Fungal biodegradation of poly(butylene adipate-co-terephthalate)-polylactic acid-thermoplastic starch based commercial bio-plastic film at ambient conditions

Microbial biodegradation of commercially available poly(butylene adipate-co-terephthalate)-polylactic acid-thermoplastic starch based bio-plastic has been pursued at high temperatures exceeding 55 °C. Herein, we first reported three newly isolated fungal strains from farmland soil samples of Republic of Korea namely, Pyrenochaetopsis sp. strain K2, Staphylotrichum sp. S2-1, and Humicola sp. strain S2-3 were capable of degrading a commercial bio-plastic film with degradation rates of 9.5, 8.6, and 12.2%, respectively after 3 months incubation at ambient conditions. Scanning electron microscopy (SEM) analyses showed that bio-plastic film was extensively fragmented with severe cracking on the surface structure after incubation with isolated fungal strains. X-ray diffraction (XRD) analysis also revealed that high crystallinity of the commercial bio-plastic film was significantly decreased after degradation by fungal strains. Liquid chromatography-mass spectrometry (LC-MS) analyses of the fungal culture supernatants containing the bio-plastic film showed the peaks for adipic acid, terephthalic acid (TPA), and terephthalate-butylene (TB) as major metabolites, suggesting cleavage of ester bonds and accumulation of TPA. Furthermore, a consortium of fungal strain K2 with TPA degrading bacterium Pigmentiphaga sp. strain P3-2 isolated from the same sampling site exhibited faster degradation rate of the bio-plastic film within 1 month of incubation with achieving complete biodegradation of accumulated TPA. We assume that the extracellular lipase activity presented in the fungal cultures could hydrolyze the ester bonds of PBAT component of bio-plastic film. Taken together, the fungal and bacterial consortium investigated herein could be beneficial for efficient biodegradation of the commercial bio-plastic film at ambient conditions.

Biaxial Orientation of PLA/PBAT/Thermoplastic Cereal Flour Sheets: Structure-Processing-Property Relationships

This paper investigates the biaxial stretchability of polylactic acid (PLA)/poly (butylene adipate co-terephthalate) (PBAT)/thermoplastic cereal flour (TCF) ternary blends with a PLA/PBAT ratio close to 60/40 and a constant TCF content. A twin-screw extrusion process was used to gelatinize the starch and devolatilize the water in order to obtain a water-free TCF, which was then blended into a compatibilized or non-compatibilized PLA/PBAT matrix, introduced in the molten state. These blends were subsequently cast into sheets and biaxially drawn using a biaxial laboratory stretcher. The prepared ternary blends were found to present a typical ductile behavior. Scanning electron micrography highlighted dispersion and adhesion properties in the PLA/PBAT/TCF blends, where two different phases were observed. Moreover, the addition of the thermoplastic cereal flour did not significantly affect the biaxial stretchability of the PLA/PBAT blends but was found to lower the maximum stress before breaking. The modification of the interfacial tension between PLA and PBAT with the compatibilizer Joncryl before mixing with TCF had no effect on the durability of the PLA/PBAT/TCF sheet. Still, it slightly increased the maximum of nominal stress before failure.

Relationship between microstructure and performances of simultaneous biaxially stretched films based on thermoplastic starch and biodegradable polyesters

Although thermoplastic starch (TPS) is a good candidate to overcome the limitations of poly(lactic acid) (PLA) due to its relatively low cost and high flexibility, the toughness and barrier properties of PLA/TPS blends are still insufficient for film applications. Therefore, the present work aims to improve the performance of PLA/TPS blend by simultaneous biaxial stretching and partially replacing PLA with poly(butylene adipate-co-terephthalate) (PBAT) for packaging film applications. PLA/TPS and PLA/PBAT/TPS sheets were prepared by melt cast extrusion and simultaneously biaxially stretched to form films. The mechanical, morphological, thermal, and water vapor and oxygen barrier properties and crystallinity of both intermediate sheets and their corresponding stretched films were examined. After stretching, PLA/TPS and PLA/PBAT/TPS blends showed markedly improved extensibility, impact strength, crystallinity, water vapor and oxygen barrier properties, and surface hydrophobicity. The stretched films demonstrated stacked-layer planar morphology, in which their outermost layers were a biodegradable polyester-rich phase. The synergistic effects of simultaneous biaxial stretching and partial replacing PLA with PBAT were extremely impressive for toughness improvement. The stretched films have the potential to replace non-biodegradable plastic packaging films, particularly where good mechanical and barrier properties are required.

