The surface of ethylene-propylene-diene monomer (EPDM) rubber was treated in N2/Ar and N2/H2/Ar RF plasmas in order to achieve similar or better adhesion properties than NBR (acrylonitrile-butadiene) rubber, nowadays used as thermal protection of rocket chambers. The surface properties were studied by contact angle measurements and by x-ray photoelectron spectroscopy (XPS). The treated surfaces of the EPDM samples show a significant reduction in the contact angle measurement, indicating an increase in the surface energy. XPS analyses show the incorporation of polar nitrogen- and oxygen-containing groups on the rubber surface. After plasma treatment the presence of oxygen is observed due to surface oxidation which occurs when the samples are exposed to the air. Atomic force microscopy and scanning electron microscopy analyses indicate a decrease in the EPDM rubber surface roughness, promoted by surface etching during the plasma treatment. Strength tests indicate improvement of about 30% and 110% in the adhesion strength for the plasma treated EPDM/polyurethane liner interface and for the EPDM/epoxy adhesive interface, respectively. The adhesion strength of the EPDM/liner is similar to that obtained for the NBR/liner, which indicates that EPDM rubber can safely be used as thermal protection of the solid propellant rocket chamber.

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ResumoA vulcanização é um importante fator que determina as propriedades mecânicas da borracha, mas a influência do método de vulcanização nas propriedades mecânicas do material, ainda é um assunto pouco explorado na literatura. Neste artigo, uma formulação à base de poli-cis-isopreno ou borracha natural (NR), denominada NR4010-A, foi vulcanizada em prensa e autoclave, com o objetivo de avaliar a influência do método de vulcanização na formação das ligações cruzadas e, consequentemente, nas propriedades mecânicas do material. Amostras do material vulcanizado, pelos dois métodos, foram caracterizadas por meio de análise reométrica, ensaio de inchamento e testes mecânicos, onde foi avaliada a resistência ao rasgo e à tração. Os resultados mostraram que para essa formulação, nas mesmas condições de temperatura, o método de vulcanização por autoclave se mostrou mais eficiente em relação às propriedades estudadas. Palavras-chave: ligações cruzadas, NR, propriedades mecânicas, vulcanização. AbstractVulcanization is an important factor on rubber mechanical properties determination. The influence of vulcanization method on mechanical properties is still an ongoing issue. Thus, a composition based in natural rubber (NR), named NR4010-A, was vulcanized by autoclave and press, on purpose to evaluated the vulcanization method influence on crosslink formation and thereafter on the mechanical properties of this material. Samples of vulcanized material in both conditions were characterized through swelling, rheometer tests, tear strength, strain strength and hardness. The mechanical properties studied and crosslink density were increased when the material was vulcanized by autoclave. Therefore, autoclave vulcanization method showed be more effective than press at the same conditions of temperature.

Due to the excellent thermal and mechanical properties, the EPDM rubber is used as protective film in the aerospace industry. However, its chemical composition and structure do not allow good adhesive properties, making necessary a surface treatment to improve adhesion properties. Most of the conventional chemical methods make use pollutant solvents. Cold plasma is a clean technology that becomes an important alternative for treating these material surfaces. In this work we present a study of the EPDM rubber surface treatment by plasma. The process was conducted in a RIE plasma system excited by r.f. power using N2 and Ar gas mixtures. A significant improvement of the surface properties regarding to the adhesion properties was obtained. An optimization of the plasma parameters, such as gas ratio mixture, rf power, total gas pressure and treatment time is presented. The rubber surface properties were analyzed by goniometry and AFM. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

In the present work, a microwave excited plasma (2?45 GHz, 1 kW) was used to modify the surface characteristics of the ethylene propylene diene monomer rubber. The samples were treated with a mixture of nitrogen, hydrogen and argon plasmas. The operating gas pressure was in the 0?2-1 Torr range, the gas flowrate between 5 and 100 sccm and the treatment time varied from 10 to 600 s. The influence of the plasma treatment on the superficial characteristics of the samples was analysed by contact angle measurements and atomic force microscopy. The results show that the plasma treatment can promote an important decrease in the contact angle from 101u for untreated sample to 34u for samples treated in a mixture of H 2 /N 2 /Ar for 2 min, which corresponds an increase on the rubber surface adhesion work from 59 to 133 mJ m 22 .

Natural rubber (NR) is vulcanized with three different systems, using sulfur, peroxide and a mixed system consisting of peroxide and sulfur. The viscoelastic behavior of rubbers is evaluated by Dynamic Mechanical Analysis (DMA), using constant or multiple frequencies. From both DMA analysis methods, it is possible to verify that the rubbers vulcanized with sulfur or with the mixed system presented superior storage modulus in the rubbery region, and higher Tg values compared to the rubber vulcanized with dicumyl peroxide. These results indicate a higher degree of crosslinking for the NR containing sulfur in its vulcanization system. The master curves show that the rubber vulcanized with sulfur presented relaxation at a lower frequency due to the higher hardness, which is a consequence of the higher degree of crosslinking.