Photodegradation and Biodegradation Study of a Starch and Poly(Lactic Acid) Coextruded Material

To simulate the behavior of agricultural mulch coextruded poly(lactic acid)(PLA)/starch films, two stages were carried out. The first was an ultraviolet treatment (UV) at 315 nm, during which glass transition temperature T_g, weight, and molecular weight (MW) decreased and a separation between PLA and starch phase was observed. For the second stage, the mineralization of the carbon of the material was followed using the ASTM (D 5209–92 and 5338–92) and ISO/CEN (14852 and 14855) standard procedures. To measure the biodegradability of polymer material, the assessment of the carbon balance allowed determination of the distribution between the carbon rate used to the biomass synthesis or the respiration process (released CO₂), as well as the dissolved organic carbon into the culture medium and the carbon in the residual insoluble material. The influence of the nature of the medium and the standardized procedures on the final rate of biodegradation was investigated. Whatever the standardized method, the biodegradation percentage was significantly stronger in liquid medium (92.4–93.4) than on inert medium (80–83%). In the case of the compost process, only released CO₂ was measured and corresponded to 79.1–80.3%.     

Mechanical and Barrier Properties of Biodegradable Films Made from Chitosan and Poly (Lactic Acid) Blends

Biodegradable film blends of chitosan with poly(lactic acid) (PLA) were prepared by solution mixing and film casting. The main goal of these blends is to improve the water vapor barrier of chitosan by blending it with a hydrophobic biodegradable polymer from renewable resources. Mechanical properties of obtained films were assessed by tensile test. Thermal properties, water barrier properties, and water sensitivity were studied by differential scanning calorimeter analysis, water vapor permeability measurements, and surface-angle contact tests, respectively. The incorporation of PLA to chitosan improved the water barrier properties and decreased the water sensitivity of chitosan film. However, the tensile strength and elastic modulus of chitosan decreased with the addition of PLA. Mechanical and thermal properties revealed that chitosan and PLA blends are incompatible, consistent with the results of Fourier transform infrared (FTIR) analysis that showed the absence of specific interaction between chitosan and PLA.     

Thermal and Rheological Properties of Commercial-Grade Poly(Lactic Acid)s

Poly(lactic acid) is the subject of considerable commercial development by a variety of organizations around the world. In this work, the thermal and rheological properties of two commercial-grade poly(lactic acid)s (PLAs) are investigated. A comparison of the commercial samples to a series of well-defined linear and star architecture PLAs provides considerable insight into their flow properties. Such insights are valuable in deciding processing strategies for these newly emerging, commercially significant, biodegradable plastics. Both a branched and linear grade of PLA are investigated. The crystallization kinetics of the branched polymer are inferred to be faster than the linear analog. Longer relaxation times in the terminal region for the branched material compared to the linear material manifests itself as a higher zero shear rate viscosity. However, the branched material shear thins more strongly, resulting in a lower value of viscosity at high shear rates. Comparison of the linear viscoelastic spectra of the branched material with the spectra for star PLAs suggests that the branched architecture is characterized by a span molecular weight of approximately 63,000 g/mol. The present study conclusively demonstrates that a wide spectrum of flow properties are available through simple architectural modification of PLA, thus allowing the utilization of this important degradable thermoplastic in a variety of processing operations.     

Starch, Poly(lactic acid), and Poly(vinyl alcohol) Blends

Research on biodegradable materials has been stimulated due to concern regarding the persistence of plastic wastes. Blending starch with poly(lactic acid) (PLA) is one of the most promising efforts because starch is an abundant and cheap biopolymer and PLA is biodegradable with good mechanical properties. Poly(vinyl alcohol) (PVOH) contains unhydrolytic residual groups of poly(vinyl acetate) and also has good compatibility with starch. It was added to a starch and PLA blend (50:50, w/w) to enhance compatibility and improve mechanical properties. PVOH (M_W 6,000) at 10%, 20%, 30%, 40%, 50% (by weight) based on the total weight of starch and PLA, and 30% PVOH at various molecular weights (M_W 6,000, 25,000, 78,000, and 125,000 dalton) were added to starch/PLA blends. PVOH interacted with starch. At proportions greater than 30%, PVOH form a continuous phase with starch. Tensile strength of the starch/PLA blends increased as PVOH concentration increased up to 40% and decreased as PVOH molecular weight increased. The increasing molecular weight of PVOH slightly affected water absorption, but increasing PVOH concentration to 40% or 50% increased water absorption. Effects of moisture content on the starch/PLA/PVOH blend also were explored. The blend containing gelatinized starch had higher tensile strength. However, gelatinized starch also resulted in increased water absorption.     

