Toughening and thermal characteristics of plasticized polylactide and poly(butylene adipate-co-terephthalate) blend films: Influence of compatibilization

Enhanced mechanical and long-lasting antibacterial properties of starch/PBAT blown films via designing of reactive micro-crosslinked starch

A functional starch (TPS-E) was designed and constructed by incorporating epoxy soybean oil (ESO) and an antibacterial agent polyhexamethylene guanidine hydrochloride (PHMG), then the film was prepared by reaction extrusion and blow molding using TPS-E and poly(butylene adipate-co-terephthalate) (PBAT). The micro-crosslinking structure, forming through ring-opening reaction between the epoxy active site of TPS-E and the end group of PBAT, improved the compatibility of starch/PBAT blend and reduce the dispersed starch phase size, leading to significantly increase the tensile strength. Compared to starch/PBAT films, the tensile strength of TPS-E/PBAT in the longitudinal direction increase by 112% with the same starch content of 30%. Furthermore, these TPS-E/PBAT films demonstrated long-lasting antibacterial performance with a 98% inhibition ratio even after 10 cycles, without any observed leaching of the antibacterial agent, highlighting the high coupling efficiency of PHMG. TPS-E with the degradable ESO also promotes the degradation of PBAT. Thus, an important method of synergistic improving the mechanical, degradable and antibacterial properties of blown films through the design of reactive micro-crosslinked starch structures was established.

Cross-linked poly(ester urethane)/starch composite films with high starch content as sustainable food-packaging materials: Influence of cross-link density

This study focused on the development of cross-linked poly(ester urethane)/starch (PEUST) composites containing 50 wt% starch content for food-packaging materials. The NCO-terminated poly(caprolactone-urethane) prepolymer (PCUP) was first synthesized through bulk condensation. Then, low-moisture starch (0.21 wt%) and PCUP-based PEUST films were fabricated through an intensive extrusion process, followed by thermo-compression molding. The chemical structure of PCUP and PEUST was confirmed using Fourier transform infrared spectroscopy. Moreover, a comprehensive evaluation was conducted to assess the influence of cross-link density on the physicochemical properties of the composite films. The results showed that an increase in the cross-link density within the composites improved component compatibility and tensile strength but reduced crystallinity, water sensitivity, hydrolytic degradability, and water vapor permeability (WVP) of the films. In addition, the cytotoxicity tests were conducted to evaluate the safety of the composite films, and the high cell viability demonstrated non-toxicity for food application. The PEUST-II films with moderate cross-link density exhibited a suitable degradation rate (27.7 % weight loss at degradation for 140 d), optimal tensile properties (tensile strength at break: 12.4 MPa; elongation at break: 352 %), and low WVP (68.4 g/(m2⋅24h) at 30 % relative humidity). These characteristics make them highly promising as fresh-keeping food packaging.

Strong synergistic toughening and compatibilization enhancement of carbon nanotubes and multi-functional epoxy compatibilizer in high toughened polylactic acid (PLA)/poly (butylene adipate-co-terephthalate) (PBAT) blends

Different carbon nanotubes (CNTs) contents on high-toughness polylactic acid (PLA)/poly (butylene adipate-co-terephthalate) (PBAT) blends were prepared by one-step melt blending using multifunctional epoxy oligomers (ADR) as reactive compatibilizer. During reactive blending, the PLA or PBAT chains were grafted onto the CNTs by allowing the carboxyl or hydroxyl groups to react with epoxy groups and form a branched CNTs-based copolymer. The branched copolymer at the interface between PLA and PBAT was dispersed through emulsion to improve the polymer-polymer or polymer-nanoparticle entanglement between the molecular chains. Interfacial adhesion, interface layer stability, and system viscoelasticity and compatibility were improved as indicated by rheological curves and dynamic mechanical analysis. The strength and toughness of the sample were simultaneously improved by the addition of CNTs and ADR. The impact strength reached 35.3 kJ/m2, which was approximately 7 times that of the PLA/PBAT blend, and the tensile strength was also increased from 33.6 MPa to 42.8 MPa. The properties of PLA/PBAT blend synergistically modified by ADR and CNTs were obviously better than those of PLA/PBAT blend modified by ADR or CNTs. The toughening synergistic effect of ADR and CNTs on PLA/PBAT was observed with efficiency reaching 3.05. With the further understanding of the toughening mechanism, the branched CNTs-based copolymers and CNTs clusters induce a synergistic effect, which increased the interfacial adhesion and ability of energy dissipation and stress transmission.

