João Carlos Miguez Suarez

Sawdust reinforced polypropylene composites: a study of fracture behavior

Sawdust (20wt%) reinforced polypropylene composites were prepared with 22.4 wt% maleated polypropylene coated fibers. Tensile tests were performed at 400, 5 and 0.1 mm/min for composites and matrix. Scanning electron microscopy of these fracture surfaces together with the shape of the stress strain curves characterized ductile, brittle and ductile-to-brittle transition fracture modes. Processing conditions as well as the development of interfacial fiber/matrix adhesion are also discussed.

Tensile behavior of irradiated recycled polyolefin plastics

Solid wastes represent a potential source for raw materials in the world. In Brazil, municipal solid waste (MSW; 2-%) is expected to grow at a rate per year higher than the worldwide rate (1%). On the other hand, the consumption of polymer blends increases at a rate more than twice that of all plastics. Therefore, the recycling of polymeric blends has gained increasing attention in the world due to economic and environmental considerations. A two-step process, developed at the Institute (IMA/ UFRJ), allows one to recover plastic residues and permits the production of materials with controllable composition and homogeneous characteristics. The compression behavior of polyblends, composed of typical polymers that appear in domestic wastes-low and high polyethylenes-can be improved by gamma irradiation. In the present work, the tensile behavior of recycled 75/25 blends of low-density polyethylene (LDPE) and high-density polyethylene (HDPE), after exposure to gamma rays in the air, was investigated. Tensile testing, scanning electron microscopy, infrared and solid-state 13 C-nuclear magnetic resonance spectroscopy, as well as gel content were used to study the effect of gamma irradiation on the polymer blends. The tensile strength was found to increase with radiation dose while the elongation at break decreased. Our experimental results indicate that the gamma irradiation degradation process involves crosslinking at lower doses and chain scission at higher doses.

Comportamento térmico, mecânico e morfológico de compósitos de polietileno de alta densidade reciclado com fibra de piaçava

The use of natural fibers as reinforcement for thermoplastics, especially for recycled thermoplastics, has generated much interest due to their low cost, possibility of environmental protection and use of locally available renewable resources. In this work we evaluate the thermal, mechanical and morphological properties of composites of recycled high-density polyethylene (HDPE-r) with treated and untreated piassaba fibers (Leopoldinia piassaba) in different proportions (5, 10 and 15% w/w). The objective of this work is to obtain composites of HDPE-r / piassaba fiber in order to fulfill the needs of the consumer market, aiming at preparing low-cost plates for light duty jobs. Fibers were submitted to superficial treatment with silane in two different ways: direct incorporation and treatment with methanolic solution of the coupling agent. The results show that composites of HDPE with silane-treated-only fiber had better mechanical performance than methanolic solutions of silane; the increase on fiber - polymer matrix interface adhesion, as revealed from morphological analysis, can explain this higher performance. Thermal stability of the composites is not greatly affected with the addition of treated fiber.

Brittle–ductile transition of gamma-irradiated recycled polyethylenes blend

Abstract During the last few years interest in the development of new engineering materials from post-consumer polyolefins present in discarded commercial packaging has increased. These materials can be used as potential substitutes for products made from non-renewable, synthetic polymers. Our Institute has developed several such materials with good properties using plastic residues found in urban waste. One of these materials is a recycled 75/25 blend of outdoors, partially degraded low density polyethylene (LDPE) and high density polyethylene (HDPE). The exposure of this blend to low doses of 60 Co gamma -radiation improves its compression strength as a result of partial crosslinking. In this work the brittle–ductile transition temperature (BDTT) of this recycled blend was evaluated after exposure to gamma -radiation (100 and 500 kGy) in the presence of air. The experimental results show that the BDTT changes with the irradiation doses. The higher doses cause an increase in the Charpy impact values and a decrease in the BDTT. Gel permeation chromatography, mechanical tests and scanning electron microscopy were used to investigate these effects in the polymer material.

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.

Caracterização de artefatos elastoméricos obtidos por revulcanização de resíduo industrial de SBR (copolímero de butadieno e estireno)

The recycling of waste rubber has very important significances, such as protection of the environment and conservation of energy. Considering that most of published works concerning this subject are about tire recycling, the objective of this work was to develop and characterize formulations containing a type of industrial waste, from the manufacture of automotive profiles, based on styrene-butadiene rubber (SBR) for possible application in the industry. The compositions were formulated and characterized by thermal (differential scanning calorimetry), rheological (rubber processor analyzer), rheometrical (oscillatory disc rheomether), mechanical (tensile strength and tear resistance), chemical (cross-link density) and morphological properties (scanning electron microscopy). The results obtained for these compositions were compared to a control sample purchased for the industry, with the same formulation of the SBR scraps. Obtained results show that the revulcanization process was effective. Values for tensile strength and tear resistance were 70 and 50%, respectively, compared to values found for the control sample, indicating the possibility of using this residue as artifacts of lower technical requirement.

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.

Analysis of the fracture behavior of polypropylene: sawdust composites

Natural fiber reinforced composite is an emerging area in Polymer science. The use of lignocellulosic materials in thermoplastic composites may contribute to reduce the waste of vegetal biomass. The natural fibers are biodegradable, low cost materials having density and specific properties comparable to those of conventional fiber composites. In this work composites of polypropylene (PP) plus maleated polypropylene (MAPP) filled with sawdust were prepared under fixed processing conditions (mixing temperature, mixing time and rate of rotation). The composites were fractured by tension and the fracture mechanisms were characterized by scanning electron microscopy. The SEM studies of the fractured surfaces of the composites indicate that the failure is due to fiber pull-out accompanied by tearing of the matrix; the pull- out increases with MAPP content.

ESTUDO DO APORTE TÉRMICO DE SOLDAGEM NO COMPORTAMENTO BALÍSTICO DE UM AÇO DE ALTA DUREZA (HHA – HIGH HARDNESS ARMOR)

Resumo Foi estudado a influência do aporte térmico, de soldagem, sobre a resistência balística de um aço de alta dureza (HHA) temperado e revenido (HHA), utilizando o processo de soldagem a arco. O aço HHA, temperado e revenido, foi caracterizado por análise metalográfica, ensaios mecânicos e ensaios balísticos. Os resultados mostram que o aporte térmico da soldagem teve influência significativa nas propriedades mecânicas da Zona de Fusão (ZF) e da Zona Termicamante Afetada (ZTA), ocasionando mudanças na resistência balística. O melhor desempenho balístico do material soldado foi obtido para a soldagem de baixo aporte térmico. Palavras-chave:Blindagem de aço; Soldagem a arco elétrico com eletrodo revestido (SMAW); Zona de fusão (ZF); Zona termicamente afetada (ZTA).