks of molecular mass ~2.8 × 105 covalently linked through a chain of amino acid residues. Fraction 3 represents only 1.24% of the total gum but contains ~25% of the total protein and has been shown to consist of one or more glycoproteins. Whereas the proteinaceous components of fractions 1 and 2 contain predominantly hydroxyproline and serine, this is not the case for fraction 3.
Proteolysis of Acacia senegal gum by pronase leads to subunits of ~200 000 weight-average mol. wt. The origin of gum heterogeneity is discussed and considered to be due to a variable number of sub-units linked to a protein core.
The isoconversional method for the determination of energies of activation from the reciprocal temperature at which a fraction of conversion was reached in experiments at differing constant heating rates is reviewed and amplified. The error introduced into the calculation of activation energy by the use of a linear approximation of the logarithm of the temperature integral is discussed. Methods for the correction of this error are developed and a table of correction factors are given.
In the framework of environmentally-friendly processes and products, polylactide (PLA) represents the best polymeric substitutes for various petropolymers because of its renewability, biodegradability, biocompatibility and good thermomechanical properties. Initially, most of its applications concerned biomedical sector and short-time uses such as packaging, particularly for the biodegradable properties of PLA. Interestingly, due to the depletion of petroleum resources, PLA is now viewing more and more as a valuable biosourced polymer alternative in long-term applications such as automotive, electronics, etc. However, for such applications, PLA suffers from some shortcomings such as low thermal resistance, heat distortion temperature and rate of crystallization, whereas some other specific properties are required by different end-use sectors (flame retardancy, antistatic to conductive electrical characteristics, anti–UV, antibacterial or barrier properties, etc.). Therefore, adding nanofillers represents an interesting way to extend and to improve the properties of PLA. There are many nanofillers (three-dimensional spherical and polyhedral, two-dimensional nanofibers or one-dimensional sheet-like nanoparticles) that have been studied, with satisfactory achievements, in the design of PLA nanocomposites. This review hence highlights the main researches and developments in PLA-based nanocomposites during this last decade.
(Available online 20 June 2013)
A new method of obtaining the kinetic parameters from thermogravimetric curves has been proposed. The method is simple and applicable to reactions which can not be analyzed by other methods. The effect of the heating rate on thermogravimetric curves has been elucidated, and the master curve of the experimental curves at different heating rates has been derived.
The applications of the method to the pyrolyses of calcium oxalate and nylon 6 have been shown ; the results are in good agreement with the reported values.
The applicability of the method to other types of thermal analyses has been discussed, and the method of the conversion of the data to other conditions of temperature change has been suggested. From these discussions, the definition of the thermal stability of materials has been criticized.
A novel biodegradable poly(ester urethane; PEU) was synthesized by chain extension reaction of dihydroxylated poly(L-lactic acid; PLLA) and poly(butylene succinate; PBS) using diisocyanate as a chain extender. The kinetics of thermal and thermo-oxidative degradation of PEU containing PLLA and PBS blocks were studied by thermogravimetric analysis (TGA). TGA results indicated that PEU was more stable in air than in nitrogen and went through a two-stage degradation process irrespective of the experimental atmosphere. Activation energy of each stage was calculated by means of Kissinger, Kim-Park, Friedman, Flynn-Wall-Ozawa, and Kissinger-Akahira-Sunose methods. For the first stage, the activation energy value obtained in air was slightly higher than the corresponding value obtained in nitrogen; and for the second stage, the activation energy showed a much higher value in air than in nitrogen. The Coats-Redfern method was employed to study the degradation mechanism of each stage. The results indicated that the degradation of the first stage follows the P3/4 mechanism irrespective of the experimental atmosphere; the degradation of the second stage of PEU obeys the P1 mechanism in nitrogen while P3/2 in air.
The effects of the kinetics of reactions of the type solid → solid + gas on the corresponding differential thermal analysis pattern are explored. Curves of reaction rate vs. temperature for constant heating rates constructed by analytical methods are used to demonstrate the effect of varying order of reaction. The information so obtained is used to analyze the differential thermal patterns of magnesite, calcite, brucite, kaolinite, and halloysite. The results of the differential thermal study agree with results obtained isothermally except in some specific cases.
This work investigates the development, optimization and in vitro characterization of calcium alginate/gum Arabic beads by an ionotropic gelation method for prolonged sustained release of glibenclamide. The effects of amount of sodium alginate and gum Arabic as independent process variables on the drug encapsulation efficiency and drug release were optimized and analyzed based on central composite design and response surface methodology. Increment in drug encapsulation efficiency and decrease in drug release were found with the increase of both the amounts of sodium alginate and gum Arabic, used as polymer-blend. These optimized beads showed high drug encapsulation efficiency (86.02±2.97%), and suitable sustained drug release pattern over prolonged period (cumulative drug release after 7h of 35.68±1.38%). The average size of these formulated dried beads containing glibenclamide ranged from 1.15±0.11 to 1.55±0.19mm. The in vitro dissolution of these beads showed prolonged sustained release of glibenclamide over 7h, which followed first-order model (R(2)=0.9886-0.9985) with anomalous (non-Fickian) diffusion mechanism (release exponent, n=0.72-0.81). The swelling and degradation of the optimized beads were influenced by pH of test mediums. These beads were also characterized by SEM and FTIR spectroscopy for surface morphology and excipients-drug interaction analysis, respectively. These developed calcium alginate/gum Arabic beads containing glibenclamide could possibly be advantageous in terms of advanced patient compliance with reduced dosing interval.
