Plasticization mechanism of biobased plasticizers comprising polyethylene glycol diglycidyl ether-butyl citrate with both long and short chains on poly(lactic acid).

Polylactic acid (PLA), a biodegradable polymer with low flexibility, is commonly plasticized with small molecules like tributyl citrate (TBC) for film production. However, these plasticizers, which lack chemical bonds or strong intermolecular interactions with the matrix, tend to migrate to the film surface over time. Their inclusion often compromises material strength for flexibility, increasing elongation at break but reducing tensile strength. In this research, by combining citric acid with n-butanol (B) and poly(ethylene glycol) diglycidyl ether (E), we synthesized three plasticizers, namely TE3, TE2B1, and TE1B2, to enhance the flexibility of PLA. TE2B1 and TE1B2 are equipped with butyl ester groups that offer effective plasticizing effects. Additionally, the incorporation of long-chain alkyl featuring epoxy groups can boost the interaction with PLA. The results showed that the epoxy groups of the long-chain alkyl plasticizers can improve the elongation at break without compromising tensile strength significantly. The migration of plasticizer from PLA matrix can be reduced by strong interactions like chemical bonds, entanglements, and hydrogen bonding with PLA. TE1B2 demonstrated the best plasticizing effect. Adding 15 portions of TE1B2 and TBC separately increased PLA's elongation at break to 304 % and 242 %, with tensile strengths of 36.1 MPa and 22.3 MPa, respectively.

Epoxidized Soybean Oil Toughened Poly(lactic acid)/Lignin-g-Poly(lauryl methacrylate) Bio-Composite Films with Potential Food Packaging Application.

The application of lignin as a filler for poly (lactic acid) (PLA) is limited by their poor interfacial adhesion. To address this challenge, lignin-graft-poly(lauryl methacrylate) (LG-g-PLMA) was first blended with poly (lactic acid), and then epoxidized soybean oil (ESO) was also added to prepare PLA/LG-g-PLMA/ESO composite, which was subsequently hot pressed to prepare the composite films. The effect of ESO as a plasticizer on the thermal, mechanical, and rheological properties, as well as the fracture surface morphology of the PLA/LG-g-PLMA composite films, were investigated. It was found that the compatibility and toughness of the composites were improved by the addition of ESO. The elongation at break of the composites with an ESO content of 5 phr was increased from 5.6% to 104.6%, and the tensile toughness was increased from 4.1 MJ/m3 to 44.7 MJ/m3, as compared with the PLA/LG-g-PLMA composite without ESO addition. The toughening effect of ESO on composites is generally attributed to the plasticization effect of ESO, and the interaction between the epoxy groups of ESO and the terminal carboxyl groups of PLA. Furthermore, PLA/LG-g-PLMA/ESO composite films exhibited excellent UV barrier properties and an overall migration value below the permitted limit (10 mg/dm2), indicating that the thus-prepared biocomposite films might potentially be applied to environmentally friendly food packaging.

Bio-based epoxidized soybean oil branched cardanol ethers as compatibilizers of polybutylene succinate (PBS)/polyglycolic acid (PGA) blends.

Blending poly(butylene succinate) (PBS) with another biodegradable polymer, polyglycolic acid (PGA), has been demonstrated to improve the barrier performance of PBS. However, blending these two polymers poses a challenge because of their incompatibility and large difference of their melting temperatures. In this study, we synthesized epoxidized soybean oil branched cardanol ether (ESOn-ECD), a bio-based and environmentally friendly compatibilizer, and used it to enhance the compatibility of PBS/PGA blends. It was demonstrated that the terminal carboxyl/hydroxyl groups of PBS and PGA can react with ESOn-ECD in situ, leading to branching and chain extension of PBS and PGA. The addition of ESO3-ECD to the blend considerably diminished the dispersed phase of PGA. Specifically, in comparison to the PBS/PGA blend without a compatibilizer, the diameter of the PGA phase decreased from 2.04 µm to 0.45 µm after the addition of 0.7 phr of ESO3-ECD, and the boundary between the two phases became difficult to distinguish. Additionally, the mechanical properties of the blends were improved after addition of ESO3-ECD. This research expands the potential applications of these materials and promotes the use of bio-based components in blend formulations.

Development of PLA/Lignin Bio-Composites Compatibilized by Ethylene Glycol Diglycidyl Ether and Poly (ethylene glycol) Diglycidyl Ether.