A Literature Review of Poly(Lactic Acid)

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.     

Biodegradable Blends Based on Starch and Poly(Lactic Acid): Comparison of Different Strategies and Estimate of Compatibilization

Finding plastic substitutes based on sustainability, especially for short-term packaging and disposable applications has aroused scientific interest for many years. Starch may be a substitute for petroleum based plastics but it shows severe limitations due to its water sensitivity and rather low mechanical properties. To overcome these weaknesses and to maintain the material biodegradability, one option is to blend plasticized starch with another biodegradable polymer. To improve both the compatibility between the main phases and the performance of the final blend, different compatibilization strategies are reported in literature. However, the relative efficiency of each strategy is not widely reported. This paper presents three different strategies: in situ (i) formation of urethane linkages; (ii) coupling with peroxide between starch and PLA, and (iiii) the addition of PLA-grafted amylose (A-g-PLA) which has been elaborated ex situ and carefully analyzed before blending. This study compares the effect of each compatibilization strategy by investigating mechanical and thermal properties of each blend. Compatibilizing behavior of the A-g-PLA is demonstrated, with a significant increase (up to 60%) in tensile strength of starch/PLA blend with no decrease in elongation at failure.     

Properties of Starch/PVA Blend Films Containing Citric Acid as Additive

Starch/polyvinyl alcohol (PVA) blend films were prepared successfully by using starch, polyvinyl alcohol (PVA), glycerol (GL) sorbitol (SO) and citric acid (CA) for the mixing process. The influence of mixing time, additional materials and drying temperature of films on the properties of the films was investigated. With increase in mixing time, the tensile strength (TS), elongation (%E), degree of swelling (DS) and solubility (S) of the film were equilibrated. The equilibrium for TS, %E, DS and S value was 20.12 MPa, 36.98%, 2.4 and 0.19, respectively. The mixing time of equilibrium was 50 min. TS, %E, DS and S of starch/PVA blend film were examined adding glycerol (GL), sorbitol (SO) and citric acid (CA) as additives. At all measurement results, except for DS, the film adding CA was better than GL or SO because hydrogen bonding at the presence of CA with hydroxyl group and carboxyl group increased the inter/intramolecular interaction between starch, PVA and additives. Citric acid improves the properties of starch/PVA blend film compared to glycerol and sobitol. When the film was dried at low temperature, the properties of the films were clearly improved because the hydrogen bonding was activated at low temperature.     

Effects of Diisocyanate and Polymeric Epoxidized Chain Extenders on the Properties of Recycled Poly(Lactic Acid)

Increasing demand in the use of poly(lactic acid) (PLA) leads to a debate about using potential foodstuffs for plastic production and a moral issue when starvation problem is taken into account. One of the solutions is recycling of PLA; however, recycling results in property losses during melt processing due to low thermal stability of PLA. This study focuses on using chain extenders to offset thermal degradation of recycled PLA. The effects of a diisocyanate and a polymeric epoxidized chain extender on the properties of the recycled poly(lactic acid) were investigated. In order to mimic the recycling process, PLA was subjected to thermo-mechanical degradation using a laboratory scale compounder. Chain extender type, loading and mixing time were investigated. On-line rheology and intrinsic viscosity measurements of PLA before and after chain extension confirmed that the molecular weight increased. Dynamic mechanical analysis, rheology and tensile tests revealed that the chain extenders led to a significant increase in modulus, strength and melt-viscosity. It was found that diisocyanate had slightly higher and faster chain extension reactivity than polymeric extender. Differential scanning calorimetry results showed an increase in the crystallization temperature due to the branched and extended chain structure.     

