Biodegradation of Polylactic Acid-Based Bio Composites Reinforced with Chitosan and Essential Oils as Anti-Microbial Material for Food Packaging

Multifunctional polylactic acid biocomposite film for active food packaging with UV resistance, antioxidant and antibacterial properties

Antibacterial packaging used to control the growth of microorganisms in food is of great value for prolonging the shelf life of food. In this study, a bio-based antibacterial agent PDI based on zwitterionic and stereochemical synergistic antibacterial was designed and synthesized, and it was simultaneously introduced into polylactic acid (PLA) matrix with antioxidant o-vanillin (oVL) and plasticizer glycerol (GL). A series of PLA/oVL/PDI composite membranes with antibacterial, antioxidant and anti-ultraviolet properties were prepared by solution casting method. The results showed that the mechanical properties of the composite film were significantly improved compared with pure PLA (tensile strength increased by 37 %, elongation at break increased by 209 %), which was mainly attributed to the microphase separation structure induced by synthetic bio-based antibacterial agent, which improved the mechanical strength of PLA matrix, and the hydrogen bond formed by glycerol, o-vanillin and carbonyl group in PLA molecules plasticized PLA matrix. At the same time, the antibacterial rate of PLA/oVL/PDI composite membrane against Escherichia coli and Staphylococcus aureus can reach >95 %. Packaging experiments showed that PLA/oVL/PDI series composite films could effectively extend the shelf life of fresh bananas and apples for 5 days, and had great application prospects in preservative food packaging.

Phase Morphology, Mechanical, and Thermal Properties of Calcium Carbonate-Reinforced Poly(L-lactide)-b-poly(ethylene glycol)-b-poly(L-lactide) Bioplastics

Poly(L-lactide) (PLLA) is a promising candidate as a bioplastic because of its non-toxicity and biodegradability. However, the low flexibility of PLLA limits its use in many applications. Poly(L-lactide)-b-poly(ethylene glycol)-b-poly(L-lactide) (PLLA-b-PEG-b-PLLA) block copolymer is of interest for bioplastic applications due to its superior flexibility compared to PLLA. The aim of this work is to modify PLLA-b-PEG-b-PLLA using a low-cost calcium carbonate (CaCO₃) filler to improve material properties compared to PLLA/CaCO₃ composites. The addition of CaCO₃ enhanced the crystallinity and thermal stability for the PLLA-b-PEG-b-PLLA matrix but not for the PLLA matrix, as determined by differential scanning calorimetry (DSC), X-ray diffractometry (XRD), and thermogravimetric analysis (TGA). Phase morphology investigation using scanning electron microscopy (SEM) revealed that the interfacial adhesion between PLLA-b-PEG-b-PLLA and CaCO₃ was stronger than between PLLA and CaCO₃. Additionally, tensile testing was carried out to determine the mechanical properties of the composites. With the addition of CaCO₃, the tensile stress and Young's modulus of the PLLA-b-PEG-b-PLLA matrix were increased, whereas these properties of the PLLA matrix were significantly decreased. Thus, CaCO₃ shows great promise as an inexpensive filler that can induce nucleation and reinforcing effects for PLLA-b-PEG-b-PLLA bioplastics.

Enhancement in Crystallizability of Poly(L-Lactide) Using Stereocomplex-Polylactide Powder as a Nucleating Agent

High-molecular-weight poly(L-lactide) (HMW-PLLA) is a promising candidate for use as a bioplastic because of its biodegradability and compostability. However, the applications of HMW-PLLA have been limited due to its poor crystallizability. In this work, stereocomplex polylactide (scPLA) powder was prepared by precipitation of a low-molecular-weight poly(L-lactide)/poly(D-lactide) (LMW-PLLA/LMW-PDLA) blend solution and investigated for use as a fully-biodegradable nucleating agent for HMW-PLLA compared to LMW-PLLA powder. The obtained LMW-PLLA and scPLA powders with a nearly spherical shape showed complete homo- and stereocomplex crystallites, respectively. HMW-PLLA/LMW-PLLA powder and HMW-PLLA/scPLA powder blends were prepared by melt blending. The LMW-PLLA powder was homogeneously melted in the HMW-PLLA matrices, whereas the scPLA powder had good phase compatibility and was well-dispersed in the HMW-PLLA matrices, as detected by scanning electron microscopy (SEM). It was shown that the enthalpies of crystallization (ΔHc) upon cooling scans for HMW-PLLA largely increased and the half crystallization time (t1/2) dramatically decreased as the scPLA powder content increased; however, the LMW-PLLA powder did not exhibit the same behavior, as determined by differential scanning calorimetry (DSC). The crystallinity content of the HMW-PLLA/scPLA powder blends significantly increased as the scPLA powder content increased, as determined by DSC and X-ray diffractometry (XRD). In conclusion, the fully biodegradable scPLA powder showed good potential for use as an effective nucleating agent to improve the crystallization properties of the HMW-PLLA bioplastic.

Improvement in Thermal Stability of Flexible Poly(L-lactide)-b-poly(ethylene glycol)-b-poly(L-lactide) Bioplastic by Blending with Native Cassava Starch

High-molecular-weight poly(L-lactide)-b-poly(ethylene glycol)-b-poly(L-lactide) triblock copolymer (PLLA-PEG-PLLA) is a promising candidate for use as a biodegradable bioplastic because of its high flexibility. However, the applications of PLLA-PEG-PLLA have been limited due to its high cost and poor thermal stability compared to PLLA. In this work, native cassava starch was blended to reduce the production cost and to improve the thermal stability of PLLA-PEG-PLLA. The starch interacted with PEG middle blocks to increase the thermal stability of the PLLA-PEG-PLLA matrix and to enhance phase adhesion between the PLLA-PEG-PLLA matrix and dispersed starch particles. Tensile stress and strain at break of PLLA-PEG-PLLA films decreased and the hydrophilicity increased as the starch content increased. However, all the PLLA-PEG-PLLA/starch films remained more flexible than the pure PLLA film, representing a promising candidate in biomedical, packaging and agricultural applications.

Carbon Fiber/PLA Recycled Composite

Due exceptional properties such as its high-temperature resistance, mechanical characteristics, and relatively lower price, the demand for carbon fiber has been increasing over the past years. The widespread use of carbon-fiber-reinforced polymers or plastics (CFRP) has attracted many industries. However, on the other hand, the increasing demand for carbon fibers has created a waste recycling problem that must be overcome. In this context, increasing plastic waste from the new 3D printing technology has been increased, contributing to a greater need for recycling efforts. This research aims to produce a recycled composite made from different carbon fiber leftover resources to reinforce the increasing waste of Polylactic acid (PLA) as a promising solution to the growing demand for both materials. Two types of leftover carbon fiber waste from domestic industries are handled: carbon fiber waste (CF) and carbon fiber-reinforced composite (CFRP). Two strategies are adopted to produce the recycled composite material, mixing PLA waste with CF one time and with CFRP the second time. The recycled composites are tested under tensile test conditions to investigate the impact of the waste carbon reinforcement on PLA properties. Additionally, thermogravimetric analysis (TGA), X-ray diffraction (XRD), and Fourier-transformed infrared spectroscopy (FTIR) is carried out on composites to study their thermal properties.