Poly (lactic acid) (PLA) is a promising green substitute for conventional petroleum-based plastics in a variety of applications. However, the wide application of PLA is still limited by its disadvantages, such as slow crystallization rate, inadequate gas barrier, thermal degradation, etc. In this study, lignin (1, 3, 5 PHR) was incorporated into PLA to improve the thermal, mechanical, and barrier properties of PLA. Two low-viscosity epoxy resins, ethylene glycol diglycidyl ether (EGDE) and poly (ethylene glycol) diglycidyl ether (PEGDE), were used as compatibilizers to enhance the performance of the composites. The addition of lignin improved the onset degradation temperature of PLA by up to 15 °C, increased PLA crystallinity, improved PLA tensile strength by approximately 15%, and improved PLA oxygen barrier by up to 58.3%. The addition of EGDE and PEGDE both decreased the glass transition, crystallization, and melting temperatures of the PLA/lignin composites, suggesting their compatabilizing and plasticizing effects, which contributed to improved oxygen barrier properties of the PLA/lignin composites. The developed PLA/lignin composites with improved thermal, mechanical, and gas barrier properties can potentially be used for green packaging applications.

Design of Novel PLA/OMMT Films with Improved Gas Barrier and Mechanical Properties by Intercalating OMMT Interlayer with High Gas Barrier Polymers.

Polymer/clay composites are an innovative class of materials. In this study, we present a facile method for the preparation of biodegradable and robust PLA/organomodified montmorillonite (OMMT) composite films with excellent gas barrier performance. When the design of PLA/OMMT composite films, in addition to making OMMT have good intercalation effect in the matrix, the compatibility of intercalating polymer and matrix should also be considered. In this work, two polymers with high gas barrier properties, namely poly(vinyl alcohol) (PVA) and ethylene vinyl alcohol copolymer (EVOH), were selected to intercalate OMMT. The morphology and microstructures of the prepared PLA/PVA/OMMT and PLA/EVOH/OMMT composites were characterized by the X-ray diffraction measurement, scanning electron microscopy, and differential scanning calorimetry. It was shown that the good dispersibility of PVA in the PLA matrix, rather than the intercalation effect, was responsible for the improved gas barrier and mechanical properties of PLA/PVA/OMMT composite. The elongation at break increases from 4.5% to 22.7% when 1 wt % PVA is added to PLA/OMMT. Moreover, gas barrier of PLA/PVA1/OMMT measured as O2 permeability is 52.8% higher than that of neat PLA. This work provides a route to intercalate OMMT interlayer with high gas barrier polymers and thus can be a useful reference to fabricate PLA/OMMT composites with improved gas barrier and mechanical properties. A comparison of oxygen permeabilities with existing commercial packaging films indicates that the biodegradable PLA/PVA/OMMT may serve as a viable substitute for packaging film applications.

Improvement of the Gas Barrier Properties of PLA/OMMT Films by Regulating the Interlayer Spacing of OMMT and the Crystallinity of PLA.

A high gas barrier performance should be ensured in case of biodegradable packing applications. However, the gas barrier properties of the biodegradable poly(lactic acid) (PLA) are not much effective. Nanocomposites can provide innovative solutions to enhance the barrier performance. In this study, different weight percentages of organically modified montmorillonite (OMMT) (0, 2, 4, 6, 8, and 10 wt %)-incorporated PLA/OMMT nanocomposites were prepared by melt mixing. Ethylene glycol diglycidyl ether (EGDE) was used to regulate the interlayer spacing of OMMT and increase the PLA crystallinity to further improve the gas barrier performance of the PLA/OMMT films. The crystallinity of PLA was significantly improved because EGDE-modified OMMT served as an efficient nucleating agent. The PLA/EGDE/OMMT films demonstrated a unique structure such that the adjacent OMMT layers were linked through the PLA crystals that serve as a bridge with respect to the spaces between the OMMT layers. The O2 permeability of the PLA/EGDE4/OMMT-6 film decreased by approximately 79% when compared with that of the neat PLA film. X-ray diffraction and differential scanning calorimetry analyses denoted that the reduced oxygen permeability of the PLA/EGDE4/OMMT-6 film can be primarily attributed to the high crystallinity of the PLA matrix and the bridging effect of the PLA crystals between two adjacent layers. Based on the experimental results, the relation between the relative permeability and vol % OMMT is in good agreement with that of the predicted values obtained using the Bharadwaj model when S = 0. The added EGDE weakened the thermal stability and tensile strength, mainly because of degradation of the hydroxyl groups of EGDE formed by epoxy ring opening, and these hydroxyl groups can promote PLA matrix degradation. However, the practical application temperature of the packaging film is considerably lower than the thermal decomposition temperature; therefore, the reduction of the thermal decomposition temperature does not affect the use of the packaging film.