Investigation of the Effect of Hybrid Nanofiller on the Mechanical Performance and Surface Properties of Bio-Based Polylactic Acid/Polyolefin Elastomer (PLA/POE) Blend

Polylactic acid has stood out among bio-based polymers for its usage in the food packaging industry and biomedical fields. Through the melt mixing process, the toughened poly(lactic) acid (PLA) was prepared with polyolefin elastomer (POE), incorporated via various ratios of nanoclay and a fixed amount of nanosilver particles (AgNPs). The correlation between the compatibility and morphology, mechanical properties, and surface roughness of samples with nanoclay was studied. The calculated surface tension and melt rheology confirmed the interfacial interaction demonstrated by droplet size, impact strength, and elongation at break. Each blend sample exhibited matrix-dispersed droplets, and the size of POE droplets steadily dropped with increasing nanoclay content, corresponding to the enhanced thermodynamic affinity between PLA and POE. Scanning electron microscopy (SEM) acknowledged that the inclusion of nanoclay in the PLA/POE blend ameliorated the mechanical performance by preferable localization in the interface of used components. The optimum value of elongation at break was acquired at about 32.44%, where the incorporation of 1 wt.% nanoclay led, respectively, to 171.4% and 24% enhancement rather than the PLA/POE blend with the composition of 80/20 and the virgin PLA. Similarly, the impact strength reached 3.46 ± 0.18 kJ m^-1 as the highest obtained amount, showing the proximity of 23% progress to the unfilled PLA/POE blend. Surface analysis indicated that adding nanoclay caused the augment of surface roughness from 23.78 ± 5.80 µm in the unfilled PLA/POE blend to 57.65 ± 18.2 µm in PLA/POE contained 3 wt.% nanoclay. Rheological measurements implied that organoclay resulted in the strengthening of melt viscosity as well as the rheological parameters such as storage modulus and loss modulus. Han plot further showed that the storage modulus is always higher than the loss modulus in all prepared PLA/POE nanocomposite samples, corresponding to the restriction of polymer chains mobility induced by the formation of strong molecular interaction between nanofillers and polymer chains.

Fabricating super tough polylactic acid based composites by interfacial compatibilization of imidazolium polyurethane modified carbon nanotubes

The interfacial compatibilization and dispersion of carbon nanotubes (CNTs) in incompatible poly(lactic acid)/poly(butylene terephthalate adipate) (PLA/PBAT) composites are key points for evaluating the performance of the composites. To address this, a novel compatibilizer, sulfonate imidazolium polyurethane (IPU) containing PLA and poly(1,4-butylene adipate) segments modified CNTs, employed in conjunction with multi-component epoxy chain extender (ADR) to toughen synergistically PLA/PBAT composites. The thermal stability, rheological behavior, morphology, and mechanical properties of PLA/PBAT composites were performed by TGA, DSC, dynamic rheometer, SEM, tensile, and notched Izod impact measure. Moreover, the elongation at break and notched Izod impact strength of PLA5/PBAT5/4C/0.4I composites achieved 341 % and 61.8 kJ/m² respectively, whose tensile strength was 33.7 MPa. The interfacial compatibilization and adhesion were enhanced because of the interface reaction catalyzed by IPU and the refined co-continuous phase structure. The CNTs non-covalently modified by IPU that bridged at the PBAT phase and interface transferred the stress into the matrix, prevented the development of microcracks, and absorbed impact fracture energy in the form of pull-out of the matrix, inducing shear yielding and plastic deformation. This new type of compatibilizer with modified CNTs is of great significance for realizing the high performance of PLA/PBAT composites.

