Green Composites of Poly (Lactic Acid) and Sugarcane Bagasse Residues from Bio-refinery Processes

Twin-screw extrusion was used to prepare the composites consisting of PLA and three types of sugarcane bagasse residues (up to 30 wt%) derived from different steps of a biorefinery process. Each residue had different composition, particle size and surface reactivity due to chemical and biological (enzyme, microbes) treatments that the biomass was subjected to. The effects of different residue characteristics on properties, crystallization behaviors and morphologies of PLA composites were investigated. Besides, a small amount (2 wt%) of coupling agent, Desmodur^® VKS 20 (DVKS), was used to improve the interfacial bonding between PLA and bagasse residues. The results indicated that in the presence of 2 % DVKS, PLA composite with pretreated residue exhibited the maximum strength properties (98.94 % tensile strength and 93.91 % flexural strength of neat PLA), while PLA composite with fermentation residue exhibited the minimum strength properties (88.98 % tensile strength and 81.91 % flexural strength of neat PLA).     

High Toughness and Fast Crystallization Poly(Lactic Acid)/Polyamide 11/SiO<Subscript>2</Subscript> Composites

A poly(lactic acid) (PLA)/polyamide 11 (PA11)/SiO₂ composite was mixed from PLA, PA11, and nanosilica particles through twin-screw extrusion. The PLA/PA11/SiO₂ composite was evaluated with tensile and Izod impact tests, light transmission and haze measurement, and isothermal and nonisothermal crystallization behavior determinations. The PLA/PA11/SiO₂ (97.0/3.0) composite had approximately 10.8% less ultimate tensile strength than neat PLA, but it had greater ductility and approximately ninefold greater elongation at break. A dimple morphology was observed on the fractural surface of the PLA/PA11/SiO₂ composite, indicating that the incorporation of PA11 and nanosilica particles increased the ductility of the PLA matrix. PLA with less than 3 wt% of PA11 and 0.5 phr of nanosilica particles had an Izod impact strength of 8.72 kJ/m². PA11 and nanosilica particles effectively toughened this PLA polymer; they accelerated both isothermal and nonisothermal crystallization rates and increased the crystallinities of the resulting composites under isothermal and nonisothermal crystallization processes.     

Characterization and Properties of Reactive Poly (Lactic Acid)/Ethylene–Vinyl Alcohol Copolymer Blends with Chain-Extender

A hydrophilic copolymer, ethylene–vinyl alcohol (EVOH), was incorporated into the poly(lactic acid) (PLA) matrix to improve the barrier property of PLA through twin-screw extrusion rather than the typical coextrusion process. A chain extender, poly[(ethylene)-co-(methyl acrylate)-co-(glycidyl methacrylate)] (PEMG), was used to reduce the probability of the thermal degradation of PLA during melt compounding. Biaxial stretching was used to enhance the microstructure and barrier property of PLA-PEMG/EVOH films. Experimentally, PEMG considerably reduced the probability of the thermal degradation of the PLA-PEMG sample. Biaxial stretching increased the tensile strength and decreased the value of elongation at break of the PLA-PEMG/EVOH80 (PLA/EVOH 100/80) film. Because of the efficient blending of PLA/EVOH in the twin-screw extruder, the dispersion of EVOH in the PLA matrix revealed homogeneous dispersion with a domain size of 1–5 μm. EVOH effectively improved the water vapour transmission rate (WVTR) of PLA through melt blending. Blending PLA-PEMG with EVOH substantially decreased the WVTR from 250 cc—20 μm/m²-day-atm for neat PLA to approximately 65 cc—20 μm/m²-day-atm for the PLA-PEMG/EVOH80 film, a decrease of approximately 74 % compared with neat PLA. Moreover, the WVTR decreased further from 65 cc—20 μm/m²-day-atm for the unstretched PLA-PEMG/EVOH80 film to 6.3 cc—20 μm/m²-day-atm for the film stretched at a stretch ratio of 3.5 × 3.5 and at 100 %/s, a decrease of approximately 90 % compared with neat PLA.     

