Effect of wood flour as nucleating agent on the isothermal crystallization of poly(lactic acid)

The effect of wood flour (WF) as an efficient nucleating agent on the isothermal melt crystallization and isothermal cold crystallization behavior of poly(lactic acid) (PLA) was investigated by differential scanning calorimeter and polarized optical microscopy. It was found that the incorporation of 4 wt% WF promoted the crystallization of PLA about 4.2%. Polarized optical microscopy results showed the Maltese cross of the samples. The presence of the 4 wt% WF may increase the nucleation density, leading to the increase of the spherulites; however, the size of the spherulites decreased, and the structure became incomplete. The Avrami model was applied to analyze the isothermal crystallization kinetics. It is concluded that the addition of WF modified the crystallization process of PLA (the value of Avrami exponent changed). Various parameters, such as the crystallization half time and crystallization rate constant, reflect that 4 wt% WF significantly improves the crystallization process. The observations in this article indicate that WF is an efficient nucleating agent of PLA. Copyright © 2016 John Wiley & Sons, Ltd.     

Study on the multiple cyclization reactions and the formed structures in poly(acrylonitrile‐co‐itaconic acid) copolymers during thermal treatment

The present work provided some in‐depth understanding on the role of itaconic acid (IA) in the structural evolution of poly(acrylonitrile‐co‐itaconic acid) (PAI) polymers and the formed cyclic structures during thermal treatment. As the increasing content of IA, the cyclization initiated by the ionic mechanism increased with the less β‐amino nitrile formed and the higher extent of cyclization. The IA comonomer initiated multiple cyclization reactions, namely, the first ionic cyclization and the second ionic cyclization, by the jump transportation of activation species between different PAI chains during thermal treatment. The times of the jump transportation of activation species was about two or three at 250°C. The presence of IA comonomer promoted the formation of long sequence cyclic structures rather than isolated cyclic structure under non‐oxidative condition. The thermal stability of PAI was improved by the more and better cyclic structures and the crosslinking structures caused by the jump transportation of activation species, which reasonably resulted in a better graphitic lattice during the carbonization. Copyright © 2017 John Wiley & Sons, Ltd.     

Synergistic Effect of Polycarbonate on Reactive Core-Shell Particles Toughened Poly(Butylene Terephthalate)

Glycidyl methacrylate functionalized methyl methacrylate-butadiene-styrene copolymer (MBS-g-GMA) core-shell particles were prepared via an emulsion polymerization process. MBS-g-GMA was used to toughen poly(butylene terephthalate) (PBT) and the synergistic toughening effect of polycarbonate (PC) on PBT/MBS-g-GMA blends were investigated. Notched impact tests showed the percolation threshold became lower with the increase of PC content. Transmission electron microscopy displayed a very good dispersion of MBS-g-GMA particles in the PBT matrix with the different PC contents. The synergistic toughening effect was due to the encapsulation structure of PC which could facilitate the whole PBT matrix to yield. The more perfect the encapsulation structure formed, the more obvious the synergistic toughening the PC achieved. Sufficient strength of the phase interface was important to ensure the stress transfer effectively and facilitate the whole PBT matrix to yield. The interface strength between PC and MBS-g-GMA could be ensured by the good miscibility between Poly(methyl methacrylate) (PMMA) (grafted onto the polybutadiene-based rubber core) and PC. For the PBT/PC, the transesterification between PBT and PC improved the interface strength of the PBT and PC phases, as demonstrated by Fourier transform infrared spectroscopy (FTIR) scans. Scanning electron microscopy results showed shear yielding of the matrix and cavitation of the rubber particles were the major toughening mechanisms.     

Enhancing the thermal stability of poly(methyl methacrylate) by removing the chains with weak links in a continuous polymerization

A novel method is proposed to produce PMMA with excellent thermal stability by a continuous process composed of polymerization and devolatilization steps. It is based on the fact that free radical polymerized PMMA is a mixture of polymer chains with different structure, a small fraction of which, containing head-to-head linkages or unsaturated ends, is less thermally stable and the major portion without those defect structures which is much more stable. Our idea is selectively remove the unstable chains from this mixture by pre-decomposing them at suitable temperatures in a continuous process, leaving the stable portion as the final PMMA product. The results showed that during the continuous process, the chains with head-to-head linkages were eliminated by conducting the polymerization at 155 °C, and then the chains with unsaturated ends were removed by devolatilization at 300 °C. The final PMMA was thermally stable up to 313 °C.     

SAN共聚物组成对PVC/ABS共混物相容性的影响

采用乳液聚合技术通过改变共聚单体的投料比(St/AN)合成了一系列不同AN结合量的ABS接枝共聚物粉料和SAN共聚物.将其与聚氯乙烯(PVC)和邻苯二甲酸二辛酯(DOP)熔融共混分别制得了PVC/ABS、PVC/SAN、PVC/ABS/DOP和PVC/SAN/DOP共混物,利用SEM、TEM和动态力学粘弹谱仪(DMA)对共混物的相容性和相结构进行了表征.结果发现,在PVC/ABS共混体系中,尽管改变接枝SAN共聚物的AN结合量,PVC和SAN共聚物均为不相容体系;在该共混物中引入增塑剂DOP后,虽然当SAN共聚物AN结合量小于23.4 wt%时,共混物在室温以上只存在一个tanδ峰,但形态结构研究结果表明共混物仍为不相容体系,共混物的相区尺寸明显地依赖于SAN共聚物中的AN结合量,当AN结合量为23.4 wt%时相区尺寸最小.     

L-tyrosine-assisted synthesis of nanosilver/titanium nitride with hollow microsphere structure for electrochemical detection of hydrogen peroxide

Journal of Solid State Electrochemistry - The nano-Ag–TiO2 hollow microsphere precursors were prepared by the one-pot solvothermal method using L-tyrosine as the template agent and reducing...