No abstract

The devulcanization reactions of ground tire rubber (GTR) and thermoplastic elastomer (TPE) mixtures performed during the melt‐extrusion process through the induction of high shear stress by increases in the screw rotation speeds and reaction temperatures were investigated in this study. The results show that the high shear stress induced crosslink breakage and/or chain scission of GTR; this led to decreases in the gel contents and Mooney viscosities of the devulcanized GTR(DGTR)/TPE blend and decreases in the sizes of the unfused gel particles in the revulcanized blends of styrene–butadiene rubber [SBR/(DGTR/TPE)]. When the main composition of GTR was natural rubber, its allylic unit structures in the main chains were susceptible to degradation. Although the main composition of GTR was SBR, its main chains contained lower contents of double bonds and were more stable; this led to significant changes in the gel contents and Mooney viscosities of the devulcanized blend and in the mechanical properties of the revulcanized SBR/(DGTR/TPE) blend. The ethylene–propylene–diene monomer (EPDM4770) rubber had better compatibility with GTR than the ethylene/1‐octene copolymer and also had a higher molecular weight than that of EPDM3745. This led to a lower gel content and a higher Mooney viscosity in the devulcanized blend and higher mechanical properties in the revulcanized SBR/(DGTR/EPDM4770) blend. The alkylphenol polysulfide 420 and 450 accelerated the devulcanization reaction and prevented the crosslinking reaction; this led to significant increases in the mechanical properties of the revulcanized SBR/(DGTR/TPE) blend. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2013

Grafting of maleic anhydride (MAH) onto high density polyethylene (HDPE) performed in the melt state through ultrasonic initiation by a laboratory‐scale ultrasonic extrusion reactor was studied in this paper. The effect of sonic intesity on the amount of grafted MAH, viscosity‐average molecular weight and melt flow index of the grafted product was investigated. The results show that the ultrasonic waves can obviously decrease the molecular weight of the grafted product and cause the increase of the amount of grated MAH, implying that the grafting reaction consists of the chain scission and the grafting reaction of the produced macroradicals with MAH. The percentage of grafting of the product amounts to 0.6%; its melt‐flow index is between 0.5 and 2.0 g/10 min, depending upon ultrasonic intensity, MAH content and grafting temperature. Compared with the method of peroxide initiation, in this method the crosslinking reaction can be prevented easily through the allocation of ultrasonic intensity. The mechanical properties of the improved HDPE/GF composite produced by ultrasonic initiatives are higher than in those produced by peroxide initiatives.

The devulcanization reaction of styrene–butadiene rubber (SBR) based ground tire rubber (GTR) in GTR/ethylene–propylene–diene monomer rubber (EPDM) blend was investigated through a compound‐induced reaction by increasing screw rotation speed and being in the presence of subcritical water. The effects of temperature, pressure, screw rotation speed, or promoting agents on the gel content, Mooney viscosity, and Fourier transform infrared spectra of the sol of the devulcanized blends (devulcanized ground tire rubber (DGTR)/EPDM) were measured, and the mechanical properties and microstructures of the revulcanized blend ((DGTR/EPDM)/SBR) were characterized. The results show that subcritical water as a swelling agent and reaction medium promotes the devulcanization reaction, increases the selectivity of the crosslink breakage, keeps the extrusion material from oxidative degradation, reduces the gel particle size of the devulcanized blends, and significantly improves the mechanical properties of the revulcanized SBR/(DGTR/EPDM) blends. In subcritical water, the suitable promoting agents (alkylphenol polysulfide 450, hydrogen peroxide H2O2, or 450/H2O2) accelerate the devulcanization reaction, keep the double bond content, and lead to further decrease of the gel content and Mooney viscosity of the devulcanized blends and further increase of the mechanical properties of the revulcanized SBR/(DGTR/EPDM) blends. Especially the compound promoting agent (450/H2O2) improves the selectivity of the crosslink breakage in devulcanization of SBR‐based GTR. When 450/H2O2 is added as a compound promoting agent at the best reaction condition in subcritical water (200°C, 1.6 MPa and 1000 rpm), the tensile strength and elongation at break of the revulcanized SBR/(DGTR/EPDM) blends reach to 85.4% and 201% of vulcanized SBR (24.0 MPa, 356%), respectively. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 130: 1845–1854, 2013

No abstract

No abstract

In this work, the devulcanization reaction of isobutylene-isoprene rubber (IIR)-based ground bladder rubber (GBR) in GBR/ethylene-propylene-diene monomer (EPDM) blend was investigated through a co-rotating twin-screw extruder. The influences of subcritical fluids (blank sample, water, ethanol, and n-propanol) and temperatures (160 C, 180 C, and 200 C) were investigated. The results confirmed the effectiveness of subcritical fluids in decreasing the gel content. Moreover, gel permeation chromatography analysis demonstrates that the devulcanizing processes with subcritical fluids are more homogeneous, making the molecular weight of sol detached from the devulcanized blend more uniform. Proton nuclear magnetic resonance spectra confirm that the reactivity of devulcanization of subcritical ethanol was the best. The optimal extrusion temperature for devulcanization is 180 C, at which the mechanical properties of the revulcanized IIR/(devulcanized ground bladder rubber [DGBR]/ EPDM) blends achieve the best state. When promoting agent alkylphenol polysulfide (450) works with the assistance of subcritical ethanol at the best reaction condition (180 C, 2.0 MPa, and 500 r min À1), the tensile strength and elongation at break of the revulcanizate retain 94.7% and 110.2% of vulcanized IIR (15.91 MPa, 483.62%), respectively.

No abstract