Effect of weathering conditions on the degradation behaviour of ABS

Fundação para a Ciência e a Tecnologia (FCT) - Bolsa de Doutoramento SFRH/BDE/15657/2007Poliversal – Plásticos e Tecnologia, S.A

Optimisation of rotational moulding of polyethylene by predicting antioxidant consumption

Rotational moulding is used to manufacture hollow plastic products. The process offers many advantages to the designer, but it is hampered by a strong dependence on trial and error methods to achieve good part quality at economic production rates. During rotational moulding, the polymer is subjected to relatively high temperatures for long periods of time in the presence of air. This can lead to degradation of the polymer at the inner free surface of the moulded article, with consequent deterioration of the mechanical properties of the part. The processing conditions that lead to degradation vary with factors that affect the heating rate, such as the type of mould used. In this work a method is proposed to predict the onset of degradation, on the basis that this occurs when the concentration of anti-antioxidant in the polymer reaches zero. Good agreement between the experimental and predicted optimum processing temperature was obtained for two grades of polyethylene stabilised with two different antioxidant systems. Using the method described, it is now possible to identify the best rotational moulding conditions for a particular polymer so that more efficient cost-effective parts can be produced

Natural and accelerated weathering of Acrylonitrile-Butadiene-Styrene (ABS)

Spectroscopic methods, UV/Vis and Fourier Transform Infrared with an attenuated total reflectance (ATR) accessory, were applied to evaluate the influence of light stabilizers on ABS samples exposed to accelerated and natural weathering conditions up to 600h and 360 days, respectively. Some important differences in the formation rate of carbonyl compounds were found when comparing accelerated to natural weathering exposure. While stabilized samples exposed to accelerated weathering reveals slower formation of carbonyl groups than unstabilized ABS, the carbonyl absorption of samples exposed to natural weathering is comparable to the unstabilized ones. The behaviour of light stabilizers during natural exposure is somewhat surprising and cannot be only associated to its stabilizing effect. The disappearance of light stabilizers only after one month of exposure could be due to molecular scission of light stabilizers with consequence volatilization and diffusion of these fragments on the surface, while under acceleration conditions seems to occur by photochemical reactions. The results obtained are interesting showing that sometimes the material behavior under real weathering conditions cannot be predicted from the results of accelerated laboratory experiments.Fundação para a Ciência e a Tecnologia (FCT) - SFRD/BD/48512/200

Optimization of the rotational moulding process for polyolefins

Hollow plastic parts can be made by a number of manufacturing methods, but only rotational moulding offers the ability to create one-piece, stress-free parts with attractive economics. However, the fundamental nature of rotational moulding is such that cycle times are long. Consequently, the plastic is subjected to relatively high temperatures, in the presence of air, for excessive periods of time. This can lead to thermal and oxidative degradation at the inner free surface of the plastic, resulting in a deterioration in the performance of the moulded part. The industry relies heavily on the experience of operators to establish the best processing conditions to avoid degradation, but this is problematic and inefficient. Unfortunately, automatic process control is difficult owing to the complex rotation of the mould. Recent developments highlighting the importance of the peak air temperature inside the mould have been an important step forward, but ever-increasing technical demands on moulders make it clear that more sophisticated process control is needed. It is known that the processing conditions that lead to degradation vary with factors that affect the heating rate, such as the type of mould used and the thickness of the end-product. In the work reported here, a method is proposed for predicting the onset of degradation, on the basis that this occurs when the concentration of antioxidant in the polymer reaches zero. Good agreement has been obtained between the experimental and predicted optimum processing temperature for polyethylenes stabilized with different antioxidant systems. A procedure is described for identifying the best rotational moulding conditions so that more efficient manufacturing methods can be achieved

Development of instrumented equipment for research in rotomoulding: a study on dimensional stability

Nos últimos anos, tem-se assistido ao aumento da utilização da Moldação Rotacional para o fabrico de produtos com elevados requisitos de qualidade. A produção deste tipo de artigos exige um controlo apertado do processo e a extrapolação das propriedades do produto a partir das variáveis de processamento. Neste trabalho, descreve-se um equipamento protótipo à escala laboratorial desenvolvido para a produção de produtos rotomoldados de pequena dimensão sob condições de fabrico controladas e monitorizáveis. O equipamento tem característi cas de tipo rock and roll e de tipo vaivém, com um forno elétrico O sistema de monitorização incorpora um inovador sistema de aquisição e transissão de dados da temperatura no interior do molde constituído por um emissor de rádio que opera no exterior das câmaras de aquecimento e arrefecimente. O equipamento pode operar em ciclo automático ou em ciclo semiautomático com o operador a controlar o tempo de aquecimento. Descreve-se ainda um estudo experimental realizado com o equipamento, sobre o efeito das condições de processamento na deformação de caixas rotomoldadas em polietileno. Os resultados mostram que a configuração do suporte do molde pode ter um efeito importante nos desvios dimensionais das peças rotomoldadas.Rotational moulding is being increasingly used for the production of quality products. Theses require a tighter control of the process and also the inference of the properties from the processing set up. Prototype equipment at laboratory scale was developed to rotomould small size products under controlled and monitorable processing conditions. This equipment is of the rock and roll type with an electric oven. The monitoring system incorporates a novel data acquisition and transmitting system for the temperature inside the mould that features a radio emitter that operates outside the heating and cooling stations. The equipment can work in automatic cycling or semi-automatic cycling with operator control of the heating time. An experimental study on the effect of processing conditions on the deformation of polyethylene boxes is described. The results show that the configuration of the mould support system can have an important effect on the dimensional deviation of rotomoulded parts