| Hard elastic material is a new type of elastomer gains much attention in recent years.Such materials have the resilience of the rubber, but the tensile modulus is higher than therubber. Because of its unique high resilience, good low temperature flexibility, high modulusand tensile pore-forming properties, access to wide attention and application. Microporousmembrane can be prepared by re-drawing hard elastic polypropylene (PP). The processing isthe key to the formation of materials’ hard elastic. The inorganic filler and nucleating agenthave significant modification on polypropylene, also effect on hard elastic and pore-formingof polypropylene cast film.This thesis study on the modification of PP by using inorganic filler and nucleating agent,the preparation of good hard elastic polypropylene film. The effects of hot-draw ratio,drawing rate, cooling rate, annealing were studied. We combine the modification andprocessing, investigated the influence on the structure and properties of PP microporousmembrane by re-drawing, inorganic filler and nucleating agent. The influence wascharacterized by DSC, SEM, universal testing machine, etc.The results showed that silica and kaolin can improve the strength and toughness of PP.Polypropylene grafted with maleic anhydride (MAPP) further improve the effect. Theaddition of silica and MAPP both are1phr, the composites compared with pure PP flexuralstrength and modulus were increased by20.6%and25.5%, respectively, impact strengthincreased by41.5%. SEM shows the notched impact fracture surface is rougher. The additionof silica and kaolin played the role of heterogeneous nucleation in polypropylene, promotedgrain refinement, increased crystallization temperature, and accelerated crystallization rate.Beta nucleating agent added in polypropylene could induced β crystalline, then increasing thecrystallization temperature and rate, effectively improve the toughness of PP. Using amidesnucleating agent0.1phr can make the impact strength increased three times. The rare earthnucleating agent have a better comprehensive modification effect, the optimum amount was0.2phr. Composites’ impact properties increased by1.9times, flexural properties increasedslightly.Using hot draw-controlled cooling rate-annealing treatment process for the preparation of hard elastic polypropylene film. The optimum processes were as follows:175℃heating30s, stretching400%at500mm/min,140℃heat treatment60minutes. Polypropylene hardelastic membrane has excellent overall performance: the tensile strength of64.2MPa, theelastic recovery percentage of88.5%. The properties of PP film are controlled by hot drawtemperature, tensile rate, cooling rate, annealing temperature and time. The higher tensile rate,the lower cooling rate, annealing time and temperature (80-140℃) to improve both help toimprove the material elastic recovery and tensile strength, but elongation at break declined.PP hard elastic film at room temperature cold drawing100%, then at120℃hot drawing200%, prepared microporous membranes have better comprehensive performance: manypores and uniform pore size, pore size of about50-100nm.By adding silica and kaolin, hard elastic PP film tensile strength increased, the elasticrecovery is slightly decreased and elongation at break decreased significantly. Stretch50%ofThe hard elastic membrane drawing50%at room temperature, then120℃hot drawing80%.The silica composite system can not form microporous, while kaolin composite system canform. There are smaller pore size and lower porosity compared to the pure PP system. Betanucleating agent added, the thermal stretching temperature of hard elastic film decreased, theelastic recovery also reduced. The higher beta crystal relative contents the greater to decline.Samples containing33%beta crystal at130℃heat treatment60mins after stretching, theelastic recovery percentage was85.9%. The membrane after re-drawing has uniform poredistribution, high porosity, and pore size of about50nm. The higher beta crystal contents theworse effect of pore forming. |
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