A developed, eco-friendly, and flexible thermoplastic elastomeric foam from SEBS for footwear application

Abstract

In search of new materials to develop comfortable shoe sole, nowadays the researchers have resorted to the thermoplastic elastomers (TPEs) usually used as cushioning materials for its easy processability and adorable physical properties that can meet both the comfort as well as other functional requirements (i.e. fashion, ultralight, aging, etc.). TPEs are a class of copolymers or physical mixes of polymers and have the morphology of non-miscible blends of elastomer and thermoplastic matrix simultaneously. Low or room temperature elastomeric behavior and high temperature processablitiy makes TPE as a suitable material for developing lightweight and recyclable microcellular foams [1]. Most of the commercial TPE foams for footwear application are developed either from thermoplastic polyurethane (TPU) or ethylenevinyl acetate (EVA) copolymer in which the soft matrix provides sufficient free space for gas absorption whereas the rigid matrix prevents the gas diffusion during foaming process [2][3][4][5][6]. Styrene-(ethylene-cobutylene)-styrene polymers (SEBS) derived from the hydrogenation of styrene-butadiene-styrene (SES) polymers is a typical TPE which shows a better weather resistance, lower compression set, lower density, etc., can be a potential alternative of TPU or EVA [7,8]. SEBS consists of a soft midblock of ethylene-butylene (E-co-B) and hard end-blocks of 948 Abstract. Developing eco-friendly, flexible thermoplastic elastomeric foams based on poly(styrene-(ethylene-co-butylene)styrene) (SEBS) is a challenging task because of its poor melt strength. A promising approach to overcome this challenge is the use of synergistic technologies, such as combination of irradiation, supercritical fluid foaming, and steam-chest molding technologies. Herein, foamed beads were produced from pre-crosslinked SEBS beads using supercritical nitrogen as blowing agent, followed by subsequently efficient steam-chest molding to obtain midsole part. The crosslinking was accomplished under the assistance of electron beam. The rheology properties and foaming behavior reveals that the viscosity and modulus of the matrix increase with the increase of crosslinking resulting from increasing the irradiation dose (ID). With increasing the ID, successful foaming with larger expansion and improved cell morphology was achieved. SEBS bead foams were successfully obtained from 65 kGy-derived pre-crosslinked beads through steam-chest molding which showed a specific gravity of 0.252 g·cm -3 and comparable/superior mechanical properties to/than that of commercial thermoplastic polyurethane (TPU) or ethylene-vinyl acetate copolymer (EVA) foams. Especially, the higher elasticity and resilience of SEBS foams meet well the desirable properties for footwear application which supports SEBS to be an alternative for TPU or EVA.

Improvement of Impact Strength of Polylactide Blends with a Thermoplastic Elastomer Compatibilized with Biobased Maleinized Linseed Oil for Applications in Rigid Packaging

“…The absence of unsaturations in the hydrogenated structure provides excellent thermal and UV resistance [31], which is a key factor in the food packaging industry. In addition, due to its wide range of elasticity and hardness values (depending on the ethylene-butylene segments) and easy processing at relatively low temperatures, it is used in a wide range of sectors such as adhesives, cable coatings, films, toys, household appliances and, increasingly, in the medical and automotive sectors [32,33]. SEBS has been reported to provide improved impact strength and overall ductility in poly(propylene)/poly(styrene) blends as well as in polyamide-based formulations [34][35][36].…”

Development of Poly (Lactide Acid) Foams with Thermally Expandable Microspheres

“…The foaming of polymers is possible mechanically (air dispersion), physically (gas injection, bead foaming, expandable microspheres), and chemically (foaming agents that generate effective gases through thermal decomposition, e.g., in the case of during polyurethane foaming) [1][2][3]. Nowadays, the polymer foam market is growing at an annual rate of about 3-6% [4], mainly because polymer foams have low weight and excellent thermal, acoustic, moisture insulating, and damping properties [5][6][7][8][9][10][11]. Due to the increasingly stringent environmental directives and the reduction/prohibition of single-use products, polylactide acid (PLA) is one of the most important biopolymer candidates to enhance sustainability.…”

Evaluating the cell structure‐impact damping relation of cross‐linked polyethylene foams by falling weight impact tests

“…8 In addition to the industries listed above, the impact damping capability of foams is also exploited by the sports equipment industry, where polymer foams are used in both sportswear and sports mats. For example, shoe soles made of polymer foam reduce the load on the knee joint of runners, 9,10 while protective clothing in motorsports can save lives. In addition, sports mats produced from polymer foams are used in martial arts, jumping, and gymnastics, as the load on the athlete at the moment of landing must be reduced to prevent sports injuries.…”