The role of functional polymers in rubber powder/thermoplastic composites

548 2017, 62, nr 7–8 The role of functional polymers in rubber powder/ thermoplastic composites*) Eduard V. Prut1), **), Lyubov A. Zhorina1), Larisa V. Kompaniets1), Dmitrii D. Novikov1), Arkadii Ya. Gorenberg1) DOI: dx.doi.org/10.14314/polimery.2017.548 Abstract: Low density polyethylene (LDPE), ethylene-vinyl acetate copolymer with 10–14 wt % (EVA-1) and 24–30 wt % vinyl acetate (EVA-2) contents, respectively, and ethylene-vinyl acetate-maleic anhydride terpolymer (OREVAC) were combined with rubber powder in the composition range: 100/0, 80/20, 70/30, 50/50, 30/70, 20/80. Two different rubber powders were used: ground rubber tire (GRT) and ethylene-propylene-diene (EPDM) rubber powder (RP), both of which were prepared by high temperature shear deformation. In the case of RP, changes in the crosslink density were also considered. The mechanical properties, melt flow index and morphology of the polymer/rubber powder composites were studied. Specimens were either prepared by compression or, for selected compositions, through injection molding. Improved elongations at break were observed for the OREVAC/rubber powder and EVA/rubber powder composites that were attributed to an enhanced interfacial adhesion between the dispersed rubber particles and matrix polymer. Composites with a rubber powder content as high as 70 wt % still showed good processability and elongation at break values greater than 100 %, which are basic requirements of traditional thermoplastic rubbers. Keywords: rubber powder, thermoplastic polymers, mechanical properties, melt flow index, morphology. Rola polimerów funkcjonalnych w termoplastycznych kompozytach z udziałem proszków gumowych Streszczenie: Polietylen małej gęstości (LDPE), kopolimery etylen-octan winylu z udziałem 10–14 (EVA-1) lub 24–30 % mas. (EVA-2) octanu winylu oraz terpolimer etylen-octan winylu-bezwodnik maleinowy (OREVAC) zmieszano ze sproszkowaną gumą w stosunku 100/0, 80/20, 70/30, 50/50, 30/70, 20/80. Użyto dwa rodzaje proszków gumowych: zmieloną gumę opon samochodowych – GRT i sproszkowany kauczuk etylenowo-propylenowo-dienowy (EPDM) – RP, otrzymywanych w warunkach wysokiej temperatury pod wpływem odkształceń ścinających. W wypadku stosowania RP brano również pod uwagę jego gęstość usieciowania. Badano właściwości mechaniczne, wskaźnik szybkości płynięcia oraz morfologię otrzymanych kompozytów. Próbki do badań przygotowywano metodą wytłaczania, a próbki wybranych kompozycji – także metodą wtryskiwania. Zaobserwowano zwiększenie wytrzymałości na rozciąganie próbek kompozytów proszek gumowy/OREVAC i proszek gumowy/EVA, co wiązało się z efektywniejszą adhezją pomiędzy zdyspergowanymi cząstkami napełniacza gumowego i polimerową matrycą. Kompozyty zawierające więcej niż 70 % mas. proszkowego napełniacza gumowego wykazywały dobrą przetwarzalność, a ich wytrzymałość na rozciąganie była większa niż 100 %, co spełnia warunek stawiany tradycyjnym termoplastycznym kauczukom. Słowa kluczowe: proszek gumowy, polimery termoplastyczne, właściwości mechaniczne, wskaźnik szybkości płynięcia, morfologia. One of the various problems of the 21st century is waste disposal management [1–4]. A great deal of waste rubber is produced every year in the world. The main sources of waste rubber products are discarded tires, pipes, belts, Russian Academy of Sciences, Semenov Institute of Chemical Physics, Kosygina 4, Moscow, 119 991 Russia. *) This material was presented at 9th International Conference MoDeSt 2016, 4–8 September, 2016, Cracow, Poland. **) Author for correspondence; e-mail: 1) shoes, edge scraps and waste products that are produced in rubber processes and others. The three-dimensional crosslinked structure of waste rubber makes it infusible, insoluble and difficult to recycle. Typical recycling methods have been developed to treat waste rubber: combustion, landfilling, biodegradation, and recycling. Among them, recycling is the most attractive. Recycling is a major issue for most plastic processors and waste disposal authorities in the new century. However, the technology for recycling rubbers is complex and costly. POLIMERY 2017, 62, nr 7–8  549 The choice of the process is based on the requirements of the final product, such as particle size distribution and structure of the particles. The search for better technologies that will allow larger quantities of waste rubber to be incorporated into new products continues and several new approaches have been successful. One of the promising methods developed in the last two decades is high temperature shear deformation (HTSD) [1, 5]. This technique is based on the degradation of a material in a complex strained state by the action of uniform compression pressure and shear forces under elevated temperatures. HTSD makes it possible to obtain fine powders, thus allowing the valuable properties of elastomer materials to be realized to a considerable extent. Considerable efforts have been devoted to finding new applications for ground rubber tire (GRT). Fine GRT particles may be used as fillers and property modifiers in thermoplastic, elastomer and thermoset blends. Although the use of GRT as a filler in polymer composites is a potentially attractive approach, it is fraught with a number of difficulties. Karger-Kocsis et al. [4] recently published a comprehensive review regarding the difficulties of producing high quality GRT filled compounds. The mechanical properties of such composites depend on the content of GRT, polymer matrix type, adhesion between the GRT and the polymer matrix, as well as the particle size and their dispersion and interaction between GRT and the matrix. However, the incorporation of GRT particles into a number of polymer matrices significantly deteriorates the mechanical properties of the composites due to very weak interfacial adhesion between the GRT particles and the matrix-forming polymer [4–12]. The effect of mixing conditions on the mechanical properties of thermoplastic rubbers based on isotactic polypropylene (IPP) and GRT prepared from tread rubber by the method of HTSD has been studied [13]. Melt blending of IPP and GRT was used in a Brabender internal mixer at 190 °C for 10 min (rotor speed of 100 rpm) and 1 2 3 400 600 30 300 εb , % 60 σb, MPa 900 E, MPa 500 90 1200 0 0.0 the method of HTSD in a rotor disperser (temperature 190 °C). The mechanical properties of the blend were shown to be independent of mixing conditions (Figs. 1, 2). Depending on the amount of crumb rubber, three regions that differ in the mechanism of deformation of thermoplastic rubbers are distinguished: < 0.1, 0.1–0.75, and > 0.75 parts by volume. According to Bazhenov et al. [9], the successive change of deformation a mechanism from plastic macro-heterogeneous deformation to brittle fracture and then to macro-homogeneous deformation takes place when the GRT content in the blend increases. Thus, the content of GRT is an important factor, which influences the structure a (...truncated)