PLA Biocomposites Research Articles

Biodegradation and characterization study of compostable PLA bioplastic containing algae biomass as potential degradation accelerator

This study demonstrated the degradation behavior of poly(l-lactic acid) (PLA)/algae biomass biocomposites under abiotic (58 ± 2 °C) and at thermophilic composting conditions (58 ± 2 °C). In the biodegradation study, laboratory synthesized, custom-made poly(ε-caprolactone) (PCL) pellets and its dumbbells were considered as the second bioplastic component in order to develop a comparative data of PLA based biocomposites. In experimental work 1, PLA based biocomposites highlighted that chain scission alone could not produce enough oligomers for microbial assimilation and provided information related to critical molecular weight, which marked the sudden weight loss of materials. In experimental work 2, laboratory synthesized PCL and its biocomposites were used along with PLA based samples for the biodegradation study. This was done to spawn a more precise comparative notion on the biodegradation process of PLA based samples following ASTM International D5338–15. Addition of 5-wt% of deoiled algae biomass in PLA showed an incremental effect on biodegradation of PLA biocomposites. High elemental nitrogen content in the algae biomass accelerated the degradation process in the PLA biocomposites by fueling up the microbial growth. This study will help in designing PLA based biocomposites using algae biomass as well as other nitrogen rich fillers, which might increase the biodegradability of PLA based polymers under different environment.

Preparation of Chemically Modified Lignin-Reinforced PLA Biocomposites and Their 3D Printing Performance.

Using a simple esterification reaction of a hydroxyl group with an anhydride group, pristine lignin was successfully converted to a new lignin (COOH-lignin) modified with a terminal carboxyl group. This chemical modification of pristine lignin was confirmed by the appearance of new absorption bands in the FT-IR spectrum. Then, the pristine lignin and COOH-lignin were successfully incorporated into a poly(lactic acid) (PLA) matrix by a typical melt-mixing process. When applied to the COOH-lignin, interfacial adhesion performance between the lignin filler and PLA matrix was better and stronger than pristine lignin. Based on these results for the COOH-lignin/PLA biocomposites, the cost of printing PLA 3D filaments can be reduced without changing their thermal and mechanical properties. Furthermore, the potential of lignin as a component in PLA biocomposites adequate for 3D printing was demonstrated.

Effect of freeze‐dried durian skin nanofiber on the physical properties of poly(lactic acid) biocomposites

AbstractDurian skin wastes generated by durian fruit or Durio zibethinus Murray shows potential as a new natural fiber‐based reinforcement for polymers. Freeze drying (FD) method is reported able to reduce the size of particles. Thus, in this research, durian skin nanofiber (DSNF) is developed using a FD process from durian skin fiber (DSF) and its effect on poly(lactic acid) (PLA) biocomposite is investigated. Cinnamon essential oil was added as a plasticizer for PLA biocomposite. Morphological analysis via transmission electron microscopy and scanning electron microscopy showed that FD method reduced the DSF particle size into DSNF. Dynamic light scattering was also performed to see the size distribution of DSNF particle after the freeze dried process. The hydrophobicity of the biocomposite was measured by contact angle and UV transmittance was done to analyze its transparency and UV penetration. The tensile strength of these composites showed significant changes in the presence of DSF and DSNF in PLA.

Microfibrillated cellulose from sweet sorghum (Shorghum Bicolor (L.) Moench) fiber by twin screw extruder and its charateristics on polylactic acid biocomposites

High tensile strength and modulus could be obtained by microfibrillated cellulose (MFC) addition into PLA matric. MFC production from sweet sorghum fiber with twin screw extruder (TSE) could be an effective mechanical treatment. The objective of this research is to study the effectivity of twin screw extruders for MFC production from sweet sorghum fiber and to analyze its effect on PLA biocomposites properties. Sorghum fiber was firstly delignificated with alkaline treatments and bleached with sodium peroxide solution to produce high cellulose content of fiber. Bleached sorghum fiber was then passed through into TSE for 1, 3, and 5 passes. Afterward, PLA biocomposites with MFC from TSE process were produced by the solvent casting method. Twin screw extruder with co-rotating intermeshing flow is effective for defibrillation and size reduction of cellulose fibers which could achieve 1-10 μm in diameter and millimeters in length.. The tensile strength of PLAM_TSE5 increase 4.54% in 50.60 Mpa and modulus of elasticity increase 40.36% in 2.82 Gpa. Storage modulus of PLAM_TSE5 also increases 10.64% in 3.088 Mpa compare to pure PLA.

