A novel long-chain branching (LCB) hydrogel, polyacrylamide grafted from poly(2-acrylamido-2-methylpropanesulfonic acid) via photo-induced polymerization, has been developed with excellent mechanical properties such as ultrahigh tensibility and high strength. Investigations of tensile and compressive properties indicate that the Young's modulus, ultimate strength and strain, toughness, compressive modulus and stress are significantly improved by introduction of LCB. Scanning electron microscopy (SEM) reveals that the amount of embedded micro-network structures in LCB gels is increased with an increase in the length of LCB. The compressive loading–unloading behaviour shows that the area of the hysteresis loop (the dissipated energy) for the first compressive cycle increases with the introduction of LCB and is higher than that for subsequent cycles. The energy dissipation mechanism is demonstrated for a better understanding of LCB gels. Furthermore, rheological measurements are also studied. Dynamic shear measurements show that both the storage modulus and the complex viscosity increase in the presence of LCB.
Yang Su,Tao Wang,Guodong Dang,Hongwei Zhou,Chunhai Chen
Polyether ether ketone (PEEK) mixed with manganese (Mn) of different valences was prepared to simulate conditions of impurity. The melt flow rate (MFR) and rheological behaviour were systematically studied to characterize the mobility from different angles. MFR test was used for the preliminary exploration of mixtures of Mn ions. The results showed that Mn, Mn(II), and Mn(IV) had little impact on the mobility of PEEK contrary to Mn(VII) and that long chain branching or cross-linking was suspected. Mn(VII) was determined to be the main object of this research. Capillary rheometer test demonstrated that the apparent shear viscosity constantly reduced with the increase of apparent shear rate, and that the addition of Mn(VII) could worsen the mobility of PEEK. Similarly, parallel plate rheometer studies proved that the complex viscosity increased along with the content of Mn(VII) and LCB was confirmed. Thermal analysis revealed that LCB occurred internally and that thermal stability was worse.
The main purpose of this work present a novel method for preparation of the polypropylene/polybutadiene/polyacrylamide (PP/PB/PAM) blends induced by pre-irradiation, the grafting reaction was conducted and completed before melting of the PP, and the formed grafted polymers served as the compatibilizer to enhance uniform dispersion in the melting stage subsequently. The EPR analysis manifests that there was peroxide on the PP powders after irradiation, which decomposed and induced grafting reaction when elevating temperature over 80 °C. The DSC and POM also demonstrated that the crystallization enhancement resulted from the heterogeneous nucleation attributed to both the grafted chains and their interactions. The hydrogen bonding interactions also assisted to construct the heterogeneous network structure in the melts appearing the nonlinear rheological behavior, and exhibited improved melt properties such as strain hardening and shear thinning like that of LCBPP's. Moreover, FTIR analysis confirms that H-bond interactions existed in the melts, their intensity and strength depend on both the PAM content and temperature. Having enhanced the melt strength and elasticity for the network structure in the melt, the PP/PB/PAM blends present well foaming performance especially in the sc-CO 2 with water process. The foams are obviously improved in the morphology and uniformity, and with much thinner cell walls, which originates from strengthening cell nucleation and plasticization after incorporation of the PAM. It is possible to tailor the linear polypropylene in a simple and practical way, which might broaden the field of possible applications and make light-weight PP a more competitive comparing to conventional used LCBPPs.
Le Yang,Yin Qin,Yang Li,Yinhan Xu,Yao Tao,Zhu Luo,Qiang Zheng
Long-chain branch (LCB) structures are critical for upgrading the poly(lactic acid) (PLA) melt performance. Polymer chains that are restructured by introducing LCBs via melt transesterification show higher reactive efficiencies and are environmentally friendly and gel free. Although PLA is environmentally friendly, its low melt strength hinders film blowing, blow molding, foaming, and other processes involving polymer melts. Therefore, the construction of LCBs is the key to solving this problem. However, because PLA easily thermally degrades, severe excessive transesterification-associated polymer degradation via the drastic chain-scission reaction substantially outcompetes the LCB-branching reaction, which substantially narrows the processing window for forming LCBs. Therefore, in this study, a dual hybrid branching (DHB) strategy was proposed to overcome these challenges. Specifically, surface-aminated ZnO (SAN-ZnO) nanoparticles were applied as an accelerant via ester activation by coordinating zinc atoms in ZnO with ester group oxygen atoms in PLA, which promoted transesterification between PLA and a trifunctional ester to form LCB–PLA. Moreover, amidogens on the SAN-ZnO surface could collect degraded PLA chains and react with their terminal carboxyl groups via amidation in situ to form DHB chains and thus restrain polymer overdegradation. Because DHB both facilitated LCB formation and restrained excessive polymer degradation, the PLA melt performance, especially the melt strength, was obviously improved to over 37 cN.
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