Thermomechanical Characterization of a Series of Crosslinked Poly[ethylene-co-(vinyl acetate)] (PEVA) Copolymers

Abstract

Crosslinked poly[ethylene-co-(vinyl acetate)] (cPEVA) has been recently introduced as a polymer material, which can be functionalized with various shape-memory effects by solely altering the thermomechanical treatment called programming.In this study two series of cPEVAs with different vinyl acetate contents of 18 wt% (cPEVA18) and 28 wt% (cPEVA28) comprising different crosslink densities were investigated by differential scanning calorimetry (DSC) and dynamic mechanical thermal analysis (DMTA) in the temperature range of -130 °C to 120 °C. DMTA tests were performed in torsion mode, because such movements are highly relevant in the context of complex shape changes in shape-memory polymer based devices. Finally, the obtained DMTA results were compared with DMTA conducted in tension mode. Swelling experiments revealed a gel content in the range from 81% to 90% for cPEVA18 samples while for cPEVA28s a complete conversion was observed. The degree of swelling was found to decrease substantially with increasing crosslink density for both cPEVA series.The influence of VA content and extent of crosslinking on the appearance of the respective melting (Tm) and glass transition (Tg) as well as the thermomechanical properties of cPEVA systems could be demonstrated by discussing both DSC and DMTA results. The temperature range of mechanical stability correlates with the VA content and is determined by decreasing Tm values. The cross links do barely alter the stiffness of a PEVA up to the Tm rang, but lead to constant mechanical rigidity in the rubbery range above Tm.

Influence of Compression Direction on the Shape-Memory Effect of Micro-Cylinder Arrays Prepared from Semi-Crystalline Polymer Networks

“…Shape-memory polymers (SMPs) are a prominent class of thermo-sensitive materials, which are capable of active movements. While in the last decade the majority of SMP research was focused on the investigation of macroscopic effects [1], more recently micro-and nanostructured SMP films have been explored as novel type of intelligent surface [2][3][4][5][6][7][8][9]. In this context smart films have been reported showing i.e.…”

“…In this context smart films have been reported showing i.e. a switchable wettability [2] or adhesion [3,9], allow controlled changes in optical elements [4,5], can be applied as intelligent microfluidics [6] or utilized as active cell culture substrates [7,8].…”

“…(cPEVA) with a vinyl actetate content of 18 wt% having a broad melting transition in the temperature interval from 30 to 85 °C [9] related to crystalline polyethylene domains, was selected as polymer matrix exhibiting excellent shape-memory properties [10]. A soft lithography approach was chosen for fabrications of cPEVA microstructured films comprising arrays of micro-cylinders with different diameters of 10, 25, and 50 µm.…”

“…For crosslinking of the PEVA/DCP mixture the temperature was raised to 220 ºC and kept for 30 minutes. After cooling to 0 °C the PDMS mask was removed and microstructured cPEVA films with a thickness in the range of 400 to 500 µm and different micro-cylinder arrays with diameters of 10 µm (cPEVA_10), 25 µm (cPEVA_25), and 50 µm (cPEVA_50) were obtained.The obtained three cPEVA films were characterized with respect to their gel content (G) and thermal properties according to the methods described in Ref[9]. G was determined after extraction with toluene for 24 hours at 80 ºC, while differential scanning calorimetry (DSC) experiments were performed with a Netzsch DSC 204 (Selb, Germany) with a constant heating and cooling rate of 10 ºC•min -1 to analyze the melting and crystallization temperatures (Tm and Tc).…”

Implications of Thermal Annealing on the Benzene Vapor Sensing Behavior of PEVA-Graphene Nanocomposite Threads

“…Poly(ethylene- co -vinylacetate) (PEVA) is a semicrystalline polymer at room temperature, and has been studied extensively for use in vapor sensors, 1–3 wire insulation, 4 shrinkable and moldable parts, 5,6 and thermal conduction materials. 7 PEVA is a copolymer, with a reported glass transition temperature ( T g ) near −30 °C 8 and a melting temperature ( T m ) in the range of 85–88 °C.…”