An amorphous grade Poly (lactic acid) (PLA) was selected for an accelerated burial in soil test during 450 days. Thermogravimetric analyses were carried out to study the effects of degradation in soil on the thermal stability and the thermal decomposition kinetics. A single stage decomposition process is observed for all degradation times. It is shown that the thermal stability of PLA is slightly affected by degradation in soil. Concerning the study of the thermal decomposition kinetics, Criado master curves were plotted from experimental data to focus the study of the thermodegradation kinetic model.The kinetic methods proposed by Broido and Chang were used to calculate the apparent activation energies (Ea) of the degradation mechanism. These results were compared to the Ea values obtained by the method developed by Coats and Redfern in order to prove the applicability of the former methods to the kinetic study. As expected, non-linear tendency is found out for Ea variation along the degradation times, which can be explained as an evolution by stages.
Poly(l-lactide) (i.e. poly(l-lactic acid) (PLLA)) and poly(d-lactide) (i.e. poly(d-lactic acid) (PDLA)) and their equimolar enantiomeric blend (PLLA/PDLA) films were prepared and the effects of enantiomeric polymer blending on the thermal stability and degradation of the films were investigated isothermally and non-isothermally under nitrogen gas using thermogravimetry (TG). The enantiomeric polymer blending was found to successfully enhance the thermal stability of the PLLA/PDLA film compared with those of the pure PLLA and PDLA films. The activation energies for thermal degradation (ΔEtd) were evaluated at different weight loss values from TG data using the procedure recommended by MacCallum et al. The ΔEtd values of the PLLA/PDLA, PLLA, and PDLA films were in the range of 205–297, 77–132, and 155–242 kJ mol−1 when they were evaluated at weight loss values of 25–90% and the ΔEtd value of the PLLA/PDLA film was higher by 82–110 kJ mol−1 than the averaged ΔEtd value of the PLLA and PDLA films. The mechanism for the enhanced thermal stability of the PLLA/PDLA film is discussed.
Poly(3-hydroxybutyrate) (PHB)/organically modified clay nanocomposites were prepared by the melt mixing method and were characterized using wide-angle X-ray diffraction. Their thermal degradation kinetics was investigated using thermogravimetric analysis at various heating rates. Further kinetic analysis was performed using isoconversional methods and the invariant kinetic parameters method was used to estimate the so-called ‘true’ kinetic parameters, i.e. the pre-exponential factor, A and the activation energy, E, as well as the reaction model. It was found that intercalated structures are formed and the thermal stability of the material is improved by the addition of the nano-filler. From the isoconversional analysis, it was found that the activation energy does not vary significantly with the degree of degradation denoting degradation in one step with similar values for pure PHB and for all nanocomposites. Using the invariant kinetic parameters method, it was found that the model that best describes the experimental data was that of Sestak–Berggren's with f(a) = αn(1 − α)m, where the value of n is always larger than m and is increasing with the amount of the nano-filler. The value of the ‘true’ activation energy was found to be about 100 kJ mol−1 for all nanocomposites and the pre-exponential factor for PHB was estimated equal to 5.35 × 109 min−1. Finally, the values of the kinetic rate constant k were found to decrease with the amount of the nano-filler up to 3 wt%, while for amounts larger than 3 wt% k increased reaching a value greater than that of pure PHB for the 10 wt% nanocomposites.
Thermal decomposition of poly(lactic acid) (PLA) has been studied using thermogravimetry coupled to Fourier transform infrared
spectroscopy (TGA-FTIR). FTIR analysis of the evolved decomposition products shows the release of lactide molecule, acetaldehyde,
carbon monoxide and carbon dioxide. Acetaldehyde and carbon dioxide exist until the end of the experiments, whereas carbon
monoxide gradually decreases above the peak temperature in that the higher temperature benefits from chain homolysis and the
production of carbon dioxide. A kinetic study of thermal degradation of PLA in nitrogen has been studied by means of thermogravimetry.
It is found that the thermal degradation kinetics of PLA can be interpreted in terms of multi-step degradation mechanisms.
The activation energies obtained by Ozawa–Flynn–Wall method and Friedman’s method are in good agreement with that obtained
by Kissinger’s method. The activation energies of PLA calculated by the three methods are 177.5kJmol−1, 183.6kJmol−1 and 181.1kJmol−1, respectively.
