Mihaela Nituica

This paper describes the development of new types of dynamically cross-linked thermoplastic elastomers based on ethylene-propylene-terpolymer rubber and low-density polyethylene, reinforced with plasticized starch and montmorillonite with a chemically modified surface. An octylphenol-formaldehyde resin in the presence of stannous chloride dihydrate was used as a vulcanizing agent. The samples were obtained on a Brabender Plasti-Corder mixer, at appropriate temperatures and rotation speeds, using the dynamic vulcanization method and the melt intercalation technique. The mixtures obtained were modeled in the form of plates with standard dimensions using specific molds and a laboratory-scale electrical press. The obtained samples were analyzed from the point of view of the physical-mechanical properties, the melt flow index, as well as from the structural and morphological point of view. It was observed that the characteristics of the samples are influenced by both the composition and the methods of obtaining used. According to the obtained characteristics, the new elasto-plastic materials can be used in fields such as the footwear industry (for the production of: soles, heels, protective boots), in the rubber and plastics industry, the automobile industry, agriculture or construction (when making gaskets, technical items, hoses, etc.). They can be easily processed into different finished products by methods specific to plastics.

EPDM/hemp fiber composites with fiber loading of 0–20 phr were prepared by the blending technique on a laboratory electrically heated roller mill. Test specimens were obtained by vulcanization using a laboratory hydraulic press. The elastomer crosslinking and the chemical modification of the hemp fiber surface were achieved by a radical reaction mechanism initiated by di(tert-butylperoxyisopropyl)benzene. The influence of the fiber loading on the mechanical properties, gel fraction, swelling ratio and crosslink degree was investigated. The gel fraction, crosslink density and rubber–hemp fiber interaction were evaluated based on equilibrium solvent-swelling measurements using the Flory–Rehner relation and Kraus and Lorenz–Park equations. The morphology of the EPDM/hemp fiber composites was analyzed by scanning electron microscopy. The water absorption increases as the hemp fiber loading increases.

The paper presents the obtaining of new green polymeric composites using a sustainable reactive processing method, namely electron beam irradiation. EPDM rubber mixtures were reinforced with different amounts of short hemp fibers, which were then irradiated at doses between 75 and 600 kGy. The samples were analyzed by determination of physical–mechanical properties, sol–gel analysis, crosslink density (using the well-known modified Flory–Rehner equation for tetra functional networks), determination of rubber–fiber interactions (using the Kraus equation), water uptake test and FTIR analysis. The obtained results indicate an improvement of the hardness, the tensile and tear strength as the quantity of hemp fibers increases. As the irradiation dose increases, there is an increase in the degree of crosslinking and the gel fraction. Analyzing the behavior of the irradiation samples using the Charlesby–Pinner equation, it is observed that all the samples tend to crosslink by irradiation, the share of degradation reactions being low. For these reasons, the new materials can be used in the food, pharmaceutical or medical field, because the obtained products are sterile and can be easily resterilized by irradiation. They have high elasticity values and can be used to make packaging, seals and other consumer goods.