Thermo-responsive shape memory properties based on polylactic acid and styrene-butadiene-styrene block copolymer

This study aims to compare thermal, mechanical, and shape memory behavior of polylactic acid (PLA) blended with different structures of styrene-butadiene-styrene block copolymer (SBS), namely linear SBS (L-SBS), and radial SBS (R-SBS). The amount of L-SBS and R-SBS added was varied between 10 and 70 wt%, and the blending process was carried out using an internal mixer at 180°C before the shaping process by the compression molding. An improvement in the degree of crystallinity was observed across the entire composition range with less pronounced transition temperature change. Tensile strength and modulus of PLA/L-SBS blends were higher than PLA/R-SBS blends across all composition ranges. The results also revealed that the shape fixing ratio (R_f) and recovery ratio (R_r) of PLA/L-SBS were higher than PLA/R-SBS, with PLA70/SBS30 showed the best shape memory behavior. The morphology characteristics of the blend were also examined with the scanning electron microscope.     

Ethylene-propylene diene monomer-based polymer composite for attenuation of high energy radiations

Radiation shielding composites of ethylene-propylene diene monomer (EPDM), reinforced with tungsten (W) and barium sulphate (BaSO₄) in different filler weight (wt%) were synthesized. The effects of W and BaSO₄ on gamma and neutron attenuation properties of the composites were studied by experimental methods using ¹³⁷Cs, ⁶⁰Co and ²⁵²Cf radioactive sources. EPDM composites with W and BaSO₄ fillers were also investigated for filler dispersion using scanning electron microscopy and X-ray radiograph. The experimental results revealed that the incorporation of W and BaSO₄ significantly improved the radiation attenuation properties of the EPDM composites. It was observed that the attenuation properties of the composite material increases with higher concentration of the filler. The half-value layer (HVL), tenth value layer thickness and relaxation length of the composites were found to decrease with increasing concentration of the filler. The results also showed that the attenuation behaviour of 50 wt% BaSO₄ filled polymer composite is comparable to that of the composite with 25 wt% W. The developed composite with 75 wt% W filler exhibited the maximum radiation attenuation with lowest HVL thicknesses.     

Based on transalkylation reaction the rearrangeable conventional sulfur network facile design for vulcanized diolefin elastomers

Achieving the reversibility of conventional sulfur crosslinking network is beneficial for the sustainability of rubber products. However, sulfur crosslinking network has been considered as an irreversible network. Here, natural rubber (NR) is chosen as an example and trimethylsulfonium iodide (TMSI) can enable the transalkylation reaction between aliphatic sulfonium salts and the alkyl chains of vulcanized NR, which further realizes the rearrangements of sulfur crosslinking network in the elastomers. Such rearrangement reaction enhances the interfacial adhesion and fuse the fractured surface of vulcanized NR. Moreover, the rearrangements of sulfur crosslinking network induced by TMSI conforms to the characteristics of vitrimer network. This work solves the rearrangement problem of conventional sulfur crosslinking network, which is beneficial for the sustainability of rubber products.     

Evaluation of the role of devulcanized rubber on the thermomechanical properties of expanded ethylene-propylene diene monomers composites

Various amounts of both devulcanized (DR) and non-devulcanized (NDR) recycled rubber were melt compounded with a virgin ethylene-propylene diene monomer (EPDM) rubber. The resulting compounds were then expanded by using azodicarbonamide. The role played by the presence of DR or NDR on the thermomechanical properties of the obtained materials was evaluated. Electron scanning microscope micrographs highlighted that DR particles were better encapsulated within the EPDM matrix with respect to the corresponding NDR ones. Moreover, a better interfacial adhesion was observed with DR, probably due the re-vulcanization process in which the free crosslinking sites that typically characterize DR could form linkages with the EPDM matrix. Tensile impact behavior of expanded EPDM/recycled rubber blends highlighted a strong improvement of the normalized total absorbed energy, of the normalized impact strength and of the elongation at break with respect to the neat expanded EPDM for all the investigated compositions, and especially with a DR content of 20 wt%. The preparation of expanded EPDM containing considerable amounts of devulcanized rubber was, therefore, demonstrated to be a practical route to reduce the costs and improve the properties and the environmental sustainability of rubber products.     

Morphology and properties of poly(ethylene terephthalate) and thermoplastic polyester elastomer blends modified in the melt by a diisocyanate chain extender and filled with a short glass fiber

The structural features and rheological, mechanical, and relaxation properties of poly(ethylene terephthalate) (PET) blends with 7–50 wt % polyester thermoplastic polyester elastomer (TPEE), a block copolymer of poly(butylene terephthalate) and poly(tetramethylene oxide), chemically modified by a diisocyanate chain extender (CE) and reinforced with 30% glass fibers (GF) were studied. The composites were obtained by reactive extrusion with a twin‐screw reactor–mixer with a unidirectional rotation of screws. The molecular–structural changes in the materials were judged against data provided by differential scanning calorimetry, scanning electron microscopy, relaxation spectrometry, and rheological analysis of the melts. Regardless of the TPEE concentration in the blends with GF‐reinforced PET, the addition of CE resulted in the growth of the indices of the mechanical properties at straining, bending, and impact loading and an increase in the melt viscosity. In addition, an increase in the average length of short GFs in the composites and an intensification of interphase adhesion in the polyester binder–GF surface system were observed. The introduction of CE promoted a slowdown in PET crystallization in the composites and intensified the interphase adhesion in the binder–GF system at temperatures higher and lower than the PET glass‐transition temperature. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018 , 135, 45711.     