Effect of chemical and enzymatic treatments of alfa fibers on polylactic acid bio-composites properties

Poor interfacial adhesion between vegetable fibers and bio-based thermoplastics is recognized as a serious drawback for biocomposite materials. To be applicable for a large-scale production, one should consider appropriate methods of natural fiber handling. This study presented poly(lactic acid) (PLA) reinforced with Alfa short fibers and four types of fiber treatment were selected. The effect of these treatments on the tensile properties and the morphology of biocomposites was studied. Composite samples were produced using a twin-screw extruder and an injection molding machine with a fiber percentage of 20 wt %. Prior to composite manufacture, Alfa fibers were subjected to mechanical, chemical and enzymatic modifications. The comparison of enzyme treated fibers and NaOH treated fibers was investigated by means of biochemical and morphological analyses. It was observed that enzymes decompose lignin, pectin and hemicelluloses from the fiber bundles interface leading to the reduction of technical fiber diameter and length. The elimination of these hydrophilic components resulted also in an increase of the water resistance of treated fibers. A bigger fiber-matrix interface area was thus created, which facilitated fiber-matrix adhesion and enhanced mechanical characteristics of the composites. SEM micrographs showed homogeneous distribution of treated fibers in the polymer matrix. Tensile strength of PLA biocomposites filled with pectinase treated fibers was increased by 27% over untreated samples. The data proved that enzymatic treatment can be used as an effective and ecofriendly strategy of fiber modification for natural fiber-reinforced composite production. These materials can be used in several domains such as construction, automotive applications and packaging industries.

Influence of amorphous cellulose on mechanical, thermal, and hydrolytic degradation of poly(lactic acid) biocomposites

Eco-friendly materials such as poly(lactic acid) (PLA) and cellulose are gaining considerable interest as suitable substitutes for petroleum-based plastics. Therefore, amorphous cellulose (AC) was fabricated as a new reinforcing material for PLA biocomposites by modifying a microcrystalline cellulose (MCC) structure via milling. In this study, the mechanical properties, thermal properties, and degradability of PLA were analysed to compare the effects of both MCC and AC on PLA. The tensile and impact properties improved at an optimum value with AC at 8 wt% and 4 wt% fibre loading, respectively. Notably, a scanning electron micrograph analysis revealed improved AC fibre–matrix adhesion, compared with MCC fibre–matrix adhesion, as well as excellent interaction between AC and PLA. Both MCC and AC improved the hydrolytic degradation of PLA. Moreover, the biocomposites with AC exhibited superior degradation when the incorporation of AC improved the water absorption efficiency of PLA. These findings can expand AC applications and improve sustainability.

Pyrolysis kinetics and mechanical properties of poly(lactic acid)/bamboo particle biocomposites: Effect of particle size distribution

Abstract Bamboo particle (BP)-reinforced poly(lactic acid) (PLA) biocomposites were fabricated. The effect of the BP particle size distribution on the pyrolysis and mechanical properties of PLA biocomposites was evaluated. The optimum particle size of BP for improving the tensile strength PLA biocomposites is 200 mesh (16.6–84.5 µm). The pyrolysis mechanism and kinetics were studied according to the Coats–Redfern method. The addition of BP inhibited the pyrolysis process of PLA. The activation energy of biocomposites ranged from 120.7 to 151.5 kJ/mol, which is significantly higher than that of the neat PLA. The pyrolysis mechanisms of biocomposites are attributed to the chemical reaction at low pyrolysis temperature (270–400℃) and ash layer diffusion control at high pyrolysis temperature (400–600℃). Crystallization behavior of biocomposites showed that small BPs in PLA biocomposites generated more cross-linking points in the PLA matrix, which constrained the movement of the molecular chain and acted as an effective nucleating agent in promoting the crystallization process. The pyrolysis behavior and mechanical properties analysis provide critical information for potential large-scale production of the PLA biocomposites.