Optimisation on Thermoforming of Biodegradable Poly (Lactic Acid) (PLA) by Numerical Modelling

Poly (lactic acid) (PLA) has a broad perspective for manufacturing green thermoplastic products by thermoforming for its biodegradable properties. The mechanical behaviour of PLA has been demonstrated by its strong dependence on temperature and strain rate at biaxial deformation. A nonlinear viscoelastic model by the previous study was employed in a thermoforming process used for food packaging. An optimisation approach was developed by achieving the optimal temperature profile of specimens by defining multiple heating zones based on numerical modelling with finite element analysis (FEA). The forming process of a PLA product was illustrated by modelling results on shape evolution and biaxial strain history. The optimal temperature profile was suggested in scalloped zones to achieve more even thickness distribution. The sensitivity of the optimal results was addressed by checking the robustness under perturbation.

Poly (lactic acid) blends: Processing, properties and applications

Poly (lactic acid) or polylactide (PLA) is a commercial biobased, biodegradable, biocompatible, compostable and non-toxic polymer that has competitive material and processing costs and desirable mechanical properties. Thereby, it can be considered favorably for biomedical applications and as the most promising substitute for petroleum-based polymers in a wide range of commodity and engineering applications. However, PLA has some significant shortcomings such as low melt strength, slow crystallization rate, poor processability, high brittleness, low toughness, and low service temperature, which limit its applications. To overcome these limitations, blending PLA with other polymers is an inexpensive approach that could also tailor the final properties of PLA-based products. During the last two decades, researchers investigated the synthesis, processing, properties, and development of various PLA-based blend systems including miscible blends of poly l-lactide (PLLA) and poly d-lactide (PDLA), which generate stereocomplex crystals, binary immiscible/miscible blends of PLA with other thermoplastics, multifunctional ternary blends using a third polymer or fillers such as nanoparticles, as well as PLA-based blend foam systems. This article reviews all these investigations and compares the syntheses/processing-morphology-properties interrelationships in PLA-based blends developed so far for various applications.

Structural Evolution of Two-Phase Blends of Polycarbonate and PMMA by Simultaneous Biaxial Stretching

We investigated the structural evolution of the two-phase blends of polycarbonate (PC) and poly(methyl methacrylate) (PMMA) at various blend compositions by simultaneous biaxial stretching, using optical microscopy and SEM observation. The spherical PMMA domains and PC matrix of 30/70 PC/PMMA were enlarged uniformly at the all in-plane direction, while the anisotropic-shaped co-continuous structure in 50/50 PC/PMMA was deformed to a crosshatched structure by the in-plane bimodal orientation. In 70/30 PC/PMMA, the phase inversion was found to occur by simultaneous biaxial stretching; that is, the spherical PMMA domains were changed to a crosshatched matrix by the in-plane bimodal orientation due to coalescence of the PMMA domains during the stretching. Owing to the phase inversion, the surface hardness estimated by the pencil hardness test became harder, from 2B to 2H, increasing the strain from 1.0 to 2.0.

Rheology, thermal properties, and foaming behavior of high d-content polylactic acid/cellulose nanofiber composites

Cellulose nanofibers (CNFs) substantially improved the foam structure of a high d-content PLA by enhancing its melt strength and crystallization kinetics and serving as effective heterogeneous cell-nucleating agents.

