Agnes F. Martins

Mechanical and fractographic behavior of natural rubber-cellulose II composites

Composites of natural rubber (NR) and cellulose II (Cel II) were prepared by co-coagulation of natural latex and cellulose xanthate mixtures. The influence of increasing amounts of Cel II, varying from 0 to 30 phr, on the mechanical properties was investigated. The topography of the fracture surfaces of tensile, tear and abrasion specimens after testing was observed by scanning electron microscopy (SEM). The fracture surface morphology was correlated with the mechanical properties. As the cellulose II content increases, the materials showed a gradual change in the mechanical properties and in the fracture mechanisms. The composite with 15 phr of Cel II was found to give the best tensile and tear performances. The failure surfaces and the fracture mechanisms of unfilled and filled natural rubber composites depended on the nature of the test-tensile, tear or abrasion. The SEM evaluation of the tensile fracture surfaces was the best observation method to show the effect of cellulose II on the elastomeric matrix.

Produtos poliolefínicos reciclados com desempenho superior aos materiais virgens correspondentes

The balance of crosslinking and scission reactions in polyolefin chains when exposed to free-radical, environmental conditions may result in good properties and new applications. Discarded, post-consumer high quality materials are more and more attractive for recycling. The plastic residues from food packages and large dimension automobile residues, as car bumpers, are good examples of those materials. In the present work, we report mechanical properties of IMAWOOD®, plastic lumber from urban solid waste, mostly PE packaging residues, and IMACAR, from discarded car bumpers, mainly PP/EPDM blends. IMAWOOD® showed improved mechanical behavior after gamma-irradiation. IMACAR® was highly resistant to impact.

Influência da mica nas propriedades mecânicas e dinâmico-mecânicas de composições de borracha natural

In this work the influence of mica on the mechanical and dynamic mechanical properties of vulcanized natural rubber compositions was studied. The crosslinking density of the compositions was also determined. The data were compared to those of the unfilled composition. The results indicate an increase in modulus, hardness, crosslinking density and compression set as well as a decrease in resilience and abrasion resistance for the natural rubber compositions with increasing mica contents. The best performance for tear strength and stress at break was achieved with 30 phr of mica. The dynamic mechanical behavior of the compositions (DMTA) is in agreement with their mechanical properties.

Efeito do envelhecimento nas propriedades mecânicas e dinâmico-mecânicas de composições de borracha natural com mica

The effects from ageing of materials is important in terms of cost and quality, particularly if the products are to be used under severe weather conditions. In this work, the effect of accelerated ageing in vulcanizable compositions of natural rubber and mica was studied. The amount of the mineral filler employed varied from 0 to 40 phr. The mechanical and dynamic-mechanical properties of different compositions were evaluated as well as crosslink density, before and after ageing, and the results were compared to those obtained for the unfilled composition. It was found that, either before or after ageing, the amount of mica must not exceed 30 phr. It was also concluded that mica is responsible for the protection of natural rubber composites from ageing under the selected conditions. The dynamic mechanical properties obtained from DMTA analysis corroborate the mechanical properties evaluated.

Compósitos de borracha natural ou policloropreno e celulose II: influência do tamanho de partícula

The aim of this work was to develop light composites with properties of technological interest by using elastomers of different polarities. This was achieved by employing cellulose II, in the powder form, as filler in natural rubber (NR) and chloroprene (CR). Cellulose II was obtained by coagulation of cellulose xanthate solution, in acid medium, under stirring and at room temperature, which represents, to our knowledge, a new way of obtaining this type of filler. Composites with 10phr of cellulose II and NR or CR were prepared having the particle size as variable. The mechanical properties and the microscopic aspect of the different composites were evaluated and compared with compounds without filler. The results indicated best results for the CR composite, influenced by the polarity of the elastomeric matrix and by the particle size, as a consequence of the milling conditions of the filler used.

Recycled car bumpers' impact resistance investigated by wide‐angle X‐ray diffraction

The recycled polyolefinic product from discarded standard car bumpers collected from Rio de Janeiro suburb shops was characterized by mechanical and wide-angle X-ray scattering (WAXS) methods. We found that the recycled plastic mixture is composed mainly of polypropylene (PP), containing ethylene-propylene-diene (EPDM) terpolymers and a minor proportion of high-density polyethylene (HDPE), and is highly resistant to impact. The results were compared with the corresponding data obtained from binary and ternary blends of virgin PP, EPDM, and HDPE.

Misturas NR/SBR: modos de preparação e propriedades

Frequently a set of properties required for a given application cannot be accomplished by only one elastomer and, thus, mixtures of two or more polymers must be employed. In these cases, the other ingredients normally added are dispersed differently, depending on their affinity to each polymer. The degree of dispersion each additive experiences in each elastomeric phase will influence the rate and the degree of vulcanization and will certainly have consequences on the performance of the final product. In this work, natural rubber (NR) was mixed to butadiene-styrene elastomer (SBR) in a 50:50 w/w ratio. The compositions were prepared in a two-roll mill, according to ASTM D3182, introducing the additives in four different modes. After vulcanization, the mixes were investigated as for their mechanical (stress and tear strengths and hardness), dynamic mechanical thermal and morphological analysis. Mechanical properties were evaluated according to ASTM procedures, specific for each test. The results show that, although having been prepared following the same formulation, the properties of these mixtures are influenced by the preparation mode, which could be detected by mechanical and morphological analysis and evidenced through more sensitive methods as DMTA. For NR/SBR blends, the best properties are achieved when one favours the vulcanization of the rubber with inferior properties, that is, SBR.

The Influence of Degraded, Recycled PP on Incompatible Blends

Publisher Summary This chapter discusses the influence of degraded, recycled PP on incompatible blends. The recycling of post-consumer polyolefins has attracted much interest because these resins—low density polyethylene (LDPE), high density polyethylene (HDPE) and polypropylene (PP)—are some of the most common polymers in the domestic plastic waste stream. Recycled plastic can be obtained by two different approaches: a two-step process, involving plastics fractionation and processing of the separated plastics fractions; and a single-step process, using directly the mixture of plastic residues. Reprocessing mixed polyolefin waste can lead to products with lowered mechanical properties, because these polymer mixtures are usually incompatible. This chapter investigates the compatibilizing action of molecularly modified, recycled PP on the mechanical properties of 50/50 PP/HDPE blend, as suggested by preliminary experiments carried out in the laboratory. Moreover the experimental results suggest that the degradation that occurred in PP molded, post-consumer artifacts after exposition to natural, uncontrolled outdoor conditions provided spontaneous, non-oxidative chemical modifications on PP molecules that brought a certain degree of compatibilization action toward polyolefin residues.