Materials Science Forum Vol. 1012

Abstract: The use of natural polymeric materials has been growing notably in order to replace packaging from non-renewable sources. In this sense, cassava starch is a very promising natural polymer for this purpose due to its ease of production, the low cost, besides being biodegradable. However, cassava starch biofilms when dried have a brittle character requiring the addition of a plasticizer. Thus, biofilms were synthesized based on cassava starch (3%) with different percentages of glycerol (5%, 10%, 20%, 40% and 50%) to evaluate changes in physic-chemical and mechanical properties. The results indicate that the increase in percentage of glycerol contributed directly to the increase of water vapor permeability while decreases the contact angle and modulus of elasticity of cassava starch films.

Abstract: The objective of this work was to evaluate the influence of the order of sulfur addition on the mechanical properties of vulcanized natural rubber compounds. The addition of sulfur was carried out by two methodologies: (I) sulfur was added at the beginning of the mastication process, and (II) sulfur was added at the end of the mixing process. The compounds were obtained in open cylinder, and vulcanized in a press at 150°C. The vulcanization parameters were determined by rheometry, where as the mechanical properties were evaluated by testing samples for their tensile strength, tear strength, resilience, and Shore-A hardness. The dimensional stability of the vulcanized samples was also evaluated experimentally, by comparing specimens not heat-treated to those submitted to 100°C for 4 hours. Comparing the results of method (I) to method (II), the results, indicate that the addition of sulfur at the beginning of the mastication process (method I) yielded increases of 20 and 11% in tensile strength and tear strength, respectively, followed by a 9% increase in hardness, and 6% in resilience, without significant losses in maximum elongation. The dimensional stability test showed a reduction of 75% in the contraction for the vulcanized samples which had sulfur addition at the beginning of the mastication process of the unvulcanized NR rubber.

Abstract: Primary polymer recycling involves the reprocessing of defective parts and scraps in a processing line. The critical limitation for excessive use of primary recycling consists of the need to maintain the properties of the polymer above the required minimum level. The polymer degradation during the extrusion occurs by the combination thermal, oxidative and mechanical degradation. This work investigated the degradation of HDPE (High Density Polyethylene). Green HDPE (PV) and petrochemical HDPE (PN) were processed five times in a single-screw extruder and the flow rate, crystallinity and impact strength properties were evaluated. The increase in the number of reprocessing cycles increased the flow index and crystallinity values. The increase in the degree of crystallinity of the polymer, verified by the DSC analysis, evidenced the degradation of the material associated to the decrease of the size of the main chain (chain scission mechanism). The impact strength showed no significant change after five reprocessing cycles. Contrary variations were found in the crystallinity index considering the first and fifth processing, suggesting a change in the predominant mechanism of degradation.

Abstract: Polyethylene (PE) has an exclusive set of properties, such as good toughness and mechanical resistance as well as high flexibility, and ease conformation. However, when exposed to degrading agents, such as heat, humidity and radiation, macromolecular changes can be observed and consequently affect the PE. This work evaluated for the first time the thermomechanical and fracture behavior of low-density polyethylene (LDPE) subjected to degradation at different times of exposure to ultraviolet (UV) radiation. The changes induced in the chemical structure and the highlighted behavior were investigated through thermogravimetric analysis (TGA), differential scanning calorimetry (DSC), Fourier-transformed infrared spectroscopy (FTIR), reticulation content, tensile test, and scanning electron microscopy (SEM). The results suggest that UV radiation modify the failure of the polymer by reducing its crystallinity and dramatically increasing its degree of crosslinking. These modifications impair the LDPE mechanical performance as well as its thermal stability.

Abstract: Polysulfone/ Recam® composite membranes were prepared via the wet-phase inversion method. The interactions between polysulfone and additive were revealed by Fourier-transformed infrared spectroscopy and atomic force microscopy. Material properties, such as thermal and mechanical ones, were also analyzed. The increase of rugosity by augmenting the Recam® content was depicted by AFM images. Infrared spectroscopy provided very useful information about the interactions between polymer chains and additive. Thermal stability and mechanical resistance showed dependence on the additive content, which were higher for higher contents.

