Ultrasonic Devulcanization of Used Tires and Waste Rubbers

Journal of Elastomers & Plastics

2013

Ultrasonically aided extrusion of natural rubber (NR), styrene butadiene rubber (SBR), and NR/SBR blends with ratio of 70/30, 50/50, and 30/70 were carried out at various ultrasonic amplitudes up to 10 mm. A die pressure of NR and NR/SBR blends continuously decreased with increase of ultrasonic amplitude, while that of SBR showed a slight increase with increase in amplitude from 5.0 to 7.5 mm due to a dominant effect of SBR gel formation. Complex dynamic viscosity, minimum and maximum torque of curing curves of NR, SBR, and NR/SBR blends, and cross-link density and gel fraction of their vulcanizates were decreased by the ultrasonic treatment at an amplitude of 10 mm, due to the molecular chain scission. The latter also led to a decrease in the hardness, modulus at a strain of 100%, and abrasion resistance of NR and NR/SBR blends. However, the modulus and abrasion resistance of SBR showed an improvement at amplitude of 7.5 mm, due to a dominant effect of gel formation. Both the tensile strength and elongation at break of ultrasonically treated NR/SBR blends showed a maximum at amplitude of 5.0 mm, with the modulus at a strain of 100% not being affected. Morphological studies using the phasecontrast optical microscope and atomic force microscopy showed a reduction in the size of rubber phases and a better homogeneity of NR/SBR blend by the ultrasonic treatment at amplitude of 5.0 mm. Accordingly, the increase in both the tensile strength and elongation at break of ultrasonically treated NR/SBR blends at an amplitude of 5.0 mm is mainly ascribed to the lower size of rubber phases and improved uniformity of blend caused by the ultrasonic treatment.

Section: Introductionmentioning

confidence: 99%

Natural rubber/styrene butadiene rubber blends prepared by ultrasonically aided extrusion

Choi

Journal of Elastomers & Plastics

2013

“…During the past two decades, Isayev and co‐workers developed ultrasonic‐assisted extrusion technology to devulcanize various rubbers . Decrosslinking of XHDPE was also attempted, but a severe thermal degradation occurred due to significant overheating from the dissipation of ultrasonic energy leading to inferior properties of the decrosslinked XHDPE .…”

Section: Introductionmentioning

confidence: 99%

Decrosslinking of crosslinked high‐density polyethylene via ultrasonically aided single‐screw extrusion

Polymer Engineering & Sci

Huang

2013

A novel environmentally friendly process for decrosslinking of the peroxide crosslinked HDPE (XHDPE) via ultrasonic assisted single (SSE) is developed and its process characteristics are established. The specific ultrasonic energy decreases with the flow rate and increases with the ultrasonic amplitude, while die pressure increases with the flow rate and decreases with the ultrasonic amplitude. Application of ultrasonic treatment during extrusion enables an increase of productivity. Gel fraction, crosslink density, dynamic and mechanical properties, and thermal behavior of the virgin HDPE, XHDPE, and decrosslinked XHDPE are measured. Gel fraction and crosslink density of the decrosslinked XHDPE are decreased with increasing flow rate and ultrasonic amplitude. A unique linear relation between the normalized gel fraction and the normalized crosslink density is found, regardless of the type of extruders and processing conditions. SEM images reveals that the decrosslinked XHDPE is a composite of submicron size gel particles embedded in its sol matrix. The sol extracted from the decrosslinked XHDPE exhibits a higher complex viscosity and higher level of branching than the virgin HDPE. An increase of the ultrasonic amplitude leads to a decrease of the complex viscosity, storage and loss moduli, and an increase of the loss tangent of the decrosslinked XHDPE. The thermal behavior and mechanical properties of the decrosslinked XHDPE show a weak dependency on processing conditions. At some processing conditions, mechanical properties of the decrosslinked XHDPE are close or higher to those of XHDPE.

“…The ultrasonically devulcanized rubbers can be reprocessed as virgin rubbers and revulcanized leading to mechanical performance of vulcanizates affected by the chemical structure and type of rubbers [8][9][10][11]. The chemical structure of XPE is similar to that of rubber vulcanizates, therefore ultrasonic decrosslinking of peroxide-crosslinked HDPE was attempted by ultrasonically aided SSE [12].…”

Section: Introductionmentioning

confidence: 99%

“…Ultrasonic devulcanization of various rubber vulcanizates are conducted by ultrasonically aided extrusion [8][9][10][11]. During ultrasonically aided extrusion of rubbers, the ultrasonic horn is in the direct contact with flowing rubbers.…”

Section: Introductionmentioning

confidence: 99%

Comparison between decrosslinking of crosslinked high and low density polyethylenes via ultrasonically aided extrusion

Huang

2015

Polymer

Please cite this article as: Huang K, Isayev AI, Comparison between decrosslinking of crosslinked high and low density polyethylenes via ultrasonically aided extrusion, Polymer (2015), AbstractAmong various polymer wastes, management of crosslinked plastics is a major environmental problem requiring a solution. Among various crosslinked plastics, recycling of crosslinked polyethylenes is of a great importance due to the presence of a three-dimensional network. To solve this problem, novel environmentally friendly technologies for decrosslinking of the crosslinked polymers are developed based on ultrasonically assisted single (SSE) and twin screw (TSE) extruders. In particular, decrosslinking of peroxide crosslinked high-density polyethylene (XHDPE) and low-density polyethylene (XLDPE) by means of an ultrasonic SSE and TSE is investigated. Barrel pressure, die pressure and ultrasonic power consumption during extrusion are recorded. Swelling, rheological, thermal analysis and tensile tests are used to elucidate the structure-property relationships of decrosslinked XHDPE and XLDPE. The frequency dependencies of the storage and loss moduli, complex viscosity and tangent loss of XHDPE, XLDPE and their decrosslinked networks are described by the post critical gel model with its parameters correlated with gel fraction and crosslink density. The dynamic, thermal and tensile properties of the decrosslinked XHDPE and XLDPE are greatly affected by the type of preferential bond breakage. It was found that the decrosslinking of XLDPE is more difficult than that of XHDPE. An analysis based on the Horikx function reveals a highly preferential breakage of crosslinks during decrosslinking of XHDPE. In contrast to decrosslinking of XHDPE, the presence of long-chain branching in XLDPE is found to lead to the breakage of its main chains during decrosslinking. An improvement and a reduction in mechanical properties of decrosslinked XHDPE and XLDPE are, respectively, observed in comparison with those of virgin XHDPE and XLDPE. Such differences in behavior are due to the occurrence of a highly preferential breakage of crosslinks in XHDPE and the breakage of main chains in XLDPE during ultrasonic decrosslinking. Graphic AbstractStress-strain curves of HDPE, LDPE, XHDPE and XLDPE (a) and decrosslinked XHDPE (b) and XLDPE (c) by SSE and TSE with and without ultrasonic treatment.