Thermal and mechanical properties of poly(lactic Acid) and poly(ethylene/butylene Succinate) blends

In this study, blends of poly (lactic acid) (PLA) with poly(ethylene/butylene succinate) (Bionolle) have been investigated for their thermal and mechanical properties as a function of the concentration of Bionolle. Differential scanning calorimetry (DSC), dynamic mechanical analysis (DMA), and tensile tests were used to characterize the blends. From the results of the DMA and DSC, it was found that this blend system was not miscible within the compositions studied. DSC results showed that adding Bionolle aids in crystallization of PLA. It was observed that increasing the Bionolle concentration led to a slight increase in the strain-at-break of the blends but a decrease in the Young’s modulus and ultimate tensile strength. Biaxially oriented films showed an increase in tensile strength, modulus, and strain-at-break.     

The Effect of Nanoclays on the Properties of PLLA-modified Polymers Part 1: Mechanical and Thermal Properties

Organically modified montmorillonite clays were incorporated at a 5% loading level into film grade of poly-L-lactic acid (PLLA) using a variety of masterbatches based on either semi-crystalline or amorphous poly-(lactic acid), as well as biodegradable aromatic aliphatic polyester. The PLLA masterbatches and compounded formulations were prepared using a twin screw compounding extruder, while the films were prepared using a single screw cast film extruder. The thermal and mechanical properties of the films were examined in order to determine the effect of the clay and different carriers on the polymer–clay interactions. In the optimal case, when a PLLA-based masterbatch was used, the tensile modulus increased by 30%, elongation increased by 40%, and the cold crystallization temperature decreased by 15 °C, compared to neat PLLA. The properties improvement of PLLA films containing nano clays demonstrated the possibility to extend the range of biodegradable film applications, especially in the field of packaging.     

Mechanical Property Characterization of Plasticized Sugar Beet Pulp and Poly(Lactic Acid) Green Composites Using Acoustic Emission and Confocal Microscopy

Sorbitol and glycerol were used to plasticize sugar beet pulp-poly(lactic acid) green composites. The plasticizer was incorporated into sugar beet pulp (SBP) at 0%, 10%, 20%, 30% and 40% w/w at low temperature and shear and then compounded with poly(lactic acid) (PLA) using twin-screw extrusion and injection molding. The SBP:PLA ratio was maintained at 30:70. As expected, tensile strength decreased by 25% and the elongation increased. Acoustic emission (AE) showed correlated debonding and fracture mechanisms for up to 20% w/w plasticizer and uncorrelated debonding and fracture for 30–40% sorbitol and 30% glycerol content in SBP–PLA composites. All samples had a well dispersed SBP phase with some aggregation in the PLA matrix. However, at 40% glycerol plasticized SBP–PLA composites exhibited unique AE behavior and confocal microscopy revealed the plasticized SBP and PLA formed a co-continuous two phase system.

The Effect of Masterbatch Addition on the Mechanical, Thermal, Optical and Surface Properties of Poly(lactic acid)

There has been considerable interest in the use of the biodegradable polymer poly(lactic acid) (PLA) as a replacement for petroleum derived polymers due to ease of processability and its high mechanical strength. Other material properties have however limited its wider application. These include its brittle properties, low impact strength and yellow tint. In an attempt to overcome these drawbacks, PLA was blended with four commercially available additives, commonly known as masterbatches. The effect of the addition of 1.5 wt% of the four masterbatches on the mechanical, thermal, optical and surface properties of the polymer was evaluated. All four masterbatches had a slight negative effect on the tensile strength of PLA (3–5% reduction). There was a four fold increase in impact resistance however with the addition of one of the masterbatches. Differential scanning calorimetry demonstrated that this increase corresponded to a decrease in the polymer crystallinity. However there was an associated increase in polymer haze with the addition of this masterbatch. The clarity of PLA was improved through the addition of an optical brightener masterbatch, but the impact resistance remained low. The glass transition and melting temperatures of PLA were not affected by the addition of the masterbatches, and no change was observed in surface energy. Some delay in PLA degradation, in a PBS degradation medium at 50 °C, was observed due to blending with these masterbatches.     

