Understanding the relationship between multiphase structure and electromechanical property of thermoplastic dielectric elastomers is significantly important in the developments of high-performance and novel dielectric elastomers. In this work, we fabricated a series of aliphatic polyurethane elastomers (PUEs) based on hydroxyl-terminated butadiene-acrylonitrile copolymer (HTBN), hexamethylene diisocyanate (HDI), and various lengths of linear aliphatic diols and investigated effect of their microstructure and morphology on dielectric and electromechanical properties. The FTIR, WAXS, SAXS, and viscoelastic AFM results showed that the PUEs existed in crystalline phase, hard domain (HD) and soft domain (SD) phases composed HD-rich region and few HDs and SD composted SD-rich region by crystallization and microphase separation. Also, the crystal morphology and crystallinity of PUEs are strongly influenced by the length of chain extender due to the chain extender adopting various conformations by hydrogen bonding. The mechanical and electric fields induced responses of segment motions in PUEs at below room temperature were relative to the constrained SS motions from HD-rich and SD-rich regions. The electric field induced strain of PUEs was actuated by both Maxwell stress and electrostriction effect, of which contribution of electrostriction effect was above 64% in total actuation strain. In addition, we found that the effect of electrostriction on the actuation strain played an important role in improving the actuation strain of PUEs at lower electric field. Our results showed that the dielectric and electromechanical properties of PUEs can be adjusted by controlling the crystallization and microphase separation.
The objective of this study was to investigate the feasibility of using polyurethane (PU) foam wastes obtained from automobile shredder residue (ASR) in wood composite panel (fiberboard) production. PU foam wastes from ASR were picked by hand, cleaned by water and acetone, grounded into powders of two sizes (60 mesh and 120 mesh), and dried to remove moisture. The PU powders were characterized by stereomicroscope and then partially replaced pMDI resin at percentages of 10%, 20%, 30%, 40%, and 50% (based on the weight of pMDI resin). The PU powders were mixed with wood fibers to make fiberboards. The results showed that the addition of PU powders increased both the physical and mechanical properties of fiberboards. At replacing percentages from 5% to 30%, the properties of fiberboards increased. However, further increase of replacing percentages (from 30% to 50%) resulted in lower properties of fiberboard. When observed at a magnification of 125 times by a stereomicroscope, PU powders of 60 mesh had more foam features while PU powders of 120 mesh had more particle features. The fiberboards bonded by pMDI resin and PU powders of 120 mesh had better water resistance and mechanical properties than those bonded by pMDI and PU powders of 60 mesh. The use of PU powders in fiberboard production provided a new possible way of recycling PU foam wastes. The fiberboard has advantages of formaldehyde-free, better water resistance, higher mechanical properties, and lower material cost.
The objective of this study was to investigate the feasibility of recovering the polyols from the polyurethane (PU) foam obtained from waste upholstered furniture (sofa) by chemical decomposition using the propylene glycol (PPG) as the decomposing solvent and sodium hydroxide (NaOH) as the catalyst, respectively. The effects of temperature (180°C and 200°C), reaction time (0.5, 1, 1.5, 2, 2.5, and 3 hours), and PPG/PU weight ratio (2:1, 3:1, and 4:1) on the decomposition reaction and the physicochemical properties of the recovered polyols, such as hydroxyl number, viscosity, and amine number were investigated. Higher temperature and PPG/PU weight ratio promoted the PU decomposition reaction and resulted in lower viscosity, higher hydroxyl number, and higher amine number of the recovered polyols. The hydroxyl number and amine number increased as the reaction progressed, while the viscosity decreased. Once the reaction was completed, little change was observed for the hydroxyl number and viscosity of the recovered polyols. The recovered polyol obtained at 200°Cand PPG/PU weight ratio of 3:1 showed about the same length of time for the reaction, as well as the physical properties to that obtained at 180°C and PPG/PU weight ratio of 4:1. These recovered polyols had similar hydroxyl number and viscosity to those of commercial polyol used for PU coatings, elastomers, adhesives, and sealants.
The objective of this study was to investigate the feasibility of using recycled polyols as part of the binder system for wood panels (fiberboard). PU foam wastes from disposed insulation materials were collected, processed, and chemically decomposed by agent to obtain the recycled polyol. The recycled polyol was mixed with a commercial polyol at various weight ratios (0: 100, 20: 80, 40: 60, 60: 40, 80: 20, and 100: 0) to prepare a series of polyol mixtures. Then, the obtained polyol mixtures were then sprayed successively with pMDI resin at various pMDI/polyol mixtures weight ratios (100: 0, 75: 25, and 50: 50) onto wood fibers to prepare fiberboards. The effects of recycled polyol/commercial polyol weight ratio and pMDI/polyol mixture weight ratio on physical and mechanical properties of bonded fiberboards were evaluated. The results showed that the addition of recycled polyol into a commercial polyol helped improve the IB, MOR, and MOE strength of fiberboard, but their effects on water resistance of fiberboard were minor. With the increase of percentage of polyol mixture in pMDI/polyol mixture, the properties of fiberboard presented a trend of decreasing. When the recycled polyol/commercial polyol weight ratio was 40: 60 and the pMDI/polyol mixture was 25: 75, the bonded fiberboard had the overall best physical and mechanical performances. The application of decomposed PU foams in fiberboard production provided a new possible way of recycling polymer wastes.
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