Obtaining a Flexible Film Elaborated from Cassava Thermoplastic Starch and Polylactic Acid

A flexible film was obtained from a blend of cassava thermoplastic starch and polylactic acid, using maleic anhydride as coupling agent. For this, an experimental design with three factors was used: polylactic acid content, coupling agent content, and temperature profile of the blown extrusion. It was found that the three factors generated significant differences on the response variables of tensile mechanical properties individually as in their triple interaction. Differential scanning calorimetry (DSC) was used by understanding the behavior of thermal properties of TPS/PLA blends with and without coupling agent, finding similar results between both. From this, the combination with 28% polylactic acid, 0.87% coupling agent, and 155.75°C temperature profile permitted the obtaining of a material with outstanding mechanical properties and offered advantages from the economic point of view.

Crystallization of PLA/Thermoplastic Starch Blends

In this paper, the crystallization of PLA in PLA/thermoplastic starch (TPS) blends was investigated. The TPS was used as the minor component at a concentration varying between 0 and 42 %. The effect of interfacial area was studied by compatibilizing the blend using maleic anhydride grafted PLA. To further enhance the crystallization rate in PLA/TPS blends, the addition of talc and acetyl triethyl citrate, as nucleating agent and plasticizer respectively, was also studied. The crystallization rate was monitored using DSC analysis under both isothermal and non- isothermal conditions. The isothermal data was used to determine the crystallization half-life and to determine the optimum crystallization temperature. The crystallization half-time of PLA was decreased significantly in presence of the TPS phase and this effect was strengthened by the blends interfacial modification. By applying proper plasticization and nucleation strategy, crystallinity in excess of 50 % was achieved even at cooling rates as high as 80°C/min. Fully crystallized PLA/TPS samples were obtained by injection molding in a hot mold (80°C). Crystallized parts showed improved thermal resistance at temperatures above PLA's glass transition.

The foamability of low-melt-strength linear polypropylene with nanoclay and coupling agent

In this work, the feasibility of producing microcellular foam by using homopolymer linear polypropylene with an melt flow index of 18 g/10 min, a high melt flow index coupling agent (G3003, melt flow index of 380 g/min), and different nanoclay (Cloisite 20A) content was investigated. A twin-screw extruder was used to prepare the nanocomposite compounds, and an X-ray diffraction machine was used to characterize the intercalation and exfoliation of nanoclay within the matrix. A rheology test was undertaken to investigate the melt shear viscosity of the samples. A single-screw extruder was employed to produce foam by using 5% supercritical CO2 at various die temperatures. Scanning electron microscopy was used to explore the morphology of the foamed samples, and cell density was calculated by scanning electron microscopy images. Density measurement data was used to calculate the expansion ratio of the foamed samples. Extrusion foaming produced foams with high expansion ratios of about 20 and a high cell density of about 108−9 cells/cm3. The crystallinity behavior of the foamed and unfoamed linear polypropylene and linear polypropylene nanocomposites was also investigated. A high-pressure differential scanning calorimetry was used to investigate the dependency of crystallization behavior on high pressure CO2.

A study of the crystallization, melting, and foaming behaviors of polylactic acid in compressed CO₂

The crystallization and melting behaviors of linear polylactic acid (PLA) treated by compressed CO(2) was investigated. The isothermal crystallization test indicated that while PLA exhibited very low crystallization kinetics under atmospheric pressure, CO(2) exposure significantly increased PLA's crystallization rate; a high crystallinity of 16.5% was achieved after CO(2) treatment for only 1 min at 100 degrees C and 6.89 MPa. One melting peak could be found in the DSC curve, and this exhibited a slight dependency on treatment times, temperatures, and pressures. PLA samples tended to foam during the gas release process, and a foaming window as a function of time and temperature was established. Based on the foaming window, crystallinity, and cell morphology, it was found that foaming clearly reduced the needed time for PLA's crystallization equilibrium.