Maria Zanin

Consecutive steps of PET recycling by injection: evaluation of the procedure and of the mechanical properties

The procedure of five consecutive recycling steps by injection moulding of postconsumer PET was evaluated on the basis of processing and drying parameters. The equations that govern the increase in sample mass of the polymer while in contact with the atmosphere were obtained on the basis of weight variation measurements before and after drying. Two series of consecutive recycling steps were also carried out, starting from virgin material (with and without sieving), which showed that, for the sieved material, the decrease in productivity was always in the same order of magnitude as the decrease in viscosity. Thus, the remaining differences, which exceeded 400%, can be attributed to the presence of powder. The crystallinity, transition temperatures, concentration of carboxyl end-groups, tensile properties, and impact resistance of the samples obtained in each step were determined. The number of carboxyl end groups increased by about three times after the five recycling steps and the crystallinity was enhanced, going from 23% to 37%, which explains the alterations in the modulus of elasticity, elongation at break, and impact resistance.

Influência de Meios Reacionais na Hidrólise de PET Pós-Consumo

The depolymerization of polyethylene terephthalate - PET in pure water and in 7,5M aqueous solutions of acetic acid, sulfuric acid, sodium acetate and sodium hydroxide was tested at 100oC and 1 atm, in order to obtain terephthalic acid (TPA). The effect from the size of the particles on the reaction kinetics was studied quantitatively. Pure water and the solutions of acetic acid and sodium acetate practically did not degrade PET after five days of reaction, while the sulfuric acid solution allowed 80% of depolymerization during the same period. Sodium hydroxide was the best hydrolysis agent, resulting in 95% depolymerization of the the larger particle size PET (between 2mm and 1,19mm) in 7 hours and 98% of the smaller particle size PET (less than 1,19mm) in 5 hours. Terephthalic acid was obtained, purified and characterized, and the results were similar to those of petrochemical TPA (purity higher than 99%).

Post consumer pet depolymerization by acid hydrolysis

The reaction of post-consumer poly(ethylene terephthalate) with aqueous solutions of sulfuric acid 7.5 M was investigated in terms of temperature, time and particle size. The reaction extent reached 80% in four days at 100°C and 90% in 5 hours at 135°C. TPA obtained was purified and considered in the same level of quality of the commercial one after tests of elemental analysis, particle size and color. It was concluded that the hydrolysis occurred preferentially at the chain ends and superficially, having as controller mechanism the acid diffusion into the polymer structure. The shrinking-core model can explain the reaction kinetics.

Avaliação das propriedades reológicas de blendas de PEAD virgem/PEAD reciclado

Neste trabalho, as propriedades reologicas de blendas de PEAD virgem e PEAD reciclado, em diferentes porcentagens, foram avaliadas em regime permanente, transiente e dinâmico de cisalhamento utilizando-se reometria cone-placa e reometria capilar. Embalagens de PEAD pos-consumo foram coletadas e submetidas aos processos basicos de recuperacao de plasticos: lavagem, moagem e secagem. Formulacoes, previamente estabilizadas, contendo 0, 25, 50, 75 e 100% de material reciclado, adicionado a resina virgem, foram reprocessadas por extrusao e posterior injecao. Das medidas das propriedades reologicas foi possivel concluir que a incorporacao de material reciclado proveniente de residuo pos-consumo a resina virgem promove, neste caso, uma diminuicao da massa molar e aumento na sua distribuicao. Alem disso, um estudo das propriedades reologicas permite a predicao de seu comportamento frente ao processamento de resinas recicladas pos-consumo.

Optimization of neutral hydrolysis reaction of post-consumer PET for chemical recycling

The neutral hydrolysis reaction of post-consumer poly(ethylene terephthalate) in solid state was studied through the reaction of the polymer with water at the molar ratio 1:91 with autogenous pressure. Two sizes of post-consumer PET flakes and temperatures of 135°C, 170°C and 205°C with pressures of 4.0 atm, 7.5 atm and 13.5 atm, respectively, were considered. With reaction time equal to 6h, the method reached 99% depolymerization at 205°C, 8.2% at 170°C and 1.7% at 135°C. The reaction extension was measured by separating the terephthalic acid formed in the process and calculating by gravimetry how much material could still be reacted. Through the viscosimetry of diluted solutions and the counting of carboxylic end groups in the remaining material from the gravimetric assay, it was possible to suggest that the reaction occurs randomly and in the whole volume of the polymeric particle and not solely on the surface. The terephthalic acid obtained and then purified was characterized by elemental analysis, magnetic nuclear resonance, size and particle size distribution and spectrophotometry in the visible spectrum, and it was similar to the petrochemical equivalent, with purity recorded in carbon base equal to 99.9%.

