Effect of a cross-linking agent on the foamability of microcellular injection molded thermoplastic polyurethane

Abstract

Thermoplastic polyurethane is one of the most versatile thermoplastic materials being used in a myriad of industrial and commercial applications. Thermoplastic polyurethane foams are finding new applications in various industries including furniture, automotive, sportswear, and packaging because of their easy processability and desirable, customizable properties. Low bulk density and a good foam microstructure are important properties that affect the mechanical properties, economics, and performance of the final product. In this study, the effect of a cross-linking agent on the foamability of microcellular injection molded thermoplastic polyurethane was studied with an aim to reduce the bulk density while achieving a consistent microstructure. Gel permeation chromatography showed an increase in the weight average molecular weight by 5.0% with the addition of a cross-linking agent. Rheological studies on the materials showed that the addition of a cross-linking agent increased the storage modulus and viscosity, while reducing the tan δ value. Using microcellular injection molding, cross-linked thermoplastic polyurethane could be foamed to a minimum density of 0.159 g/cc at the higher end of the processing window, as compared with a minimum density of 0.193 g/cc for pure thermoplastic polyurethane foam. Scanning electron microscope analyses of the foamed parts showed a bimodal foam structure for thermoplastic polyurethane with a cross-linking agent and a more integral foam structure with less cell coalescence even at higher density reductions.

Advances in microcellular injection moulding

“…96 Cross-linking agents have also shown to increase the molecular weight, storage modulus and viscosity of thermoplastic polyurethane thereby increasing melt strength when foamed in the MIM process. 97 Carbon nanotubes. Li et al 98 have investigated the resulting MIM cell morphology and mechanical properties of polyetherimide with multi-walled carbon nanotubes (MWCNT) fillers.…”

Microcellular foaming by using subcritical CO2of crosslinked and non-crosslinked LDPE/clay nanocomposites

“…37,38 By increasing the crosslinking degree (that is, by increasing the gel content), it is also possible to increase the polymers melt strength and improve their extensional rheological properties. 39,40 As a consequence, the foamability of the polymer matrices is also enhanced, leading to important reductions in the reachable density range. 41,42 The two main methods used to crosslink a polymeric matrix are electron beam irradiation and chemical crosslinking by using organic peroxides.…”

A Solvent System Involved Fabricating Electrospun Polyurethane Nanofibers for Biomedical Applications

“…Nanofibers have been widely used in tissue engineering and regenerative medicine [ 1 , 2 , 3 ], and electrospinning is one of the most convenient and controllable methods to manufacture nanofibers. Thermoplastic polyurethane (TPU) is one type of polymer with excellent properties, such as high strength, high toughness, durable wear resistance and good oil resistance that has been used in textile, food, national defense and other industries [ 4 , 5 , 6 ]. Because of their excellent biodegradability and biocompatibility, TPU nanofibers have been widely used in biomedical applications [ 7 , 8 ].…”