Reactive Compatibilization: Formation of Double-Grafted Copolymers by In Situ Binary Grafting and Their Compatibilization Effect

Enhanced Impact Resistance, Oxygen Barrier, and Thermal Dimensional Stability of Biaxially Processed Miscible Poly(Lactic Acid)/Poly(Butylene Succinate) Thin Films

This study investigates the crystallization, microstructure, and performance of poly(lactic acid)/poly(butylene succinate) (PLA/PBS) thin films processed through blown film extrusion and biaxial orientation (BO) at various blend ratios. Succinic anhydride (SA) was used to enhance interfacial adhesion in PLA-rich blends, while blends near 50/50 formed co-continuous phases without SA. Biaxial stretching and annealing, adjusted according to the crystallization behavior of PLA and PBS, significantly influenced crystallinity, crystallite size, and molecular orientation. Biaxial stretching induced crystallization and ordered chain alignment, particularly at the cold crystallization temperature (Tcc), leading to a 70-80-fold increase in impact resistance compared to blown films. Annealing further enhanced crystallinity, especially at the Tcc of PLA, resulting in larger crystallite sizes. BO films demonstrated reduced thermal shrinkage due to improved PLA crystalline structure, whereas PLA-rich blown films showed higher shrinkage due to PLA's lower thermal resistance. The SA-miscibilized phase reduced oxygen transmission in blown films, while BO films exhibited higher permeability due to anisotropic crystal orientation. However, the annealing of BO films, especially at high temperature (Tcc of PLA), further lowered oxygen permeability by promoting the crystallization of both PLA and PBS phases. Overall, the combination of SA compatibilization, biaxial stretching, and annealing resulted in substantial improvements in mechanical strength, dimensional stability, and oxygen barrier properties, highlighting the potential of these films for packaging applications.

Biodegradable reactive compatibilizers for efficient in-situ compatibilization of poly (lactic acid)/poly (butylene adipate-terephthalate) blends

The wide application of fully biodegradable polylactic acid/polybutylene terephthalate (PLA/PBAT) blends in environmentally friendly packaging were limited because of poor compatibility. Normal compatibilizers suffer from poor thermal stability and non-biodegradability. In this work, epoxy copolymer (MDOG) with different molecular structures were made of 2-methylene-1, 3-dioxoheptane, and glycidyl methacrylate as raw materials by free radical copolymerization. MDOG copolymers have good biodegradability and a high thermal decomposition temperature of 361 °C. The chemical reaction of the epoxy groups in MDOG with PLA and PBAT during the melting reaction improved the interfacial bonding by decreasing the particle size of PBAT. Compared to the PLA/PBAT blends, the tensile strength and fracture toughness of PLA/PBAT/MDOG blends were enhanced to 34.6 MPa and 115.8 MJ/m3, which are 25 % and 81 % higher, respectively. As a result, this work offers new methods for developing thermally stable and biodegradable compatibilizers, which will hopefully promote the development of packaging industry.

Strengthening Interfacial Adhesion and Foamability of Immiscible Polymer Blends via Rationally Designed Reactive Macromolecular Compatibilizers

Foams made of immiscible polymer blends have attracted great interest in both academia and industry, because of the integration of desirable properties of different polymers in a hybrid foam. However, the foamability and end-use properties are hampered because of the poor interfacial strength within the immiscible blends. Furthermore, few investigations have been carried out on the mechanisms by which interfacial strength and structure affect the foamability of polymer blends. In this work, two different reactive interfacial compatibilizers, i.e., poly(styrene-co-glycidyl methacrylate)-graft-poly(l-lactide) and poly(styrene-co-glycidyl methacry-late)-graft-poly(d-lactide), abbreviated as SG-g-PLLA and SG-g-PDLA, respectively, were designed and synthesized through reactive melt blending and subsequently applied to strengthen the interfacial strength and foamability of immiscible poly(butylene adipate-co-terephthalate) (PBAT)/poly(l-lactide) (PLLA) blends. Both compatibilizers could remarkably enhance the interfacial strength and foamability of the PBAT/PLLA blends, as evidenced by the significantly elongated dispersed phase in the resulting cocontinuous phase and more than 7000-fold increase in the cell density. Furthermore, the improved foamability was quantitively explained by the reduced gas diffusion and increased melt strength. Strikingly, the SG-g-PDLA introduced a stereocomplex crystal at the interface (i-SC), providing highly strengthened interfaces and nanoscale heterogeneous nucleation sites, which led to an energetically favorable cell nucleation. Moreover, foams with specifically laminated cell structures were fabricated by combining pressure-induced flow processing and i-SC strengthened interfaces. This work provides insight into the relationship between interfacial strength and formability of immiscible polymer blends and offers new possibilities for controlling cell morphologies and designing unique cell structures for polymer foams.