Stiff Biodegradable Polylactide Composites with Ultrafine Cellulose Filler

Polylactide (PLA) composites with 10–30 wt% of commercial fine grain filler of native cellulose were prepared by melt-mixing, and examined. The composite films had esthetic appearance, glossy surface, creamy color and density close to that of neat PLA. Good dispersion of the filler in PLA matrix was achieved. The composites were stiffer than neat PLA; in the glassy region the storage modulus increased by approx. 30 %. The tensile strength of the composite materials in the temperature range from 25 to 45 °C was similar to that of neat PLA. No marked decrease in molar mass of PLA in the composites occurred during processing in comparison to neat PLA. Moreover, thermogravimetry experiments demonstrated good thermal stability of the composites; 5 % weight loss occurred well above 300 °C.     

Effect of Hydrothermal Aging on Injection Molded Short Jute Fiber Reinforced Poly(Lactic Acid) (PLA) Composites

This work focused on the durability of short jute fiber reinforced poly(lactic acid) (PLA) composites in distilled water at different temperatures (23, 37.8 and 60 °C). Morphological, thermal and mechanical properties (tensile, flexural, and impact) of jute/PLA composites were investigated before and after aging. Different from traditional synthetic fiber reinforced polymer composites, the stability of jute/PLA composites in water was significantly influenced by hydrothermal temperature. The mechanical properties of the composites and molecular weight of PLA matrix declined quickly at 60 °C, however, this process was quite slower at temperatures of 23 and 37.8 °C. Impact properties of the composites were hardly decreased, but the tensile and flexural properties suffered a drop though to various degrees with three degradation stages at 23 and 37.8 °C. The poor interface of composites and the degradation of PLA matrix were the main damage mechanism induced by hydrothermal aging. Furthermore, considering the hydrolysis of PLA matrix, the cleavage of PLA molecular chain in different aging time was quantitatively investigated for the first time to illustrate hydrolysis degree of PLA matrix at different aging time.     

Study on the Effect of Dicumyl Peroxide on Structure and Properties of Poly(Lactic Acid)/Natural Rubber Blend

In attempt to enhance the compatibility of NR in PLA matrix, and furthermore to enhance mechanical properties of PLA, PLA/NR blends with strong interaction were prepared in Haake internal mixer, using dicumyl peroxide (DCP) as cross-linker. The effects of dicumyl peroxide on morphology, thermal properties, mechanical properties and rheological properties of PLA and PLA/NR blends were studied. The results indicated that dicumyl peroxide could increase the compatibility of poly(lactic acid) and natural rubber. With small amount of dicumyl peroxide, the effect on NR toughening PLA was enhanced and the tensile toughness of PLA/NR blends was improved. When the DCP content was up to 0.2 wt%, the PLA/NR blend reached the maximum elongation at break (26.21 %) which was 2.5 times of that of neat PLA (the elongation at break of neat PLA was 10.7 %). Meanwhile, with introducing 2 wt% DCP into PLA/NR blend, the maximum Charpy impact strength (7.36 kJ/m²) could be achieved which was 1.8 times of that of neat PLA (4.18 kJ/m²). Moreover, adding adequate amount of DCP could improve the processing properties of blends: the viscosity of PLA/NR blend decreased significantly and the lowest viscosity of the blends could be achieved when the DCP content was 0.5 wt%.     

Comparative Investigations on Optimum Polymerization Conditions for the Synthesis of a Sustainable Poly(Lactic Acid)

The development of synthetic biodegradable polymers using solvent free polymerization has a unique potential to be used as sustainable polymers in biomedical applications. The aim of this work was to synthesize and characterize a sustainable class of poly(lactic acid) (PLA) under different operating conditions via direct polycondensation of lactic acid (LA). Several parameters were tested including the absence of solvents and catalysts on the polymerization, in addition to polymerization temperature and time. Polymerization conditions were evaluated using response surface method (RSM) to optimize the impact of temperature, time, and catalyst. Results showed that molecular weight (M_w) of PLA increased with increasing polymerization time. Highest M_w of 28.4 kD with relatively a broad polydispersity 1.9 was achieved at polymerization temperature 170?°C at 24 h in the free solvent polymerization. This led to a relevant inherent viscosity of 0.37 dl/g. FTIR spectra exhibited a disappearance of the characteristic peak of the hydroxyl group in LA at 3482 cm^?1 by increasing the intensity of carbonyl group. The ¹H nuclear magnetic resonance (NMR) exhibited the main chain at 5.22 ppm and the signal of methyl proton at 1.61 ppm as well as a signal at 4.33 and 1.5 assigned to the methane proton next to the terminal hydroxyl group and carboxyl group respectively. Meanwhile, the PLA synthesized with a catalyst [Sn(Oct)₂] in a free solvent demonstrated comparatively high thermal transition properties of glass transition, melting, and crystallinity temperatures of 48, 106, and 158?°C, respectively. These results are of significant interest to further expand the use of PLA in biomedical applications.     