Investigation of the effect of foaming process parameters on expanded thermoplastic polyurethane bead foams properties using response surface methodology

Expanded thermoplastic polyurethane (ETPU) bead foams were fabricated by batch foaming with supercritical CO₂ as blowing agent. On the basis of single factor investigation, the response surface methodology based on Box‐Behnken Design was used to investigate the influences of saturation pressure, temperature, and soaking time and their interactions on foaming behavior of ETPU. The results showed that saturation temperature was the most significant parameter affecting the expansion ratio, shrinkage ratio, and cell morphology of ETPU. Moreover, there was an interaction effect between saturation temperature and soaking time, wherein the expansion ratio of ETPU was more sensitive to change of soaking time at higher temperature. As the soaking time increased, the shrinkage of ETPU increased firstly and then leveled off, and the cell diameter decreased significantly. By applying the response surface methodology optimization, ETPU bead foams with final expansion ratio of 8.04, mean cell diameter of 74.2 μm, and average cell density of 1.46 × 10⁷cell/cm³ can be obtained while the optimum conditions at saturation pressure of 15 MPa, saturation temperature of 100 °C and soaking time for 60 min. In addition, the dual melting peak of ETPU characteristics demonstrated that it is suitable for steam‐chest molding technology. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018 , 135, 46327.     

Tuning the properties of segmented polyurea by regulating soft‐segment length

Polyurea is being widely advocated as a “retrofit” coating on structures, which mandate protection against blast. The physical properties of polyurea can be tuned by judicious choice of reactants, and the processing methodology employed for its preparation. The purpose of this study is to establish the dependence of material properties on the soft segment length in polyurea. Polyurea formulations were prepared by reaction of commercially available isocyanate prepolymer with poly(propylene oxide) based amines of varying molecular weights (230–2000 g/mol). The effect of increasing the soft segment length on the mechanical properties of polyurea under both quasi‐static as well as dynamic conditions was determined. Ductility was found to increase proportionally with increasing soft segment length, with a concomitant decrease in the tensile strength. All the compositions exhibited sub‐ambient glass transition temperature, which was found to reduce with increasing soft‐segment length. Time–temperature superposition principle was used to arrive at master curves for all compositions. The frequency essential to initiate the process of dynamic “rubber to glass” transition was found to be directly proportional to the soft segment length. All the formulations were found to be capable of exhibiting an elastomeric response even under high frequencies typical of blast loadings. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018 , 135, 46284.     

Tire tread compounds with reduced rolling resistance and improved wet grip

The aim of this work is to investigate the replacement of carbon black by silica‐organosilane coupling agent system and the number of processing steps on the mechanical properties, rolling resistance, and wet grip of truck tire treads. Eight compounds were prepared: two formulations based on carbon black, five formulations with the partial replacement of carbon black by a silica‐organosilane coupling agent system, and one formulation with the total replacement of carbon black with silica. The rolling resistance decreased by 10% and the wet grip increased by 18.5% for the compound with 15 phr of silica, 3 phr of organosilane, and three processing steps compared to the standard compound. The processing steps also promoted an improvement in these properties for the composition with 50 phr of carbon black. The partial use of silica reduced the abrasion loss, thus confirming the durability of the compound. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134, 45334.     

Synergistic effect of SBS and trimethylopropane trimethacrylate (TMPTMA) on dynamically vulcanized SEBS/PP blends

The SEBS/PP thermoplastic vulcanizates (TPVs) were prepared by melt blending. Di‐tert‐butyl peroxide (DTBP) was used as the curing agent in combination with trimethylopropane trimethacrylate (TMPTMA) and poly(styrene‐b‐butadiene‐bstyrene) (SBS) as the coagents for the curing process. The synergistic effect of TMPTMA and SBS on the structure and properties of TPVs was studied by means of FT‐IR, DSC, torque rheometer, and universal testing machine. Both SEBS and PP crosslinked and the network structure formed under the participation of TMPTMA and SBS. Compared with the sole addition of the coagent, simultaneous loading of both TMPTMA and SBS could provide the TPVs with better solvent‐resistance and excellent mechanical properties. The crosslinking mechanism of the TPVs was also proposed. The slight lower value of T_m for the TPVs indicated the improved miscibility between PP and SEBS due to the crosslinking reaction. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134, 44392.     

Adhesion at Poly(Butylacrylate)–Poly(Dimethylsiloxane) Interfaces

We present an investigation of the adhesion modulation mechanisms of silica-like nanoparticles (MQ resins) incorporated in polydimethylsiloxane (PDMS) elastomers and acrylic adhesives. The Johnson-Kendall-Roberts (JKR) test has been used to gain information on the both zero velocity and the velocity dependence of the adhesive strength, avoiding as much as possible contributions to the adhesive strength of bulk dissipation in the adhesive (which is not the case with peel tests). As the incorporation of the MQ resins into the elastomers deeply affects their own mechanical properties, the loading and unloading curves of small poly(butylacrylate) (PBA) lenses on either PDMS elastomers, adsorbed PDMS and pure MQ resin layers are compared in a systematic manner. The PBA chains are observed to have a neat affinity for the MQ resin nanoparticles. When MQ resins are present at the interface, they tend to prevent facture propagation, thus producing a larger deformation of the PBA lens. The modulation of adhesion is then dominated by the corresponding dissipation inside the acrylic adhesive.