Solid state features and mechanical properties of PEI/PBT blends

Crystallization and Performance of Polyamide Blends Comprising Polyamide 4, Polyamide 6, and Their Copolymers

Polyamide 4 (PA4) is a biobased and biodegradable polyamide. The high hydrogen bond density of PA4 bestows it with a high melting point that is close to its thermal decomposition temperature, thereby limiting the melt processing of PA4. In this study, PA4 was blended with polyamide 6 (PA6) and further modified with copolyamide 4/6 (R46). The effects of composition on the crystallization behavior of the blends were studied. The results demonstrated that the binary PA4/PA6 (B46) and ternary PA4/PA6/R46 (B46/R46) blends formed two crystalline phases (PA4- and PA6-rich phases) through crystallization-induced phase separation. With increasing PA6 content, the thermal stability and crystallinity of the B46 blend increased and decreased, respectively, and the contribution of PA6 toward the crystallization of the PA4-rich phase diminished. Molecular dynamics simulations showed the molecular chain orientation of the B46 blends well. The melting points, crystallinities, and grain sizes of the B46/R46 blends were lower than those of the B46 blends. The crystallization of the PA4-rich phase was restrained by the dilution effect of molten-state PA6, and the nucleation and crystallization of the PA6-rich phase were promoted by the presence of crystallized PA4. The B46 blends with 30-40 wt% PA6 had the best mechanical properties.

Acid-triggered, degradable and high strength-toughness copolyesters: Comprehensive experimental and theoretical study

The popularization and widespread use of degradable polymers is hindered by their poor mechanical properties. It is of great importance to find a balance between degradation and mechanical properties. Herein, poly(butylene terephthalate) (PBT) modified by SPG diol from 10% to 40 mol% were synthesized through a two-step polycondensation reaction. Chemical structures, thermal properties, mechanical properties, viscoelastic behavior and degradation of poly(butylene terephthalate-co-spirocyclic terephthalate) (PBST) were investigated. The SPG could toughen the copolyesters and the elongation at break of PBST20 was up to 260%. Moreover, the introduction of SPG enables to provide an acid-triggered degradable unit in the main chain. PBSTs copolymers maintain stable structures in a neutral environment, and the degradation under acid conditions will be unlocked. As tailoring the content of SPG, the degradation rate of the chain scission in response to acid stimuli will be adjusted. The acid degradation was proved to be occurred at the SPG units in the amorphous phase by DSC, XRD, GPC and ¹H NMR tests. After the acid degradation, the hydrolysis rate will also be accelerated, adapting to the requirements of different degradation schedules. The plausible hydrolytic pathways and mechanisms were proposed based on Fukui function analysis and density functional theory (DFT) calculation.

Structure and Properties of Reactively Extruded Opaque Post-Consumer Recycled PET

The recyclability of opaque PET, which contains TiO₂ nanoparticles, has not been as well-studied as that of transparent PET. The objective of this work is to recycle post-consumer opaque PET through reactive extrusion with Joncryl. The effect of the reactive extrusion process on the molecular structure and on the thermal/mechanical/rheological properties of recycling post-consumer opaque PET (r-PET) has been analyzed. A 1% w/w Joncryl addition caused a moderate increase in the molecular weight. A moderate increase in chain length could not explain a decrease in the overall crystallization rate. This result is probably due to the presence of branches interrupting the crystallizable sequences in reactive extruded r-PET (REX-r-PET). A rheological investigation performed by SAOS/LAOS/elongational studies detected important structural modifications in REX-r-PET with respect to linear r-PET or a reference virgin PET. REX-r-PET is characterized by a slow relaxation process with enlarged elastic behaviors that are characteristic of a long-chain branched material. The mechanical properties of REX-r-PET increased because of the addition of the chain extender without a significant loss of elongation at the break. The reactive extrusion process is a suitable way to recycle opaque PET into a material with enhanced rheological properties (thanks to the production of a chain extension and long-chain branches) with mechanical properties that are comparable to those of a typical virgin PET sample.

Tuning the compatibility to achieve toughened biobased poly(lactic acid)/poly(butylene terephthalate) blends

A series of sustainable biobased polymer blends from poly(lactic acid) (PLA) and poly(butylene terephthalate) (PBT) were fabricated and characterized. These blends are engineered to achieve optimal mechanical properties and toughness with a reactive epoxidized styrene-acrylic copolymer (ESAC) compatibilizer, and an ethylene-n-butyl-acrylate-co-glycidyl methacrylate (EBA-GMA) elastomer-based compatibilizer. The results showed that the tensile strength, modulus, flexural strength and modulus of the PBT increase, while the elongation at break and notched impact strength decrease after blending with the biopolymer PLA. The full co-continuity of PLA in PBT was confirmed at a 50/50 wt% blend ratio. The droplet size of the PLA was reduced and the distinct phases of the blends were gradually diminished with the increasing content of the ESAC compatibilizer. The increase in the complex viscosity of the blends was due to the formation of PLA-g-PBT copolymers in the blend after addition of reactive compatibilizers. The incorporation of both compatibilizers in the blends led to superior notched impact strength in comparison to only a single compatibilizer used in the blends. The synergistic effect of both compatibilizers effectively reduces the PLA droplet size and improves the dispersion of PLA in PBT as evidenced by atomic force microscopy (AFM) topography observations. The high toughness of the blends corresponds to the formation of effective EBA-GMA structures and enhanced interfacial compatibilization due to the synergistic effect of the compatibilizers.

Novel toughened biobased polymer blends from poly(lactic acid) and poly(butylene terephthalate) were developed by judicious compatibilization.

Morphology, mechanical and dielectric properties, and rheological behavior of EAGMA toughened microcellular PEI–EAGMA foam

EAGMA plays an important role in the microcellular structure formation and had an excellent toughening effect on the PEI–EAGMA system.