In-situ reactive compatiblization modified poly(l-lactic acid) and poly (butylene adipate-co-terephthalate) blends with improved toughening and thermal characteristics

Triglycidyl isocyanurate (TGIC) with multifunctional epoxy is used for reactive compatibilization of Poly (l-lactic acid) (PLLA)/Poly (butylene adipate-co-terephthalate) (PBAT) blends. Interfacial tension, FTIR and SEM results show that TGIC has greater affinity and stronger reactivity with PBAT. The mixing sequence of PLLA/PBAT/TGIC blends has a significant impact on the compatibility. The TGIC and PBAT are reactive blended first, followed by the PLLA, which is most advantageous to produce a substantial amounts of branched copolymers PLLA-g-PBAT at the interface for the (PBAT/4%T) /PLLA blend. The considerable improvement of interfacial compatibility and the thickening of interfacial layer promote the stress transfer from the matrix to the dispersed PBAT phase. In comparison to PLLA/PBAT blend, the breaking elongation of (PBAT/4%T)/PLLA blend is raised by 25.6 times up to 164.2 % and the tensile strength is enhanced up to 32.1 MPa. The present work offers valuable perspectives on how to encourage the efficient application of reactive compatibilizers with epoxy groups in polyester blends.

Maleic Anhydride-Grafted PLA Preparation and Characteristics of Compatibilized PLA/PBSeT Blend Films

Poly(butylene sebacate-co-terephthalate) (PBSeT) is a biodegradable flexible polymer suitable for melt blending with other biodegradable polymers. Melt blending with a compatibilizer is a common strategy for increasing miscibility between polymers. In this study, PBSeT polyester was synthesized, and poly(lactic acid) (PLA) was blended with 25 wt% PBSeT by melt processing with 3–6 phr PLA-grafted maleic anhydride (PLA-g-MAH) compatibilizers. PLA-g-MAH enhanced the interfacial adhesion of the PLA/PBSeT blend, and their mechanical and morphological properties confirmed that the miscibility also increased. Adding more than 6 phr of PLA-g-MAH significantly improved the mechanical properties and accelerated the cold crystallization of the PLA/PBSeT blends. Furthermore, the thermal stabilities of the blends with PLA-g-MAH were slightly enhanced. PLA/PBSeT blends with and without PLA-g-MAH were not significantly different after 120 h, whereas all blends showed a more facilitated hydrolytic degradation rate than neat PLA. These findings indicate that PLA-g-MAH effectively improves PLA/PBSeT compatibility and can be applied in the packaging industry.

Process-Induced Morphology of Poly(Butylene Adipate Terephthalate)/Poly(Lactic Acid) Blown Extrusion Films Modified with Chain-Extending Cross-Linkers

Process-induced changes in the morphology of biodegradable polybutylene adipate terephthalate (PBAT) and polylactic acid (PLA) blends modified with various multifunctional chain-extending cross-linkers (CECLs) are presented. The morphology of unmodified and modified films produced with blown film extrusion is examined in an extrusion direction (ED) and a transverse direction (TD). While FTIR analysis showed only small peak shifts indicating that the CECLs modify the molecular weight of the PBAT/PLA blend, SEM investigations of the fracture surfaces of blown extrusion films revealed their significant effect on the morphology formed during the processing. Due to the combined shear and elongation deformation during blown film extrusion, rather spherical PLA islands were partly transformed into long fibrils, which tended to decay to chains of elliptical islands if cooled slowly. The CECL introduction into the blend changed the thickness of the PLA fibrils, modified the interface adhesion, and altered the deformation behavior of the PBAT matrix from brittle to ductile. The results proved that CECLs react selectively with PBAT, PLA, and their interface. Furthermore, the reactions of CECLs with PBAT/PLA induced by the processing depended on the deformation directions (ED and TD), thus resulting in further non-uniformities of blown extrusion films.

