Abstract
Polymeric composites based on natural rubber (NR) and plasticized starch (PS) obtained by peroxide cross-linking have been subjected to electron beam irradiation in order to investigate their degradation. The amount of PS ranged from 10 to 50 phr and the irradiation dose from 150 to 450 kGy. Irradiation was performed in atmospheric conditions using a linear electron accelerator of 5.5 MeV. Changes in chemical, physical, structural, and morphological properties of composites were correlated with variables, such as PS loading and irradiation dose. Thus, mechanical properties, gel fraction, cross-linking degree, water uptake, weight loss in toluene/water were compared with those obtained before irradiation. The changes in structure and morphology were studied by Fourier Transform Infrared Spectroscopy and Scanning Electron Microscopy. Both PS loading and irradiation dose were found to be responsible for the degradation installing. Moreover, it has been shown that at the dose of 450 kGy, chain scission is dominant over cross-linking.
Highlights
Huge and valuable sources of rubber are wasted in the absence of recycling
The goal of this paper is to study the degradation of elastomeric composites based on natural rubber (NR) and plasticized starch (PS) cross-linked with peroxide in the presence of Trimethylolpropane trimethacrylate (TMPT)
The increasing of p0/q0 ratio is associated with the prevalence of scission reaction against cross-linking, being well known the fact that p0 represents the degradation degree and q0 the cross-link density
Summary
Huge and valuable sources of rubber are wasted in the absence of recycling. After vulcanization in the presence of stabilizers and other additives, cross-links between the rubber chains are formed so that its natural degradation process is slow [1,2,3]. The three-dimensional cross-linked rubber network breaks down into lower molecular weight fragments, producing a physical recovery of rubber waste by using these fragments as a non-reinforcing filler [2]. The energy sources for polymer degradation can be thermal, mechanical, photochemical, biological, chemical, or from ionizing radiation, which excites active species such as free radicals, ions, and molecules and can significantly modify the molecular structure of the irradiated material. Ionizing irradiation of organic polymers induces molecular chain branching and cross-linking, which increase the molecular weight of the polymer, and chemical degradation or scission leading to breakage of the main chains of the macromolecule. The characteristics of electron beams favor the oxidation reactions that are responsible for the appearance and development of the degradation process in irradiated material [5]
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