POLYOLEFINS | MATERIALS


a PP matrix and/or to reduce costs,” said the researchers, most of whom are from the Troyes University of Technology (UTT) in France. “Rein- forcements, which are much stiffer and stronger than the polymer, generally improve its modulus and strength. Consequently, the modification of mechanical properties can be regarded as their main function.” In the study, three grades of talc-filled PP – and


one of glass fibre-filled PP – were tested and characterised for use as a middle layer in a three- layer sewage pipe. The results showed increases of 100% and 250% in tensile and flexural modulus through the use of 30-50wt% talc-filled PP and 30wt% glass fibre-filled PP, respectively. This high increase in rigidity would allow the manufacture of pipes with higher ring stiffness, said the researchers. Composites filled with 30wt% talc or glass fibre showed good filler-matrix interaction and good filler distribution and dispersion. However, reduced filler-matrix interaction was seen in the composite filled with 50wt% talc. The research was published in the Journal of Applied Polymer Science.


Pipe vision At the same time, researchers in China have identified and classified defects in PE gas pipelines using a neural network image recognition system. “Traditionally, automatic classification of images is carried out using extracted image features, which are used to represent unclear information in the original pixel values,” said the researchers, in a paper published in Applied Sciences. “Convolu- tional neural networks (CNN) have taken the place of that approach in recent years.” The researchers, from Xinjiang University and


elsewhere, began by performing preliminary screening of acquired images. Images of defective PE gas pipelines were pre-processed. Then, edge detection of the defective images was performed using an improved version of the Sobel algorithm. Finally, the defect images were morphologically processed to obtain binary images. These binary images were processed using a neural network model called VGG16 – to helped to ‘train’ the classifier to recognise defects. Part of the approach was to convert the colour images to ‘grayscale’ – which helps to characterise the brightness and darkness of an image. It also uses less memory and enable faster computing, compared to colour images. “For the defective PE gas pipeline images,


contrast was enhanced using gamma transform, and noise was removed using the dual filtering method.”


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Right: Rehau is using Bornewa- bles polypro- pylene to make furniture edgebands


Pipe ageing Also in China, researchers have assessed the degradation and characterisation methods used on PE gas pipes after natural and accelerated ageing. “Solving the divergence between natural and


accelerated ageing behaviour is the core for the lifetime prediction of polymeric materials,” said the researchers from Beijing Jiaotong University. In a paper published in Polymer Degradation


and Stability, the degradation of PE pipes was evaluated by accelerated tests with exposure time up to 10,000 hours. At the same time, the ageing behaviour was also evaluated for PE pipes in operation after long-term service. To characterise the effect of thermo-oxidative


ageing, methods including tensile testing, scanning electron microscopy, differential scanning calorim- etry, infrared spectroscopy and a new technique – nano-indentation – were performed. The results showed that degradation of PE pipes under oxidative conditions has time-dependent properties and spatially heterogeneous oxidation profiles. “The current engineering-based prediction of PE pipe failure or lifetime lacks consideration of diffu- sion-limited oxidation and in-depth discussion of degradation mechanism,” said the researchers. “This indicates it is too early to estimate the lifetime or the remaining lifetime of the PE pipes in operation.”


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March/April 2023 | PIPE & PROFILE EXTRUSION 17


IMAGE: BOREALIS


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