Enhancement of Gas Barrier Properties of Graphene Oxide/Poly (Lactic Acid) Films Using a Solvent-free Method.

Graphene oxide(GO)/polylactic acid (PLA) nanocomposite, prepared using a solvent-free melt mixing processing, is investigated as a potential oxygen barrier packaging film in this work. In order to disperse GO homogeneously in PLA matrix, hydrophobic silane coupling agent, i.e., γ-(2,3-epoxypropoxy)propyltrimethoxysilane (KH560), is used to modify the graphene oxide sheets. The modified GO is able to be well bonded to the PLA due to the formation of covalent bonds between the epoxy groups of KH560 and the carboxyl and hydroxyl terminal groups of PLA. Furthermore, the thermal stability of GO is enhanced due to the long alkyl side chain of KH560, which could also increase the crystallinity of PLA. As a result, the crystallinity of PLA is significantly improved because of the linear KH560 chains, which can act as nucleating agents to improve the crystallization. The KH560-GO helps to reduce the O2 permeability of KH560-GO/PLA composite films via a dual-action mechanism: (1) providing physical barrier due to their native barrier properties, and (2) by resulting in higher degree of crystallinity. The as-prepared KH560-GO0.75/PLA is able to exhibit ca. 33% and ca. 13% decrease in the PO2 than the neat PLA and GO0.75/PLA film, respectively. Finally, the mechanical properties and impact fractured surfaces indicate that the increase in the tensile strength and elongation at break value of KH560-GO/PLA are due to the strong interfacial adhesion and the strong bonding between the epoxy group of KH560-GO and hydroxyl and carboxyl acid terminal groups of PLA matrix.

Robust and nanoparticle-free superhydrophobic cotton fabric fabricated from all biological resources for oil/water separation.

Traditional superhydrophobic cotton fabrics (SCFs) for oil/water separation were usually fabricated by surface coating with inorganic nanoparticles combined with nonrenewable and nonbiodegradable or even toxic fossil-based chemicals, which would lead to secondary environmental pollution after their lifetime. In this study, we report robust, nanoparticle-free, fluorine-free SFC, which was prepared by acid etching followed by surface coating with epoxidized soybean oil resin (CESO) and subsequent modification with stearic acid (STA). No toxic compound and no nanoparticle were included within the SCF and all the raw materials including cotton fabric, CESO and STA are biodegradable and derived from biological resources. The SCF showed excellent mechanical stability and chemical/environmental resistances. The superhydrophobicity of the SFC survived from mechanical abrasion, tape peeling, ultrasonication, solvent erosion and low/high temperature exposure. The SCF also exhibited good acid/alkali resistance with contact angle over 150° toward different pH water droplets. Moreover, the SCF could efficiently separate oil/water mixtures with efficiency above 97.9% and the superhydrophobicity remained after reusing for at least 10 times. The fully biological-derived SCF with excellent mechanical and chemical resistances exhibit great potential for separation of oil/water mixtures.

Influence of ether linkage on the enzymatic degradation of PBS copolymers: Comparative study on poly (butylene succinate-co-diethylene glycol succinate) and poly (butylene succinate-co-butylene diglycolic acid).

The difference of enzymatic degradation behavior between Poly (butylene succinate-co-diethylene glycol succinate) (PBS-co-DEGS) and Poly (butylene succinate-co-butylene diglycolic acid) (PBS-co-BDGA) was studied in a Tetrahydrofuran (THF)/toluene mixed system by Novozym 435 (N435, immobilized Candida Antarctica lipase supported on acrylic resin) catalysis for 30 h. These two copolymers (modified with alcoholic acid by ether linkage) were synthesized by melt polycondensation and characterized by 1H NMR. The average molecular weight and thermal property before and after degradation were determined by gel permeation chromatography (GPC) and thermogravimetric analysis (TGA), respectively. Results revealed that end-chain degradation of DEG20 (20% content diethylene glycol of diols) and intramolecular random degradation of DGA20 (20% content diglycolic acid of diacids) both occurred at the same time from 0 h to 12 h. TGA curves show that after degradation by N435, the T-5% of both copolymers decreased from about 300 °C to below 210 °C. In degradation products (linear and cyclic oligomers, no monomer was appeared below 10 degree of polymerization. According to the molecular docking results, the free binding energy between PC lipase and substrate was in the order of BDGAB < DEGSDEG < BSDEG < BSB. Thus, the enzymatic degradability of PBS-co-DEGS is more effective than that of PBS-co-BDGA.