Monitoring of mechanical performances of flax non-woven biocomposites during a home compost degradation

Non-woven composites reinforced with plant fibers are widely used in the automotive and construction sectors. The vast majority is composed of petroleum-based, non-compostable polyolefins, which are no longer a viable solution in an environmental context where the end-of-life management of industrial products is becoming a major societal issue. Here, fully green composites are produced by reinforcing three bio-based and biodegradable matrices – poly-(hydroxyalkanoate) (PHA), poly-(butylene-succinate) (PBS) and poly-(lactide) (PLA) – with non-woven flax fiber preforms. Notably, their mechanical performance was observed to be at least equivalent to the industry reference – poly-(propylene) (PP) reinforced non-woven flax. These composites were then buried in an instrumented garden compost, and the evolution in microstructure and mechanical properties was studied over a period of six months. Microtomography studies revealed that evolution in composite microstructure principally depended on the polymer matrix: surface degradation was predominant for PBS and PHA biocomposites, whereas rapid fiber-matrix interface degradation in the core was observed for PLA biocomposites. Interestingly, even after six months in the compost, all composites exhibit tensile strengths of at least 50% of their initial value. Moreover, the strength reduction in biodegradable composites was of the same magnitude as the industry reference, flax/PP composite. These results demonstrate the potential of biocomposites in resolving the ‘biodegradation paradox’: flax composites with biopolymers like PLA, PHA and PBS can be designed to have adequate mechanical performance for industrial products, even after ageing in harsh conditions, and yet offer an alternative end-of-life route to the typical incineration (with or without energy recovery).

Improved Mechanical Properties and Flame Retardancy of Wood/PLA All‐Degradable Biocomposites with Novel Lignin‐Based Flame Retardant and TGIC

AbstractIn this study, a type of all‐degradable flame retardant wood/poly(lactic acid) (PLA) biocomposite (FPW) with low cost and excellent mechanical properties is prepared and studied. A novel lignin‐based phosphorus‐containing flame retardant (LMD) is synthesized first. PLA, wood powder, poly(butyleneadipate‐co‐terephthalate), triglycidyl isocyanurate (TGIC), and LMD are then melt‐blended to prepare FPW. The limiting oxygen index value of PLAF25L15‐4T (25% of L15MD and 4% of TGIC) reaches 28.6%. Furthermore, the residue at 700 °C is up to 31.3%, which apparently helps to increase the flame retardancy of FPW. Its tensile strength is as high as 48.7 MPa. The interfacial compatibilization is much improved as proved by scanning electron microscopy observation. This should be due to the in situ interfacial reaction between PLA, wood, and TGIC, and the lignin component both in wood and LMD. The obtained PLA biocomposite with improved mechanical and flame retardant properties is promising for its wide applications.

Erratum: Influence of pulp bleaching and compatibilizer selection on performance of pulp fiber reinforced PLA biocomposites

Erratum: Influence of pulp bleaching and compatibilizer selection on performance of pulp fiber reinforced PLA biocomposites

Effect of carbon-rich biochar on mechanical properties of PLA-biochar composites

Agricultural biomass residues are emerged from harvesting and processing of agricultural crops. When the crop production increases, a large amount of biomass residues is produced and remained after cutting of peel, bunch, straw and stalk of crops. In this work, agricultural biomass residues (cassava rhizome, durian peel, pineapple peel and corncob) were selected as feedstock for carbon-rich biochar (CRB) production using a facile pyrolysis method. Proximate analysis and thermogravimetric analysis (TGA) were used to characterize biomass feedstock. The results showed that the percentage of fixed carbon in biomass feedstock ranged between 11.91% and 17.51%. Characteristic differences of the CRB were investigated using scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDS), Fourier transform infrared spectroscopy (FTIR) and Raman spectroscopy. The carbon content in the CRB was found to significantly depend on biomass origin. Interestingly, cassava rhizome, which has a higher percentage of fixed carbon, is a superior precursor for CRB production. The study of different pyrolysis temperature indicated that the carbon content of cassava rhizome derived CRB is increased with pyrolysis temperature. The tensile properties of composite between poly(lactic acid) PLA and different types of biomass-derived CRB were investigated. PLA composite incorporated with a higher carbon content-CRB tended to exhibit improved mechanical properties. Specifically, the elastic modulus and impact energy of PLA/CRB composite specimens increased remarkably with the incorporation of CRB powder. The current research indicates that CRB prepared from agricultural biomass residues could be a sustainable material for utilization in PLA biocomposites.

