Standard methods for characterizations of structure and hydrolytic degradation of aliphatic/aromatic copolyesters

Characterization Techniques of Polymer Aging: From Beginning to End

Polymers have been widely applied in various fields in the daily routines and the manufacturing. Despite the awareness of the aggressive and inevitable aging for the polymers, it still remains a challenge to choose an appropriate characterization strategy for evaluating the aging behaviors. The difficulties lie in the fact that the polymer features from the different aging stages require different characterization methods. In this review, we present an overview of the characterization strategies preferable for the initial, accelerated, and late stages during polymer aging. The optimum strategies have been discussed to characterize the generation of radicals, variation of functional groups, substantial chain scission, formation of low-molecular products, and deterioration in the polymers' macro-performances. In view of the advantages and the limitations of these characterization techniques, their utilization in a strategic approach is considered. In addition, we highlight the structure-property relationship for the aged polymers and provide available guidance for lifetime prediction. This review could allow the readers to be knowledgeable of the features for the polymers in the different aging stages and provide access to choose the optimum characterization techniques. We believe that this review will attract the communities dedicated to materials science and chemistry.

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.

Chemical upcycling of polylactide (PLA) and its use in fabricating PLA-based super-hydrophobic and oleophilic electrospun nanofibers for oil absorption and oil/water separation

Circular design and fabrication of PLA nanofiber filters from PLA wastes for effective oil decontamination and oil/water separation.

Catalytic developments in the epoxidation of vegetable oils and the analysis methods of epoxidized products

Functionalization of vegetable oils (VOs) including edible, non-edible, and waste cooking oil (WCOs) to epoxides (EVOs) is receiving great attention by many researchers from academia and industry because they are renewable, versatile, sustainable, non-toxic, and eco-friendly, and they can partially or totally replace harmful phthalate plasticizers. The epoxidation of VOs on an industrial scale has already been developed by the homogeneous catalytic system using peracids. Due to the drawbacks of this method, other systems including acidic ion exchange resins, polyoxometalates, and enzymes are becoming alternative catalysts for the epoxidation reaction. We have reviewed all these catalytic systems including their benefits and drawbacks, reaction mechanisms, intensification of each system in different ways as well as the physicochemical properties of VOs and EVOs and new findings in recent years. Finally, the current methods including titrimetric methods as well as ATR-FTIR and 1H NMR for determination of conversion, epoxidation, and selectivity of epoxidized vegetable oils (EVOs) are also briefly described.