Novel colorimetric membranes based on polylactic acid-grafted-citrated methacrylated urethane (PLA-CMU) to monitor cod freshness

Halochromic agent is easy to fall off from the surface of colorimetric membranes during fish freshness monitoring, which would decay the test accuracy. In order to increase its anchoring, citrated methacrylated urethane (CMU) synthesized by using tributyl citrate, β-hydroxyethyl methacrylate and diphenyl-methane-diisocyanate as a halochromic agent was grafted on polylactic acid (PLA). The CMU grafted PLA (PLA-CMU) together with tetrabutylammonium chloride (TBAC) prepared colorimetric membranes via electrospinning. ¹H NMR and FTIR analysis showed successful bonding between CMU and PLA, and PLA-CMU grafting efficiency reached to the maximum value of 11.15%. Moreover, DSC confirmed that PLA-CMU existed low cold-crystallization temperature due to the excellent compatibility of CMU with PLA, which enhanced the anchoring of CMU effectively. Nanofiber-based PLA-CMU/TBAC colorimetric membrane enhanced the probability of molecules being captured due to its porous structure and large specific surface area. In addition, the increase in hydrophilicity of the membrane can provide a microenvironment for liquid phase reaction, exhibiting obvious color-changing sensitivity during cod freshness monitoring, from white color to light orange or pink with the deterioration of cod at 25 °C and 4 °C respectively. The results demonstrate PLA-CMU/TBAC colorimetric membranes would provide a simple and promising strategy for monitoring fish freshness.

Preparation of effective ultraviolet shielding poly (lactic acid)/poly (butylene adipate-co-terephthalate) degradable composite film using co-precipitation and hot-pressing method

Biodegradable poly (lactide) (PLA) and poly (butylene adipate-co-terephthalate) (PBAT) composite films were made by a co-precipitation and hot-pressing method. The property of composite films like the chemical interaction, phase morphology, mechanical properties, and thermal properties were studied. The Fourier transform infrared spectroscopy (FTIR) test manifested that there was a small amount of the transesterifications between the PBAT and PLA during hot pressing, which could improve the compatibility of the two phases. The tensile strength of the film only reduced by 7.4%, while the elongation at break was increased by 119.1% compared with PLA after adding 4%wt PBAT. The composite films showed a high Ultraviolet-visible (UV) light barrier property. The UV blocking rate of the composite after adding 4%wt PBAT was 6.95 times higher than that of pure PLA at 380 nm. The PLA/PBAT composite films with excellent thermal stability, satisfactory mechanical properties and UV-light barrier have high a possibility for an UV screening packaging application.

Comprehensive exploration of natural degradation of poly(lactic acid) blends in various degradation media: A review

Poly(lactic acid) (PLA), a bio-based polyester, has been extensively investigated in the recent past owing to its excellent mechanical properties. Several studies have been conducted on PLA blends, with a focus on improving the brittleness of PLA to ensure its suitability for various applications. However, the increasing use of PLA has increased the contamination of PLA-based products in the environment because PLA remains intact even after three years at sea or in soil. This review focuses on analyzing studies that have worked on improving the degradation properties of PLA blends and studies how other additives affect degradation by considering different degradation media. Factors affecting the degradation properties, such as surface morphology, water uptake, and crystallinity of PLA blends, are highlighted. In natural, biotic, and abiotic media, water uptake plays a crucial role in determining biodegradation rates. Immiscible blends of PLA with other polymer matrices cause phase separation, increasing the water absorption. The susceptibility of PLA to hydrolytic and enzymatic degradation is high in the amorphous region because it can be easily penetrated by water. It is essential to study the morphology, water absorption, and structural properties of PLA blends to predict the biodegradation properties of PLA in the blends.