Production of Poly(l-Lactide)-Degrading Enzyme by Amycolatopsis orientalis ssp. orientalis and Its Catalytic Ability in Biological Recycling of Poly(l-Lactide)

The fermentation conditions for poly(l-lactide) (PLA)-degrading enzyme production by Amycolatopsis orientalis ssp. orientalis were statistically optimized by response surface methodology. The optimal value of the most important factors was 0.39 % PLA and 0.34 % gelatin for 2.81 days of cultivation. Under these conditions, the model predicted a PLA-degrading activity of 155.30 U/l. The verification showed the production amount of 154.2 U/l. The crude enzyme from A. orientalis ssp. orientalis showed potent PLA-degrading ability, which is efficient for the biological recycling of PLA. Up to 4,000 mg/l of PLA granule was completely degraded within 5 days at 45 °C by the crude enzyme. l-lactic acid (600 mg/l) was obtained as a degradation product of PLA after only 2 h of incubation. The results indicated that the crude PLA-degrading enzyme from A. orientalis ssp. orientalis has the potential to degrade PLA to lactic acid for the recycling of PLA industry and waste disposal.     

Mechanical Properties of Poly (Lactic Acid)/Hemp Fiber Composites Prepared with a Novel Method

This research dealt with a novel method of fabricating green composites with biodegradable poly (lactic acid) (PLA) and natural hemp fiber. The new preparation method was that hemp fibers were firstly blending-spun with a small amount of PLA fibers to form compound fiber pellets, and then the traditional twin-screw extruding and injection-molding method were applied for preparing the composites containing 10–40 wt% hemp fibers with PLA pellets and compound fiber pellets. This method was very effective to control the feeding and dispersing of fibers uniformly in the matrix thus much powerful for improving the mechanical properties. The tensile strength and modulus were improved by 39 and 92 %, respectively without a significant decrease in elongation at break, and the corresponding flexural strength and modulus of composites were also improved by 62 and 90 %, respectively, when the hemp fiber content was 40 wt%. The impact strength of composite with 20 wt% hemp fiber was improved nearly 68 % compared with the neat PLA. The application of the silane coupling agent promoted further the mechanical properties of composites attributed to the improvement of interaction between fiber and resin matrix.     

Effects of Alkali Treatment on the Properties of Short Flax Fiber–Poly(Lactic Acid) Eco-Composites

In this study, the influence of alkali (NaOH) treatment on the mechanical, thermal and morphological properties of eco-composites of short flax fiber/poly(lactic acid) (PLA) was investigated. SEM analysis conducted on alkali treated flax fibers showed that the packed structure of the fibrils was deformed by the removal non-cellulosic materials. The fibrils were separated from each other and the surface roughness of the alkali treated flax fibers was improved. The mechanical tests indicated that the modulus of the untreated fiber/PLA composites was higher than that of PLA; on the other hand the modulus of alkali treated flax fiber/PLA was lower than PLA. Thermal properties of the PLA in the treated flax fiber composites were also affected. T_g values of treated flax fiber composites were lowered by nearly 10 °C for 10% NaOH treatment and 15 °C for 30% NaOH treatment. A bimodal melting behavior was observed for treated fiber composites different than both of neat PLA and untreated fiber composites. Furthermore, wide angle X-ray diffraction analysis showed that the crystalline structure of cellulose of flax fibers changed from cellulose-I structure to cellulose-II.     

