Processing and Characterization of Microwave and Ultrasonically Treated Waste-EPDM/LDPE Polymer Composites Yeo Joo Hong, 1 Keuk Min Jeong, 1 Prosenjit Saha, 1 Jaechan Suh, 2 Jin Kuk Kim 1 1 Department of Materials Engineering and Convergence Technology, Gyeongsang National University, Gyeongnam, Jinju, 660-701, South Korea 2 Bansuk Industries, Inc., Gyeongnam, Gimhae, 621-260, South Korea Composites have been prepared from devulcanized waste ethylene propylene diene monomer (W-EPDM) rubber by blending with low-density polyethylene (LDPE) in a twin- screw extruder. W-EPDM was treated separately by opti- mized microwave and ultrasonic radiation. Effect of com- patibilizer such as ethylene octane elastomeric copolymer (POE) on the enhancement of mechanical properties of composites was also studied in addition to the radiation treatment. The enhancement of tensile strength (TS) and elongation at break of composite with microwave-treated W-EPDM were increased up to 41% and 62%. Corre- sponding values were found 44% and 68% for ultrasonic treatment. Higher amount of energy during microwave treatment induced larger and localized cavity formation on the surface of composite results reduction of TS as confirmed from surface morphology study. On the con- trary, encapsulation effect of POE only found to be useful to enhance TS of the composites up to 30% with untreated W-EPDM and LDPE. No significant additional strength increase over microwave and ultrasound treat- ment was found upon using POE. The encapsulation effect of POE disappeared when radiation was applied. FTIR and DMA study revealed the existence of only physi- cal interaction upon microwave and ultrasound treatment. POLYM. ENG. SCI., 00:000–000, 2014. V C 2014 Society of Plastics Engineers INTRODUCTION As a consequence of rapid growth of rubber-based industries, the amount of waste rubber components has also been increas- ing since the last few years. The systematic recycling of large amount of these rubber wastes into value-added end products has become a global challenge for the researchers because of the strong environmental legislations on waste disposal [1]. Rec- lamation and devulcanization of rubber wastes are two most useful methods available for recycling. The differences between these two methods are based on the nature of chemical degrada- tion of the substrate. Reclamation includes the scission of poly- meric chains into lower molecular mass fraction; on the contrary, devulcanization represents the cleavage of crosslinks such as CAS and SAS bonds within rubber waste without affecting the main polymeric chains [2]. It is obvious that devul- canization needs higher energy to break the CAS and SAS bonds in a selective manner. Among the available methods for rubber waste devulcaniza- tion, ultrasonic and microwave treatments are considered to be the promising and ecofriendly technologies in present times. Several studies have been carried out on the recycling of rubber waste using ultrasonic and microwave treatment as an alterna- tive to other existing devulcanization techniques such as thermo- mechanical [3, 4], thermochemical [5, 6], and microbiological processes [7, 8]. It has been reported that the devulcanization of rubber with ultrasound (with frequency interval between 20 kHz to 500 MHz) generally includes the chain cleavage near the middle of the polymer chain due to cavitation of bubbles at negative pres- sure interval during ultrasound irradiation [9]. The formation and collapse of the bubble plays an important role in the degra- dation of polymers in solution. In recent times, several researches have been conducted on the effect of use of ultra- sound devulcanization on ground tire [10, 11], SBR [12], NR [13], PDMS [14], synthetic isoprene [15], silicone rubber [16], and EPDM [17]. The study of ultrasound-assisted devulcaniza- tion of waste rubber carries a great importance as the method can be used as a powerful technology for controlled and contin- uous polymer degradation for obtaining lower molecular fractions. On the contrary, microwave-insisted devulcanization of rub- ber promotes the breaking of crosslinked bonds of rubber due to heat generation during microwave exposure (with frequency between 300 MHz to 300 GHz). The process of microwave- assisted devulcanization of rubber was first developed and patented by Goodyear Tire and Rubber Company in the year 1970 [18]. Since then microwave technology has been widely studied to identify the possible mechanism of materials–micro- wave interaction for rubber devulcanization [5]. Molecules hav- ing polarity are rapidly responded to microwave exposure. Due to the interaction of materials with microwave, the available kinetic energy causes production of frictional heat that is found enough to break the crosslink bonds around the polar particles [19]. Through this principle, vulcanizated or crosslinked rubber- containing polar fillers such as carbon black and silica can be devulcanized by using microwave treatment. However, more effect is observed if the material involved has a greater dielec- tric constant at a specific microwave frequency and power. There are few studies on the microwave-assisted devulcanization of ground SBR scraps [20], bromobutyl rubber [19], and tire rubber [21]. Waste EPDM rubber (W-EPDM) shares a major part of total waste generation from rubber materials as EPDM is widely used as weather strips, automotive tubes, door sealing, gaskets, and other day-to-day appliances. W-EPDM has the potential to be Correspondence to: Jin Kuk Kim; e-mail: rubber@gnu.ac.kr DOI 10.1002/pen.23916 Published online in Wiley Online Library (wileyonlinelibrary.com). V C 2014 Society of Plastics Engineers POLYMER ENGINEERING AND SCIENCE—2014