Effect Of Stress-Induced Reactions On Rheological Behavior And Properties Of Polymers

The effect of stress-induced reactions on rheological behavior and properties of some typically difficult processing polymers, mPE, UHMWPE, UHMWPE/HDPE blend and PVC, is studied in this paper through SEM, FT-IR, GPC, XRD, torque rheometer and high-pressure capillary rheometer analysis. The results show that during pan-milling, under the influence of the strong squeezing, shear and three-dimensional stress exerted by the pan-mill, the structure and morphology of these polymers are altered, the rheological behavior and properties of these difficult processing polymers get improved. The method is proved to be a viable, easy in operation, clean and efficient routes in polymer processing.1. After 10 cycles of pan-milling, the melt flow index of mPE is increased from 1.91g/10min to 3.28g/10min (230℃, 2.16kg), the critical shear rate from 1152s-1 to 2880s-1. Pan-milling can shorten melting time, lighten the load of processing machine and improve the surface quality of extrudate, the excellent impact property of mPE are remained after pan-milling, elongation at break, Young's modulus and strength at break of mPE are improved. After 15 cycles of pan-milling, the melt flow index of UHMWPE is increased from 0g/10min to 0.096g/10min (250℃, 21.6kg). Strength at yield and Young's modulus of UHMWPE are increased and elongation at break is unchanged, strength at break is slightly decreased.2. Addition of HDPE may improve the processing flowability of UHMWPE. The melt flow index of 10 cycles co-milled UHMWPE/HDPE (70/30) blend reaches 0.926g/10min, as much as 4 times of un-milled samples. This result makes it possible for UHMWPE to process in ordinary processing equipment. The solid-state stress induced by pan-mill is able to overcome the difficulty of viscosity un-matching between UHMWPE and HDPE melt. The mechanical properties get increased evidently. Compared with un-milled UHMWPE, strength at break, yield strength, Young's modulus and elongation at break of UHMWPE/HDPE (70/30) blend pan-milled 10 cycles increases from 30.4MPa, 24.16MPa, 765.8MPa, 505.8% to 41.0MPa, 25.4MPa, 1163MPa, 530.4% respectively, better than UHMWPE alone also.3. Through pan-milling, PVC's multilayers structure and microcrystal structure are destroyed, the molecular weight of PVC is decreased after pan-milling. The experimental results show the grain size of PVC S1000 reduces from 160μm to 3.3μm after 10 cycles of pan-milling, the plasticizing time and torque at balance drop down from 132s to 33s and from 22.1Nm to 18.6Nm respectively, both plasticizing rate and melting efficiency are improved, the surface quality of PVC extrudate gets advanced, die swell is decreased, both processabilities and mechanical properties of pan-milled PVC are improved. Strength at yield and Young's modulus of PVC S1000 increase from 58.5M and 2.36GPa to 66.2MPa and 2.94GPa respectively after 10 cycles of pan-milling.4. The Izod impact strength of PVC is 4.6kJ/m2. PVC-SBS copolymer is obtained through co-milling of PVC and SBS. After 10 cycles of pan-milling, the Izod impact strength of PVC/SBS (100/8) is enhanced from 22.4kJ/m2 to 72.4kJ/m2, strength at yield, elongation at break and Young's modulus are also improved in a certain extent. Co-milling may promote the dispersing ability of ultra-fine CaCO3 in the PVC matrix, reduce the agglomeration, the interfacial adhesion gets improved. The PVC/SBS/CaCO3 ternary blends are prepared through pan-milling. The impact strength of PVC/SBS/CaCO3 (100/8/4) blend pan-milled 10 cycles is 66.3 KJ/m2, strength at yield is 56.7 MPa, elongation at break is 92.9%, and Young's modulus is 2.39GPa, the toughness and stiffness of PVC blend are both improved.5. Through instantaneous high energy of laser, amorphous PVC is prepared. The absorbance spectrum of FTIR shows that the microcrystal of the laser-treated PVC is weakened and even disappeared. Changes in morphology of PVC particle, molecular weight and its distribution are indistinct, glass transition temperature of PVC is decreased. The plasticizing property is enhanced slightly.