Influence of pulp bleaching and compatibilizer selection on performance of pulp fiber reinforced PLA biocomposites

ABSTRACTThis article focuses on the effect of pulp bleaching and emerging commercial compatibilizers on physical performance of pulp fiber reinforced poly(lactic acid) (PLA) biocomposites. Industrially bleached and unbleached hardwood kraft pulp fibers are treated with several additive types, and compounded with PLA to fiber content of 30 wt %. After injection molding, the produced biocomposites are evaluated by their mechanical performance and fiber–matrix adhesion. For selected materials, fiber surface and fiber properties are reflected to composite performance by analyzing the compositions, dimensions, and lignin coverage of original fibers, as well as fiber dispersion and dimensions after melt processing. As a conclusion, unbleached kraft pulp fibers provide significant improvement in physical properties of PLA/pulp fiber composites. Of the screened compatibilizers, epoxidated linseed oil has a clear positive effect on performance when bleached kraft pulp fibers are used. The improvements correspond to enhanced fiber–matrix adhesion and differences in remaining fiber length distributions. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019, 136, 47955.

Flame retardant poly (lactic acid) biocomposites based on azo‐boron coupled 4,4′‐sulfonyldiphenol and its combination with calcium lignosulfonate—Crystalline and mechanical properties

Poly (lactic acid) (PLA) has become an important biopolymer with excellent properties but has limited engineering applications where fire safety is ultimate. An efficient flame retardant (FR) for PLA biocomposites based on azo‐boron coupled with 4,4′‐sulfonyldiphenol‐(((1E,1′E)‐(sulfonylbis(6‐hydroxy‐3,1‐phenylene))bis (diazene‐2,1‐diyl))bis(3,1‐phenylene))diboronic acid (SBDA) was synthesized and characterized by FTIR, 1H and 13C NMR spectra. SBDA was combined with calcium lignosulfonate (Calig) and compounded with PLA, and the FR, crystallization, and mechanical properties were investigated. The addition of 15 wt% FR (10 wt% Calig and 5 wt% SBDA) into PLA led to important reductions in peak heat release rate (PHRR) approximately 54%, total heat release (THR) approximately 28.6%, and the average effective heat of combustion (AEHC) approximately 29.4%. The fire performance index and fire growth index improved by approximately 56.4% and 33.1%, respectively. A V‐0 rating (vertical burning test) and a limiting oxygen index value of 28.8% were achieved for the FR PLA biocomposites. The combinatory SBDA/Calig reduced the segmental mobility of PLA in the organic‐inorganic interface with insignificant changes in the elongation at break and the Young Modulus. TG‐IR study showed significant reductions in pyrolysis gaseous products for the composites compared with PLA. This research work will expand the frontiers of knowledge on use of boron and calcium functionalized polyaromatic polyols for reducing the flammability of PLA.

The influence of treated eucalyptus microfibers on the properties of PLA biocomposites

Eucalyptus sawdust was used for nano and microfibers preparation by a “green” process (ball milling), followed by surface treatments (alkaline and surfactant) and incorporated in PLA, from 1 to 10 wt %, aiming for the preparation of films of biocomposites. The treatments applied exposed the polar groups due to lignin removal or by the surfactant adsorption, respectively. The modification intensified the interaction in the interface region between the fibers and the PLA matrix (SEM), maintaining thermal properties (DSC results). The fibers treatments contributed to the films hydrophobicity concerning the humid environments, as evidenced by the results of moisture absorption and contact angle. However, the decrease in the crystallinity index of the biocomposites (4.2%, obtained by DSC) contributed to the increase of the water molecules diffusion (D, water absorption) caused by the structure disorder, which may favor the post-use biodegradation process. The mechanical properties of the films were promising, presenting values always above the PLA property. In general, the results suggest that the incorporation of eucalyptus fibers, mainly detergent treated, improves not only the mechanical properties of PLA but also favors properties that enhance the biodegradation process of the post-use biocomposites.