Effect of Fiber Surface Treatments on Thermo-Mechanical Behavior of Poly(Lactic Acid)/Phormium Tenax Composites

In the present study, Phormium Tenax fiber reinforced PLA composites were processed by injection molding and twin screw compounding with a fiber content ranging from 10 to 30 wt%. Three surface treatment methods have been used to improve the Phormium Tenax fiber-matrix interfacial bonding that are as follows: (1) aqueous alkaline solution, (2) silane coupling agent, and (3) a combination of alkaline and silane treatment. The mechanical, thermal and morphological properties of the resulting composites were investigated. The results have shown that the moduli of surface treated fiber reinforced composites are lower than the ones obtained for untreated composites (as a consequence of the decrease in fiber modulus caused by the chemical treatments) and no significant increase in strength was observed for any of the composites compared to neat PLA. SEM micrographs of composite fractured surfaces confirmed an improvement in the interfacial strength, which was insufficient nonetheless to significantly enhance the mechanical behavior of the resulting composites. Results from thermogravimetric analysis and differential scanning calorimetry suggest that surface treatment of Phormium affects the ability of PLA to cold crystallize, and the thermal stability of the composites at the different fiber contents was reduced with introduction of alkali and silane treated Phormium fibers.     

Mechanical Properties and Isothermal Crystallization Behaviour of Poly(lactide)/Poly(methyl methacrylate)/α-Cellulose Composites

Polylactide (PLA)/polymethylmethacrylate (PMMA)/α-cellulose composites were fabricated using a twin-screw extruder. During fabrication, α-cellulose short fibres were incorporated for improving the toughness of the brittle PLA and a chain extender was used for reducing PLA hydrolysis. Highly transparent PLA and PMMA were blended to obtain miscible and transparent blends. For evaluating the performance of the PLA/PMMA/α-cellulose composites, a series of measurements, including tensile and Izod impact tests, light transmission and haze measurements, thermomechanical analysis, and determination of isothermal crystallisation behaviour, was conducted. Adding the chain extender considerably reduced the occurrence of hydrolytic degradation. Both the chain extender and α-cellulose short fibres increased the elongation at break and Izod impact strength of the composites. Compared with the neat PLA, including 1.0 wt% α-cellulose short fibres increased the elongation at break and Izod impact strength of the composite PLA by approximately 211 and 219 %, respectively. According to the observed mechanical performance, the optimal blending ratios for PLA and PMMA were between 90:10 and 80:20. The total light transmittance of the composites was as high as 91 %, indicating that the PLA/PMMA blend was highly miscible. The haze value of the PLA/PMMA/α-cellulose composites was lower than 32 %. Incorporating cellulose short fibres increased the number of crystallisation sites and crystallinity of the PLA/PMMA/α-cellulose composites while reducing the spherulite dimensions.     

Preliminary environmental impact assessment of PFOS waste treatment in a lab-scale batch subcritical water decomposition operation

Life cycle assessment (LCA) was carried out by SimaPro 7.3 to study the environmental impact of a lab-scale batch subcritical water decomposition operation for a kilogram of Perfluorooctane sulfonic acid (PFOS) waste treatment in this study, a proven process for the decomposition of PFOS pollutants with high concentration. This LCA focuses on not only the main environmental factors from emissions of toxic pollutants, but also the influence from technical characteristics of the iron-induced subcritical water technology including energy and substances consumption during the subcritical water decomposition treatment process. The IMPACT 2002+ environmental model was used to evaluate the 15 midpoint and 4 end-point environmental damages. It was found that the energy consumption to sustain the high temperature (350 °C) and high pressure (23 MPa) in the subcritical water process contributes 99.8 % of the damages. The total negative impact of the SCWD process for 1 kg of PFOS waste treatment to human health, ecological quality, climate change and resources amounts to 1.11 × 10^?3, 8.43 × 10^?5, 9.76 × 10^?4, 9.05 × 10^?4 Pt, respectively. And the improvement of energy efficiency and catalytic effectiveness are two important factors to reduce the environmental impact from the SCWD process for the treatment of PFOS waste.     