Improvement of PLLA Ductility by Blending with PVDF: Localization of Compatibilizers at Interface and Its Glycidyl Methacrylate Content Dependency

In this work, the localization of reactive compatibilizer (RC, containing poly(methyl methacrylate) (PMMA) backbone with randomly distributed glycidyl methacrylate (GMA) on it) at the polyvinylidene fluoride/poly(l-lactic acid) (PVDF/PLLA) interface has been manipulated by means of GMA contents. At the very beginning of mixing, RC tends to stay in the PVDF phase due to the miscibility between PVDF and PMMA. Upon further shearing, more and more PLLA chains have been grafted on PMMA backbone, producing PLLA-g-PMMA copolymer. The balanced stress on two sides accounts for the localization of compatibilizers at the PVDF/PLLA interface. Finally, the stress of the PLLA side has been enhanced remarkably due to the higher graft density of PLLA, resulting in the enrichment of the copolymer in the PLLA matrix. The migration of RC from the PVDF phase to the immiscible interface and PLLA matrix can be accelerated by employing RC with higher GMA content. Furthermore, the compatibilizer localization produces a significant influence on the morphology and ductility of the PVDF/PLLA blend. Only when the compatibilizers precisely localize at the interface, the blend exhibits the smallest domain and highest elongation at break. Our results are of great significance for not only the fabrication of PLLA with high ductility, but also the precise localization of compatibilizers at the interface of the immiscible blend.

Reactive Comb Polymer Compatibilized Immiscible PVDF/PLLA Blends: Effects of the Main Chain Structure of Compatibilizer

The compatibilizer with double comb structure has a superior compatibilizing effect for immiscible polymer blends due to the symmetrical structure on both sides of main chains. Extensive study related to the architectural effects of compatibilizer on the compatibilization has mainly focused on the side chains. We investigated the influence of the compatibilizer-main-chain structure on the compatibilizing effect for immiscible poly(vinylidene fluoride)/poly(L-lactic acid) (PVDF/PLLA) blends. Two reactive-comb compatibilizers with polystyrene (PS) and polymethylmethacrylate (PMMA) as main chains and PMMA as the side chains have been synthesized. PS is immiscible with both PLLA and PVDF, while PMMA is miscible with PVDF. It was found that both compatibilizers can improve the compatibility between the PLLA and PVDF, with different compatibilization effects. In the PVDF/PLLA (50/50) blends, 1 wt.% poly(styrene-co-glycidyl methacrylate)-graft-poly(methyl methacrylate) (RC-SG) tuned the morphology from the droplet-in-matrix structure to the co-continuous structure, while the blends with poly(methyl methacrylate-co-glycidyl methacrylate)-graft-poly(methyl methacrylate) (RC-MMG) kept the sea-island structure with even 3 wt.% loading. Moreover, RC-SG induces a wider co-continuous interval range than RC-MMG. The co-continuous structure obtained by RC-SG was also more stable than that by RC-MMG. It was further found that RC-SG-compatibilized PVDF/PLLA blends exhibit higher mechanical properties than the RC-MMG-compatibilized blends.

Super-tough poly (l-lactide) materials: Reactive blending with maleic anhydride grafted starch and poly (ethylene glycol) diacrylate

Super-tough poly (l-lactide) (PLLA) without compromising its biodegradability and biocompatibility was fabricated by reactive blending with PLLA and maleic anhydride grafted starch (MS)/poly (ethylene glycol) diacrylate (PEGDA). PEGDA as reactive compatibilizer exhibits higher compatibilization efficiency and significant plasticization effect in PLLA matrix. Fourier transform infrared spectroscopy (FT-IR) confirmed that PEGDA monomer successfully located at the molecules of MS and some interesterification reactions occurred between PEGDA and PLLA. The ductility of PLLA materials were significantly improved, for example, the elongation of break increased to 298% at the optimum PLLA/MS/PEGDA content. Dynamic mechanical thermal analysis (DMTA) demonstrated the glass transition temperature of blends decreased with the contents of MS/PEGDA increasing. The differential scanning calorimeter (DSC) results revealed that cold crystallization temperature and melting temperature of blends were decreased with the augment of the contents of MS/PEGDA. Wide angle X-ray diffraction (WARD) and DSC certified that a high crystalline article was obtained through practical extrusion process, which could propagate shear yielding deformation to dissipate energy during tensile fracture. Scanning electron microscope (SEM) demonstrated that the blends with PEGDA did not exhibit a visible phase-separated morphology from cryogenic fractured surfaces compared with the blend without PEGDA.