Thermal and biodegradation properties of poly(lactic acid)/rice straw composites: effects of modified pulping products

In this work, rice straw (RS) as an abundant biomass was chemically thermoplasticized through alkali pulping and benzylation reactions, which destroy inter- and intra-molecular hydrogen bonding of the lignocellulosic constituents and dissociate the cellulosic component of RS from lignin. Two different products of RS benzylation process including benzylated pulp (BP) and pulping liquor (BL) rich in cellulose, with the former, and lignin, with the latter, were incorporated into poly(lactic acid) (PLA) using a twin-screw extruder. By substituting the hydroxyl groups of the lignocellulosic constituents with non-polar benzyl groups, the filler/PLA interfacial adhesion was improved considerably in which no evidence of debonding was observed on cryofractured surfaces of the PLA/BL composites. Indoor soil biodegradation test was performed on samples for 128 days and their weight loss, water uptake, visual observations and crystallization were investigated. While PLA sheets showed negligible deterioration and roughly kept their whole weight, the PLA biocomposites demonstrated considerable degradation after soil burial test due to the higher water absorption, lower glass transition temperature and larger biodegradation rate of fillers. The modified pulping products of RS showed a higher thermal stability than their thermoset-like predecessors. The non-isothermal DSC results demonstrated that the addition of BP and BL particles to PLA reduced the glass transition and melting temperatures of the matrix and resulted in higher degree of crystallinity. The findings showed that RS pulping and benzylation reactions successfully led to more effective fillers for PLA than rice straw.

Effect of hydrolyzed collagen on thermal, mechanical and biological properties of poly(lactic acid) bionanocomposites

Bionanocomposites based on poly(lactic acid) (PLA), plasticized with commercial tributyl o-acetyl citrate (ATBC) and containing hydrolyzed collagen (HC) up to 10 wt% and silver nanoparticles (AgNPs), were prepared by a melt mixing procedure. The properties of antimicrobial PLA based formulations were investigated in terms of morphology (atomic force microscopy, AFM), mechanical, thermal (differential scanning calorimetry, DSC), spectral (by attenuated total reflectance, Fourier-transform infrared spectroscopy), cell proliferation (by flow cytometry) and immunohistochemical properties induced by collagen. The incorporation of HC into antimicrobial PLA biocomposites led to the slight reduction both in mechanical properties and the degree of crystallinity with respect to those of PLA/ATBC sample. These properties can be attributed to the smooth surface improvement of the bionanocomposite. In vitro testing using L929 fibroblasts in the presence of PLA-based bionanocomposites showed that all samples presented good biocompatibility, as it was indicated by the cell cycle distribution and DNA content analyses. Furthermore, these new biocomposites induced an increase of collagen production in vitro. Overall, PLA/HC5/AgNPs and PLA/HC10/AgNPs bionanocomposites showed very good in vitro biocompatibility, and therefore, could be considered as valuable materials for medical devices, such as tubes, catheters, drains or connectors, with a relatively long service life.

Poly(l-lactic acid) bio-composites reinforced by oligo(d-lactic acid) grafted chitosan for simultaneously improved ductility, strength and modulus.

PLA bio-composites reinforced by oligo(d-lactic acid) grafted chitosan has been developed for simultaneously improved ductility, strength and modulus. Brittleness problem greatly limits the applications of PLA, a polymer derived from corn. Various methods have been developed to solve the brittleness problem. Unfortunately, these methods have their limitations, such as sacrifice of strength and modulus of PLA, use of toxic chemicals and high costs. Bio-based elastomers such as chitosan also have poor compatibility with PLA, leading to poor mechanical properties. The hypothesis for this research is that CS-g-oligo(D-LA) particles with good ductility could form strong interfacial interactions with PLLA matrix. Reinforcing effect of CS-g-oligo(D-LA) particles on PLLA matrix was systematically studied. Compatibility and intermolecular interactions between CS-g-oligo(D-LA) particles and PLLA matrix were studied by SEM, DSC and 13C NMR analyses. The reinforcing mechanism was summarized. Due to effective transfer of stress from PLLA matrix to the strong but ductile skeletons of CS-g-oligo(D-LA), ductility, strength and modulus of PLLA bio-composites were substantially improved. This novel reinforcing strategy via formation of strong interactions between enantiomeric lactyl units would enrich the fabrication and exploration of high-performance PLA-based bio-composites.

