“半稀溶液”中超高分子量聚乙烯链缠绕结构的演变行为

Emergence of Chain Entanglement of UHMWPE in“Semi-Dilute Solution”

通过熔融共混法制备超高分子量聚乙烯/线性低密度聚乙烯(UHMWPE/LLDPE)和超高分子量聚乙烯/聚乙烯蜡(UHMWPE/PE-wax)共混物,以振荡剪切流变测试和脆断截面SEM研究不同浓度UHMWPE对共混物流变行为和材料微观形貌变化的影响,尤其是UHMWPE在共混物中达到一定浓度开始形成缠结结构时的行为变化。UHMWPE/LLDPE共混物在流变测试中相容性良好,当UHMWPE浓度大于0.84%(wt),即临界交叠浓度(孤立高分子线团逐渐靠近开始成为线团密堆积时的浓度)的4倍,频率扫描曲线在低频区显示为与频率无关的类固态凝胶行为,网络结构开始形成;时间扫描曲线表明UHMWPE的浓度在大于0.84%(wt)时储能模量逐渐增大,UHMWPE的缠结有所体现。采用分子量低于缠结分子量Me的聚乙烯蜡为基体,UHMWPE/PE-wax共混物的时间扫描在浓度0.84%(wt)(临界交叠浓度的4倍)时储能模量增加明显。通过SEM观察UHMWPE/PE-wax共混物脆断面,发现该浓度下开始出现丝状物结构,表明了缠结和网络结构的形成。

Ultra-high molecular weight polyethylene （UHMWPE）, linear low density polyethylene （LLDPE） and polyethylene wax （PE-wax） were used to prepare UHMWPE/LLDPE and UHMWPE/PE-wax blends with relatively low UHMWPE concentrations. The influence of different concentrations of UHMWPE on the formed structure of UHMWPE chain entanglement in two blends, especially the critical concentration of onset of entanglement, was investigated by applying small oscillatory shear rheology and scanning electron microscope. The compatibility of UHMWPE/LLDPE blends was good according to rheologieaI tests. It is suggested that when the concentration of UHMWPE in UHMWPE/LLDPE blends is higher than 1.68% （wt）, the blends perform as solid gel independent of frequency at region of low frequency in frequency sweep curves, at the same time, the storage modulus begins to increase in time sweep curves. And with PE wax as a lower molecular weight matrix, the storage modulus of UHMWPE/PE-wax blends increase significantly, when the concentration of UHMWPE in UHMWPE/PE-wax blends is higher than 0.84% （wt）. Furthermore, the emergence of filaments in images of brittle fracture surface of UHMWPE/PE-wax blends coincidently begins at the concentration of 0. 84% （wt）. In conclusion, UHMWPE forms entanglement structure in the blends with UHMWPE concentrations above a critical value of c=0. 84% （wt）, four times the critical overlap concentration.