Environmental Impact Assessment of Polylactide(PLA)/Chicken Feathers Biocomposite Materials

The aim of this study is to analyse the environmental impacts (EIs) of the process of preparation of new biocomposite materials obtained from polylactide (PLA) and chicken feathers (CFs). Two CFs stabilization methods and different percentages of CFs have been studied. The EIs of these new composites were compared to the impact of virgin PLA. Cradle-to-gate life cycle inventories were assessed for 0–35% v/v of CFs in a CFs/PLA biocomposite. Two CFs stabilization processes, autoclave and surfactant, were tested and compared with the aim to prioritize one of them from the environmental point of view. A composite plate of 184?×?184?×?2.2 mm³ was defined as the functional unit. Autoclave stabilization process exhibited lower environmental impact compared with surfactant stabilization process mainly due to both the lower requirements of electricity and water and the reduced pollution loads of the generated wastewater. Thus, the autoclave process was selected as the standard method when comparing the EIs of the proposed CFs/PLA biocomposites. In this sense, the addition of CFs to PLA matrix proportionally reduces all the EIs compared to pure PLA due to the replacement of PLA with CFs. This behaviour can be explained because the PLA production accounts for the 99% of the impact of the biocomposite. Consequently, CFs conveniently stabilized might be an alternative raw material to prepare CFs/PLA biocomposites with less environmental impact compared to pure PLA.     

Grafting of Glycidyl Methacrylate onto Poly(lactide) and Properties of PLA/Starch Blends Compatibilized by the Grafted Copolymer

Poly(lactide)-graft-glycidyl methacrylate (PLA-g-GMA) copolymer was prepared by grafting GMA onto PLA in a batch mixer using benzoyl peroxide as an initiator. The graft content was determined with the ¹H-NMR spectroscopy by calculating the relative area of the characteristic peaks of PLA and GMA. The result shows that the graft content increases from 1.8 to 11.0 wt% as the GMA concentration in the feed varies from 5 to 20 wt%. The PLA/starch blends were prepared by the PLA-g-GMA copolymer as a compatibilizer, and the structure and properties of PLA/starch blends with or without the PLA-g-GMA copolymer were characterized by SEM, DSC, tensile test and medium resistance test. The result shows that the PLA/starch blends without the PLA-g-GMA copolymer show a poor interfacial adhesion and the starch granules are clearly observed, nevertheless the starch granules are better dispersed and covered by PLA when the PLA-g-GMA copolymer as a compatibilizer. The mechanical properties of the PLA/starch blends with the PLA-g-GMA copolymer are obviously improved, such as tensile strength at break increasing from 18.6 ± 3.8 MPa to 29.3 ± 5.8 MPa, tensile modulus from 510 ± 62 MPa to 901 ± 62 MPa and elongation at break from 1.8 ± 0.4 % to 3.4 ± 0.6 %, respectively, for without the PLA-g-GMA copolymer. In addition, the medium resistance of PLA/starch blends with the PLA-g-GMA copolymer was much better than PLA/starch blends.     

Water transport in polylactic acid (PLA), PLA/ polycaprolactone copolymers, and PLA/polyethylene glycol blends

Polylactic acid (PLA) is a hydrolytically degradable aliphatic polyester, and water vapor permeability may have a significant influence on the rate of degradation. A method is devised to use bags prepared from PLA films and filled with molecular sieves to determine the water vapor permeability in the polymer, its copolymers with caprolactone, and blends with polyethylene glycol. The “solution-diffusion” model is used to determine the permeability parameters. These include the solubility coefficient,S, a measure of the equilibrium water concentration available for hydrolysis and the diffusion coefficient,D, which characterizes the rate of water vapor diffusion into the film under specific conditions. Values ofS andD at 50‡C and 90% relative humidity ranged from 400 × 10^-6 to 1000 × 10^-6 cm³ (STP)/(cm³ Pa) and 0.20 × 10^-6 to 1.0 × 10^-6 cm²/s, respectively. TheS andD coefficients were also measured at 20 and 40‡C and compared to those of other polymers. The degree of crystallinity was found to have little influence on the measured permeability parameters. The heat of sorption, δH_S, and the activation energy of diffusion, E_D, were used to show that the permeability process is best described by the “water cluster” model for hydrophobic polymers. Finally, the diffusion coefficient is used to compare the rate of water diffusion to the rate of water consumption by ester hydrolysis. Results indicate that hydrolytic degradation of PLA is reaction-controlled.     