Reciclagem de PET advindo de garrafas de refrigerante pós-consumo

A reciclagem de PET pos-consumo foi investigada a partir de cinco ciclos sucessivos de moldagem por injecao. Amostras obtidas em cada passo foram submetidas a ensaios para determinar a cristalinidade, degradacao, produtividade, fluidez e propriedades mecânicas. Os resultados indicam que a garrafa e reciclavel em termos de processamento, principalmente nos quatro primeiros passos. O numero de grupos terminais carboxilicos aumentou cerca de 300% da primeira ate a quinta reciclagem, indicando quebra de cadeias. Esta degradacao e o aumento da cristalinidade (de 11% para a garrafa moida para 25% na quinta reciclagem) explicaram as alteracoes nas propriedades mecânicas.

Caracterização do efluente de lavagem de filmes plásticos pós-consumo e determinação das propriedades reológicas do material reciclado

Uncleaned plastic films constitute about 20% by mass and 8% by volume of Urban Solid Waste (USW). These amounts are worrying, because just 10% of all collected waste has a controlled final destination, in Brazil. One aggravanting problem in plastic film recycling is the effluent from washing, which can be very contaminated. The objectives of this study were: to develop procedures to clean the plastic films from USW; to characterize some washing effluents of these films; to reprocess HDPE and LDPE films separately with an antioxidant additive (together with a flow additive) and to determine the rheological properties of the recycled material. The experimental results showed that the washing water agitation time had a more important role in cleaning the plastic than the percentage of NaOH used in the washing step. Secondly, the effluent from wasu\ing was shown to carry quantity of organic material (BOD - 700 mg/l) and high turbidity. Lastly, the recycled material was perceptlibly altered only after the third reprocessing (extrusion).

Marx como referencial para análise de relações entre ciência, tecnologia e sociedade?: evitando equívocos e ampliando possibilidades na aplicação de conceitos marxianos da teoria do mais-valor no campo CTS

EnglishIn contemporary capitalism, in which the productive application of science, techniques and technology has a determinant role, it is necessary to search for reference models that are capable of explaining its subjacent processes, as well as the broader social effects. In this sense, this paper aims at critically analyzing the entitled paper Marx como referencial para analise de relacoes entre ciencia, tecnologia e sociedade, indicating aspects, due to its attempt to appropriate the Marxian concepts of the theory of surplus value for the critical comprehension of STS relations. From a conceptual confusion, basically founded on a deficient distinction among duration, intensity and productivity of labor, the concepts of the absolute and relative surplus diverge from the original Marxian definitions. Because of this and for centralizing its analysis in the reduction of workforce value, the complexity of the capitalist relations and social development due to the scientific and technological changes are put aside. portuguesNo capitalismo contemporâneo, em que a aplicacao produtiva da ciencia, da tecnica e da tecnologia assume um papel determinante, faz-se necessario buscar modelos de referencia capazes de explicar os processos subjacentes a mesma, bem como os efeitos sociais mais amplos. Neste sentido, este artigo objetiva analisar criticamente o artigo intitulado Marx como referencial para analise de relacoes entre ciencia, tecnologia e sociedade, apontando aspectos, face a sua tentativa de se apropriar dos conceitos marxianos da teoria do mais-valor para a compreensao critica das relacoes CTS. A partir de uma confusao conceitual, fundada basicamente numa distincao deficiente entre duracao, intensidade e produtividade do trabalho, os conceitos de mais-valor absoluto e relativo divergem das definicoes marxianas originais. Por isto e por centrar a analise na reducao do valor da forca de trabalho, a complexidade das relacoes capitalistas e o desenvolvimento social em funcao das mudancas cientifico-tecnologicas sao deixados de lado.

Influência de aditivos na rigidez dielétrica do polietileno de alta densidade

Neste trabalho sao apresentados resultados de ensaios de ruptura dieletrica de curta duracao com rampa de tensao positiva em amostras de polietileno de alta densidade (HDPE), modificadas com diferentes niveis de aditivos (dioxido de titânio, negro de fumo, antioxidante e estabilizante a ultravioleta). Esses resultados foram analisados estatisticamente pela distribuicao de Weibull. Os parâmetros desta distribuicao (β e Eγ) foram determinados pelos metodos Grafico e de Maxima Verossimilhanca. Pode-se concluir que os aglomerados de negro de fumo sao prejudiciais a rigidez dieletrica e que o parâmetro de forma β desta distribuicao pode ser empregado para avaliar as condicoes de mistura dos componentes na formulacao, as quais afetam a rigidez dieletrica. Por meio de microscopia otica pode-se verificar que o parâmetro β, quando determinado pelo metodo Grafico, representa melhor a dispersao dos referidos aditivos na matriz polimerica.

Caracterização elétrica e física de compósitos de copolímero EPDM vulcanizado e trihidróxido de alumínio

In this work, electrical and physical properties of vulcanized copolymer EPDM-ENB reinforced with alumina trihydrate, ATH, were investigated. Characteristics of the vulcanizating process, tear resistence, tensile strenght at break are given for different contents of ATH. The dependence of the electric conduction on the applied voltage were measured for the composites. A linear dependence of the logarithm of electric conductivity on the square root of the applied electric field was found. Such results were discussed employing Poole-Frenkel and Schottky theoretical models.