Mechanical fracture behavior of polyacetal and thermoplastic polyurethane elastomer toughened polyacetal

Abstract

Polyacetal (POM) toughening with thermoplastic polyurethane (TPU) elastomer was investigated in terms of Theological, mechanical, and morphological properties. Polyacetal can be effectively toughened by the blending with TPU elastomer and the improvement on toughness is found most significant with TPU content from 20 to 30 percent. POM does fracture in ductile mode under extremely low deformation rate and the ductile‐brittle transition rate is at 0.5 mm/min. The transition rate is increased with the increase of elastomer content. The precrack hysteresis energy is important in dictating the failure mode. The experimental results show the hysteresis energy (under constant load) increases with the increase of elastomer content and the decrease of deformation rate. Greater hysteresis energy results in larger precrack plastic zone size and thus tends to shift the fracture mode from brittle to ductile as the critical size of the plastic zone is reached. The adoption of the slow rate fracture method has the advantages of ranking toughness of very brittle polymeric materials vs. the conventional Izod or Charpy impact method by varying temperatures. FTIR shows significant interaction between POM and TPU which is probably responsible for the TPU elastomer being such an efficient toughening agent for POM. Delamination in the buffer zone between the plane‐strain and the plane‐stress is discovered and the possible mechanism is discussed.

The influence of molecular weight on the properties of polyacetal/hydroxyapatite nanocomposites. Part 1. Microstructural analysis and phase transition studies

“…POM samples prepared by cooling from the melt exhibits the ECC bands more clearly, allowing to speculate that the POM sample crystallized from the melt is a mixture of ECC and FCC in a complicated manner. It was assumed that lamellar stacking structure formed in the temperature region I (primary crystallization) becomes tighter in the temperature region II (secondary crystallization) by a generation of second lamellae in between the original lamellae [30,31].…”

Interfacial reaction and its influence on phase morphology and impact properties of modified‐polyacetal/thermoplastic polyurethane blends

“…Several researchers [1][2][3][4][5][6][7][8][9][10][11][12][13] investigated the toughened POM/TPU blends focusing on physical properties, fracture behavior, and toughening mechanism. It was reported that the toughness of the POM/TPU blends depend on the concentration of TPU, [2][3][4]6,8,9,11 the interparticle distance of dispersed TPU phase 10,13 and the compatibility between POM and TPU. 12,13 With reagard to compatibilizers for the POM/TPU blends, Mehrabzadeh et al reported that 3% of diphenylmethane diisocyanate (MDI) in the POM/TPU (85/15 by weight) blend reduced the particle size of TPU and achieved the maximum impact strength, 12 and Gao et al reported that polystyrene-block-poly(ethylene-butylene)-block-polystyrene grafted with maleic anhydride (SEBS-graft-MA) enhanced the interfacial interaction between POM and TPU.…”

Stress relaxation behavior of polyacetal–thermoplastic polyurethane elastomer blends

“…The blend AU73 exhibits a 150% increment in impact strength, and this observation is in consonance with that of Chang et a1. 12 who have made studies with POM blends containing up to 30% TPU. It appears that addition of TPU exceeding 30% TPU does not improve the impact strength but decreases it.…”