TY - JOUR
T1 - Well-mixed blends of HDPE and ultrahigh molecular weight polyethylene with major improvements in impact strength achieved via solid-state shear pulverization
AU - Diop, Mirian F.
AU - Burghardt, Wesley R.
AU - Torkelson, John M.
N1 - Funding Information:
We acknowledge support from a 3M Graduate Fellowship (to M.F.D.), the Initiative for Sustainability and Energy at Northwestern (ISEN), and Northwestern University . This study used Central Facilities supported by the MRSEC program of the National Science Foundation at the Northwestern University Materials Research Science and Engineering Center .
PY - 2014/9/15
Y1 - 2014/9/15
N2 - Compared with conventional polyolefins, ultrahigh molecular weight polyethylene (UHMWPE) possesses outstanding impact strength and crack resistance that make it desirable for a wide variety of applications. Unfortunately, UHMWPE has an ultrahigh viscosity that renders common, continuous melt-state processes ineffective for making UHMWPE products. Attempts to overcome this problem by blending UHMWPE with lower molecular weight high-density polyethylene (HDPE) by melt processing have typically led to poorly dispersed blends due to the vast viscosity mismatch between blend components. Here, we present solid-state shear pulverization (SSSP) as a mild, continuous, and simple approach for achieving effective and intimate mixing in UHMWPE/HDPE blends. These SSSP blends are easily processed by post-SSSP melt extrusion; for an SSSP blend with 50 wt% UHMWPE, we observe more than a factor of 1000 increase in viscosity at a shear rate of 0.01 s-1 but less than a factor of 5 increase at 100 s-1, the latter being more typical of melt-processing operations. Using extensional rheology, we confirm the strain hardening behavior of SSSP blends. Shear rheology and crystallization data show that the mixing between UHMWPE and HDPE can be improved with subsequent passes of SSSP and single-screw extrusion. Finally, we show that blending via SSSP leads to dramatic improvements in impact strength: as compared to literature results, injection-molded sample bars made from SSSP blends with 30-50 wt% UHMWPE exhibit very high values of notched Izod impact strength, 660-770 J/m (the impact strength of neat HDPE was 170 J/m).
AB - Compared with conventional polyolefins, ultrahigh molecular weight polyethylene (UHMWPE) possesses outstanding impact strength and crack resistance that make it desirable for a wide variety of applications. Unfortunately, UHMWPE has an ultrahigh viscosity that renders common, continuous melt-state processes ineffective for making UHMWPE products. Attempts to overcome this problem by blending UHMWPE with lower molecular weight high-density polyethylene (HDPE) by melt processing have typically led to poorly dispersed blends due to the vast viscosity mismatch between blend components. Here, we present solid-state shear pulverization (SSSP) as a mild, continuous, and simple approach for achieving effective and intimate mixing in UHMWPE/HDPE blends. These SSSP blends are easily processed by post-SSSP melt extrusion; for an SSSP blend with 50 wt% UHMWPE, we observe more than a factor of 1000 increase in viscosity at a shear rate of 0.01 s-1 but less than a factor of 5 increase at 100 s-1, the latter being more typical of melt-processing operations. Using extensional rheology, we confirm the strain hardening behavior of SSSP blends. Shear rheology and crystallization data show that the mixing between UHMWPE and HDPE can be improved with subsequent passes of SSSP and single-screw extrusion. Finally, we show that blending via SSSP leads to dramatic improvements in impact strength: as compared to literature results, injection-molded sample bars made from SSSP blends with 30-50 wt% UHMWPE exhibit very high values of notched Izod impact strength, 660-770 J/m (the impact strength of neat HDPE was 170 J/m).
KW - Blend
KW - High density polyethylene
KW - Ultrahigh molecular weight polyethylene
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U2 - 10.1016/j.polymer.2014.07.050
DO - 10.1016/j.polymer.2014.07.050
M3 - Article
AN - SCOPUS:84908147689
SN - 0032-3861
VL - 55
SP - 4948
EP - 4958
JO - Polymer
JF - Polymer
IS - 19
ER -