Abstract: In order to minimize impacts caused to environment and to save natural resources, especially from non-renewable sources, recycling of polymeric materials has been object of study. In this scenery, are included elastomeric materials, such as rubber, especially used in tires manufacturing, considering that pneumatic industry consumes around 60% of rubber production. Taking into account that final tires destination is a requirement based on norms and national and international laws, this work aims to the development of a study on the efficacy of micro-wave irradiation in the process of de-vulcanization of tire powder to be used in recycling. Tire powder was subjected to micro-wave irradiation and further merged to SBR (butadiene-styrene rubber) polymeric matrix, at 5, 15, 25 phr; after mixture, resulting compound was characterized for evaluation of physico-chemical and mechanical properties. For the assessment of all samples containing SBR and rubber powder there were applied following essays: Infra-red spectroscopy (FTIR), Tensile strength and elongation at break, Swelling Index. It was verified higher values for mechanical properties imparted by an increased quantity of rubber powder incorporated to SBR matrix.

Abstract: This work evaluates the mechanical and dynamic behavior of recycled polycarbonate (rPC) from industrial waste. This study aims to verify whether the recycled process adopted for polycarbonate promotes both mechanical and dynamic properties values under compressive stress, similar to those found for virgin polycarbonate. The mechanical recycling of the rPC was carried out using the thermoforming technique in a thermal press. Two tests were carried out to evaluate the dynamic response of rPC. The quasi-static compression test was performed on a universal machine. The dynamic in a split Hopkinson pressure bar was performed with three different strain rates. The results showed that the mechanical and primary recycling adopted in this work promoted values of yield stress in compression (77 MPa) and dynamic (up to 118 MPa), close to or superior to those reported so far in the literature.

Abstract: This work investigates the mechanical behavior of a PCLIGHT type of polycarbonate (PC). PC samples display interesting results after thermal degradation at different temperatures. Samples of PC in sheet form were exposed for a period of 5 hours at temperatures of 50, 100, 150 e 200°C. After, thermogravimetric test, flexural, impact and tensile tests were performed. The results show that the samples treated at 200oC has their mechanical performance affected this indicates that the temperature acts on the PC embrittlement behavior. Thus, it can be inferred that temperatures above 150oC can negatively influence the mechanical behavior of the polycarbonate indicating that this material should not be used in association with high temperatures.

Abstract: The increasing use of poly methyl methacrylate (PMMA), often replacing tempered glass, is a consequence of its high rigidity, practicality, lightness and transparency. However, current manufacturing standards in the polymer industry recommend specific tests on these materials. The present study aims to mechanically test the properties of poly methyl methacrylate (PMMA) material under conditions that simulate a much more aggressive environment than usual. Infrared spectroscopy (FTIR), thermogravimetric (TG/DTG) tests, Izod impact tests, and scanning electron microscopy (SEM) analysis were performed. The results showed that poly (methyl methacrylate) (PMMA) maintained its tensile mechanical properties up to 105°C. Regarding the impact tenacity, the temperature negatively influenced the performance of this polymer.

Abstract: The effects of the separator thickness (δ) upon the equivalent series resistances (ESR) and specific capacitances (C_s) of supercapacitors electrodes have been investigated using commercially available porous filter paper (δ=150 μm, pores size=7.5 μm, 80 gm^-2). Commercial activated carbon electrodes immersed in 1molL^-1 KOH electrolyte (25°C) have been employed in this study. The specific capacitances were calculated from cyclic voltammetry curves at room temperature employing various scan rates (5, 10, 15 and 30 mVs^-1). Internal series resistances of the supercapacitors were measured using the galvanostatic charge discharge curves also at room temperature. A maximum of 28 separators (δ=4200 μm) have been employed in this investigation. It has been shown that the ESR increases substantially with separator thickness (from 3.1 to 7.9 Ωcm²). The specific capacitance decreased somewhat with increasing separator thickness and scan rates (from 64 to 52 Fg^-1; at 5 mVs^-1). The microstructures of the electrode material have been investigated using scanning electron microscopy (SEM) and chemical microanalyses employing energy dispersive X-ray analysis (EDX). A compositional and morphological evaluation of these electrodes showed a very homogeneous microstructure.