Physical Properties of Chemically Modified Starch(RS4)/PVA Blend Films—Part 1

In this paper, we report on the physical properties of films that have been synthesized by using native corn starch (NS) and chemically modified starch (RS4). NS or RS4/PVA blend films were synthesized by using the mixing process and the casting method. Glycerol (GL), sorbitol (SO), and citric acid (CA) were used as additives. The chemically modified starch (RS4) was synthesized by using sodium trimetaphosphate (STMP) and sodium tripolyphosphate (STPP) as a crosslinker. Then, the RS4 thus synthesized was confirmed by using the pancreatin-gravimetric method, swelling power and an X-ray diffractometer (XRD). Tensile strength (TS), elongation (%E), swelling behavior (SB), and solubility (S) of the films were measured. The result of the measurements indicated the RS4-added film was better than the NS-added film. Especially, the RS4/PVA blend film with CA as an additive showed the physical properties superior to other films.     

Microbial Poly(L-Lactide)-Degrading Enzyme Induced by Amino Acids, Peptides, and Poly(L-Amino Acids)

Poly(L-lactide)(PLA)-degrading activities of a fungus, Tritirachium album, and two strains of actinomycetes,Lentzea waywayandensis and Amycolatopsis orientalis, were inducible by some proteins (poly-L-amino acid), peptides and amino acids. Extracellular PLA-degrading activity of the culture filtrates was detected when these strains grew in liquid basal medium containing 0.1% (w/v) of (poly-L-amino acids), peptides or amino acids as the enzyme inducer. In addition to PLA-degrading activity, succinyl-(L-alanyl-L-alanyl-L-alanine)-p-nitroanilide (Suc-(Ala)₃-pNA)-degrading activity was observed, implying that the enzymes produced were protease-type. The enzyme activities produced varied between different strains and different inducers. Silk fibroin was the best inducer for A. orientalis and that elastin was the best inducer for L. waywayandensis and T. album.     

Effect of Poly(dioxolane) as Compatibilizer in Poly(ɛ-caprolactone)/Tapioca Starch Blends

The influence of poly(dioxolane) (PDXL), a poly(ethylene oxide-alt-methylene oxide), as compatibilizer on poly(ɛ-caprolactone) (PCL)/tapioca starch (TS) blends was studied. In order to facilitate blending; PCL, PDXL and TS must be blended together directly; so that PDXL is partially adhered at the TS surface as shown by scanning electron microscopy. The molecular weight effect of PDXL on the PCL/TS blends showed that mechanical properties of PCL/TS/PDXL blends from low molecular weight (M _n=10,000) and high molecular weight (M _n=200,000) PDXL were rather dependent on TS content. The enzymatic degradability of PCL/TS/PDXL blends using α-amylase increased as the TS content increased but was independent on the dispersion of tapioca starch in the PCL matrix.     

Physical Properties and Fiber Morphology of Poly(lactic acid) Obtained from Continuous Two-Step Melt Spinning

Fibers of poly(lactic acid) (PLA) produced by two-step melt-spinning are studied. The PLA resin used contains a 98:02 ratio of l:d stereochemical centers. A range of processing conditions is explored. The cold-draw ratio is varied from 1 to 8 under conditions of constant heating. In addition, three draw ratios are studied at three different heating rates. The thermal, mechanical, and morphological properties of the resultant fibers are determined. Properties can be widely manipulated through a combination of draw ratio and draw temperature. A maximum tensile strength and modulus of 0.38 GPa and 3.2 GPa, respectively, are obtainable. Using atomic force microscopy, the fiber morphology is found to be highly fibrillar; microfibril diameters are roughly 40 nm in diameter. Very high draw ratios cause the fiber to turn from shiny and translucent to dull and white; this transition is attributed to surface crazing. Significant molecular weight loss is observed upon processing (weight-average molecular weights drops between 27% and 43%).     