Water Absorption Kinetics and Hygrothermal Aging of Poly(lactic acid) Containing Halloysite Nanoclay and Maleated Rubber

Poly(lactic acid)/halloysite nanoclay composites (PLA/HNC) containing maleic anhydride grafted styrene-ethylene/butylene-styrene (SEBS-g-MAH) were produced using melt compounding followed by compression molding. The effects of hygrothermal aging on the thermal properties and functional groups changes of the HNC reinforced PLA (with and without SEBS-g-MAH) at three different temperatures (i.e., 30, 40 and 50 °C) were analyzed using differential scanning calorimetry and Fourier transform infrared spectroscopy techniques. The diffusion coefficient (D) of PLA was decreased by the incorporation of HNC and SEBS-g-MAH. The activation energy of water diffusion (E _a ) of PLA/HNC/SEBS-g-MAH nanocomposites was higher than that of pure PLA. The glass transition temperature (T _g ), cold-crystallization temperature (T _cc ) and melting temperature (T _m ) of the PLA sample were shifted to lower temperature and the effect was more pronounced at 50 °C. The carbonyl index values of all PLA samples increased after immersed in 40 and 50 °C, which is due to the formation of higher amount of carboxyl groups during the hydrolysis process.     

Influence of Hygrothermal Ageing on the Physico-Mechanical Properties of Alkali Treated Industrial Hemp Fibre Reinforced Polylactic Acid Composites

30 wt% aligned untreated long hemp fibre/polylactic acid (AUL) and aligned alkali treated long hemp fibre/polylactic acid (AAL) composites were produced by film stacking and subjected to hygrothermal ageing environment along with neat polylactic acid (PLA). Hygrothermal ageing was carried out by immersing samples in distilled water at 25 and 50 °C over a period of 3 months. It was found that both neat PLA and composites followed Fickian diffusion. Higher temperature generally increased the Diffusion coefficient, D of neat PLA and composites, as well as shortening the saturation time. Neat PLA had the lowest D value followed by AAL composites and then AUL composites. After hygrothermal ageing, tensile and flexural strength, Young’s and flexural modulus and K _Ic were found to decrease and impact strength was found to increase for both AUL and AAL composites. AUL composites had greater overall reduction in mechanical properties than that for AAL composites after hygrothermal ageing. Crystallinity contents of the hygrothermal aged composites support the results of the deterioration of mechanical properties upon exposure to hygrothermal ageing environment.     

Biodegradability of Epoxidized Soybean Oil Based Thermosets in Compost Soil Environment

In this study, bio-thermoset from epoxidized soybean oil (ESO) was prepared in the presence of methylhexahydrophthalic anhydride curing agent and 2-ethyl-4-methylimidazole catalyst. The crosslink densities of the synthesized ESO are ranged from 0.109 × 10^?3 to 0.308 × 10^?3 mol/cm³. The ESO bio-thermosets were exposed to the soil-burial test for 8 months. Weight change and morphology of the degraded ESO specimens were assessed. It was found that the weight loss of ESO was governed by the materials compositions, crosslink density and the soil-burial exposure time. The 3 mm thickness ESO bio-thermosets with crosslink density of 0.109 × 10^?3 mol/cm³ had fully biodegraded after soil-burial for 6 months. In addition, 16S rDNA sequencing was carried out to identify the soil microorganisms. It was suggested that Comamonas sp., Bacillus sp., Streptomyces sp. and Acinetobacter sp. are the possible soil microbes that degrade the ESO bio-thermosets in the compost soil environment.     

Poly(Ethylene Glycol) Grafted Starch Introducing a Novel Interphase in Poly(Lactic Acid)/Poly(Ethylene Glycol)/Starch Ternary Composites

The main purpose of this study is challenging to dramatically improve the toughness of poly(lactic acid) (PLA)/starch by adding poly (ethylene glycol) (PEG) into the composites and grafting PEG molecules onto the surface of starch particles. It was found that the surface grafting of PEG onto starch induced the presence of PEG-rich regions located around the starch particles, caused by migration and aggregation of free PEG molecules. A novel interphase transition layer between PLA and starch was formed, which showed great ability for cavitation and vested large-scaled plastic deformation to PLA matrix. Further mechanical properties tests indicated the formation of interphase layer significantly increase the elongation at break from 10.2 to 254.5%, and notched impact strength from 1.56 to 2.37?kJ/m² for PLA/PEG/starch ternary composites. The influence of PEG component, ethanol extraction and annealing was also investigated.