Comparative study of the extrinsic properties of poly(lactic acid)-based biocomposites filled with talc versus sustainable biocarbon.

This study investigates the effects talc and two sizes of biocarbon have as fillers in a PLA bioplastic, when considering them for durable composite applications. Analysis of the PLA-based biocomposites' resistance to wear and flammability accompanied by the vapor barrier characteristics were conducted, with subsequent rheological and thermal properties to further explain the observed results. The compression molded sheets showed a reduction in abrasion by greater than 69% for either filler type compared to the neat PLA due to their high stiffness. In contrast, only the talc provided barrier properties that hindered both water and oxygen permeability, while biocarbon did not possess a high aspect ratio to form a tortuous path necessary for barrier improvement. Yet, the biocarbon-filled PLA biocomposites provided superior flammability resistance due to its char-like caricature that superseded the neat PLA and talc variant which both failed the horizontal burning test. The rheology of the composites provided evidence in the degradation of the PLA chains from the presence of the biocarbon that did not occur with the talc, which may have also contributed to the lower barrier and higher burn resistance from increased dripping. Thus, both talc and biocarbon have their own potential applicability when it comes to acting as a barrier enhancer or flammability retardant due to their intrinsic nature, but both possess wear reinforcement for focus in the tribological area.

Mechanical, thermal, and morphological properties of PLA biocomposites toughened with silylated bamboo cellulose nanowhiskers

To improve the surface compatibility between hydrophobic poly(lactic acid) (PLA) and hydrophilic bamboo cellulose nanowhiskers (BCNWs), four commercial available silane coupling agents were employed to modify their interfaces with different concentrations (0, 1, 8, and 16 wt%). PLA/BCNW biocomposite films were fabricated by solution casting. The effects of silylated BCNW on the thermal, mechanical, and morphological properties of PLA biocomposites were investigated. The coupled reaction between coupling agents and cellulose via Si‐O‐C bonding and hydrogen bonding was confirmed. Both, tensile strength and tensile modulus, decreased with the four silane treatments. The maximum elongation at break values increased to 213.8, 111.3, 255.3, and 209.8% after 16 wt% A‐151, 8 wt% A‐1100, 8 wt% A‐174, and 8 wt% A‐189 silane treatments, respectively, with respect to 12.4% of the untreated composite. A wire‐drawing phenomenon was observed on the tensile fractural surface. Glass transition temperature and crystallinity decreased after the surface modifications. POLYM. COMPOS., 40:3012–3019, 2019. © 2018 Society of Plastics Engineers

Evaluation of the Rosemary Extract Effect on the Properties of Polylactic Acid-Based Materials.

New multifunctional materials containing additives derived from natural resources as powdered rosemary ethanolic extract were obtained by melt mixing and processed in good conditions without degradation and loss of additives. Incorporation of powdered rosemary ethanolic extract (R) into poly(lactic acid) (PLA) improved elongation at break, rheological properties, antibacterial and antioxidant activities, in addition to the biocompatibility. The good accordance between results of the chemiluminescence method and radical scavenging activity determination by chemical method evidenced the increased thermoxidative stability of the PLA biocomposites with respect to neat PLA, with R acting as an antioxidant. PLA/R biocomposites also showed low permeability to gases and migration rates of the bioactive compounds and could be considered as high-performance materials for food packaging. In vitro biocompatibility based on the determination of surface properties demonstrated a good hydrophilicity, better spreading and division of fibroblasts, and increased platelet cohesion. The implantation of PLA/R pellets, was proven to possess a good in vivo biocompatibility, and resulted in similar changes in blood parameters and biochemical responses with the control group, suggesting that these PLA-based materials demonstrate very desirable properties as potential biomaterials, useful in human medicine for tissue engineering, wound management, orthopedic devices, scaffolds, drug delivery systems, etc. Therefore, PLA/R-based materials show promising properties for applications both in food packaging and as bioactive biomaterials.