Preparation and Characterization of Gamma Irradiated Sugar Containing Starch/Poly (Vinyl Alcohol)-Based Blend Films

Blends based on different ratios of starch (35–20%) and plasticizer (sugar; 0–15%) keeping the amount of poly(vinyl alcohol) (PVA) constant, were prepared in the form of thin films by casting solutions. The effects of gamma-irradiation on thermal, mechanical, and morphological properties were investigated. The studies of mechanical properties showed improved tensile strength (TS) (9.61 MPa) and elongation at break (EB) (409%) of the starch-PVA-sugar blend film containing 10% sugar. The mechanical testing of the irradiated film (irradiated at 200 Krad radiation dose) showed higher TS but lower EB than that of the non-radiated film. FTIR spectroscopy studies supported the molecular interactions among starch, PVA, and sugar in the blend films, that was improved by irradiation. Thermal properties of the film were also improved due to irradiation and confirmed by thermo-mechanical analysis (TMA), differential thermo-gravimetric analysis (DTG), differential thermal analysis (DTA), and thermo-gravimetric analysis (TGA). Surface of the films were examined by scanning electron microscope (SEM) image that supported the evidence of crosslinking obtained after gamma irradiation on the film. The water up-take and degradation test in soil of the film were also evaluated. In this study, sugar acted as a good plasticizing agent in starch/PVA blend films, which was significantly improved by gamma radiation and the prepared starch-PVA-sugar blend film could be used as biodegradable packaging materials.     

Biodegradable Polymers from 5-Hydroxylevulinic Acid: 1. Synthesis and Characterization of Poly(5-hydroxylevulinic acid)

As an attempt to synthesize new biodegradable polymers from renewable cellulose resources, melt polycondensation of 5-hydroxylevulinic acid (5-HLA) was reported for the first time. The resulting product, poly(5-hydroxylevulinic acid) (PHLA), was synthesized and characterized with GPC, FTIR, ¹H NMR and DSC. The in vitro degradation behaviors in phosphate-buffered saline (PBS) and in deionized water (DW) were also examined. The molecular weight of PHLA is not high (several 1,000s), but it possesses unordinary high glass transition temperature (as high as 120 °C). This is very different from existing aliphatic polyesters that usually have T _gs lower than 60 °C. The high T _g is attributed to the formation of inter- and/or intramolecular hydrogen bonds due to a characteristic keto–enol tautomerism equilibrium in the polymer structure. PHLA readily degraded hydrolytically in aqueous media.     

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%.     

Enzymatic Degradation of Poly(l-Lactic Acid): Effects of UV Irradiation

Amorphous and crystallized poly(l-lactic acid) (PLLA-A and PLLA-C, respectively) films were prepared, and the proteinase K-catalyzed enzymatic degradation of UV-irradiated and non-irradiated PLLA-A and PLLA-C films was investigated for periods up to 10 h (PLLA-A) and 60 h (PLLA-C). The molecular weights of both the PLLA-A and PLLA-C films can be manipulated by altering the UV irradiation time. The enzymatic weight loss values of the UV-irradiated PLLA films were higher than or similar to those of the non-irradiated PLLA film, when compared with the specimens of same crystallinities. UV irradiation is expected to cause the PLLA films to undergo chain cleavage (a decrease in molecular weight) and the formation of C=C double bonds. It seems that the acceleration effects from decreased molecular weight on enzymatic degradation were higher than or balanced with the disturbance effects caused by the formation of C=C double bonds. After enzymatic degradation, a fibrous structure appeared on the spherulites of the UV-irradiated PLLA-C film. This structure may have arisen from chains containing or neighboring on the C=C double bonds, which were enzymatically undegraded and assembled on the film surface during enzymatic degradation. The results of this study strongly suggest that UV irradiation will significantly affect the biodegradation behavior of PLLA materials in the environment.