There have been substantial developments recently concerning the regulatory aspects of gum arable and the elucidation of its structure and functional characteristics. The aim of this paper is to present the position with regard to its current legal definition, to summarize what is now known about the structure of this complex polysaccharide and to illustrate how the structural features relate to its functional properties, notably its ability to stabilize oil-in-water emulsions and to form concentrated solutions of low viscosity.
The thermal decomposition of the biologically degradable polymer poly(lactic acid) (PLA) was investigated by means of several thermoanalytical techniques: thermogravimetry, differential scanning calorimetry, time resolved pyrolysis-MS and pyrolysis-GC/MS. The results mainly confirm reaction mechanisms proposed in the literature. The dominant reaction pathway is an intramolecular transesterification for pure PLA (Tmax = 360 °C), giving rise to the formation of cyclic oligomers. In addition, acrylic acid from cis-elimination as well as carbon oxides and acetaldehyde from fragmentation reactions were detected. PLA samples contaminated with residual Sn from the polymerization process show a preceding selective depolymerization step (Tmax = 300 °C) which produces lactide exclusively. The GC analysis of the oligomers gives insight into the stereochemistry of the original polymer chain with respect to the configuration of the asymmetric C atoms, as well as into the stereochemistry of decomposition reactions. Other experimental findings, which do not fit the proposed reaction mechanisms, are also discussed.
A boron-containing layered hydroxy salt (LHS), ZHTMDBB, was prepared and compounded with a highly flammable synthetic polymer, poly (methyl methacrylate) {PMMA}, via melt blending: the composite structure was intercalated with poor dispersion. The effect of this LHS on the flammability, thermal stability and degradation kinetics of PMMA was investigated via cone calorimetry and thermogravimetric analysis. The addition of 3–10% by mass of ZHTMDBB to PMMA resulted in significant reduction of peak heat release rate (22–48%) of the polymer and improvements in thermal stability were observed in both air and nitrogen. Effective activation energies for the degradation process were evaluated using Flynn-Wall-Ozawa, Friedman, and Kissinger methods. All three methods indicated that the additive increased the activation energies of the first step of the degradation process in both air and nitrogen. Activation energies of the second step were lowered in nitrogen but were not significantly affected in air.
Semi-interpenetrating network (SISH-GA) composed of gum arabic and crosslinked copolymer of poly(2-hydroxyethyl methacrylate-co-acrylic acid) was synthesized in the presence of initiator ammonium persulfate (APS), crosslinker N,N'-methylene bis acrylamide (MBA), catalyzed by [CuSO4/glycine] chelate complex and finally loaded nanoparticle inside the networks via in situ reduction of silver nitrate (AgNO3) using trisodium citrate (Na3C6H5O7) as reducing agent. Characterization of the product was performed along with its degradability in Escherichia coli medium.
This paper presents a review of the industrially most relevant exudate gums: gum arabic, gum karya, and gum tragacanth. Exudate gums are obtained as the natural exudates of different tree species and exhibit unique properties in a wide variety of applications. This review covers the chemical structure, occurrence and production of the different gums. It also deals with the size and relative importance of the various players on the world market. Furthermore, it gives an overview of the main application fields of the different gums, both food and non-food.
A novel magnetic nano-adsorbent was developed by treating Fe(3)O(4) nanoparticles with gum arabic to remove copper ions from aqueous solutions. Gum arabic was attached to Fe(3)O(4) via the interaction between the carboxylic groups of gum arabic and the surface hydroxyl groups of Fe(3)O(4). The surface modification did not result in the phase change of Fe(3)O(4), while led to the formation of secondary particles with diameter in the range of 13-67nm and the shift of isoelectric point from 6.78 to 3.6. The amount of gum arabic in the final product was about 5.1wt%. Both the naked magnetic nanoparticles (MNP) and gum arabic modified magnetic nanoparticles (GA-MNP) could be used for the adsorption of copper ions via the complexation with the surface hydroxyl groups of Fe(3)O(4) and the complexation with the amine groups of gum arabic, respectively. The adsorption rate was so fast that the equilibrium was achieved within 2min due to the absence of internal diffusion resistance and the adsorption capacities for both MNP and GA-MNP increased with increasing the solution pH. However, the latter was significantly higher than the former. Also, both the adsorption data obeyed the Langmuir isotherm equation. The maximum adsorption capacities were 17.6 and 38.5mg/g for MNP and GA-MNP, respectively, and the Langmuir adsorption constants were 0.013 and 0.012L/mg for MNP and GA-MNP, respectively. Furthermore, both the adsorption processes were endothermic due to the dehydration of hydrated metal ions. The enthalpy changes were 11.5 and 9.1kJ/mol for MNP and GA-MNP, respectively. In addition, the copper ions could desorb from GA-MNP by using acid solution and the GA-MNP exhibited good reusability.
- Carrasco
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