Separation and recovery of ABS from blended with high impact polystyrene (HIPS)

ABSTRACT

This article illustrates the effort by our laboratory to develop a froth flotation process for separating and recovering plastics from blended plastics ABS and HIPS. A process for recovering and separating ABS from HIPS was developed. The resulting ABS product was analyzed and its physical and mechanical properties were established. Its properties resembled those of virgin ABS extrusion grade that is commercially sold today and widely used by manufacturing cabinet of fridge. Injection-molding tests were also conducted by molding machine Haitian 1600. Molded part showed that the recovered ABS met the specification for this application. These results confirmed that the recovered ABS can be used as a substitute for virgin plastic materials for molding parts for other durable goods.

АННОТАЦИЯ

Эта статья иллюстрирует усилия нашей лаборатории по разработке процесса пенной флотации для отделения и извлечения пластмасс из смешанных пластмасс ABS и HIPS. Был разработан процесс восстановления и отделения ABS от HIPS. Полученный продукт из АБС был проанализирован и установлены его физико-механические свойства. Его свойства напоминали свойства первичного экструдированного АБС-пластика, который сегодня продается в коммерческих целях и широко используется при производстве холодильных шкафов. Тесты литья под давлением также проводились на формовочной машине Haitian 1600. Формованная деталь показала, что восстановленный АБС соответствует спецификации для данного применения. Эти результаты подтвердили, что регенерированный АБС-пластик можно использовать в качестве заменителя первичного пластика для формования деталей для других товаров длительного пользования.

Keywords: ABS- Acrylonitrile-butadiene-styrene, HIPS- High impact polystyrene.

Ключевые слова: ABS - Акрилонитрил-бутадиен-стирол, HIPS - ударопрочный полистирол.

Introduction

Plastics have become an integral part of our lives. Plastics are an excellent and very useful material and they are functional, hygienic, light, and economical. Using a key polymer processing system, plastics produce diverse products used in packaging, automotive and industrial applications, and also extensively used in medical delivery systems, artificial implants and other healthcare applications, water desalination, and removal of bacteria, etc.

Until the 1930s and in early 1940s, thermoplastics were not common material. Ever since the first industrial scale production of plastics (synthetic polymers) took place in the 1940s, the production and consumption has increased considerably. Although plastic materials are relatively new, they have become basic and indispensable in our life with different shapes, sizes, and applications that can be seen daily at home, office, and even on the street. (1) Constant advances in high-tech products lead to an increment in electrical and electronic devices consumption, meaning that most of the replaced equipment are turned into scrap (2). The stream of waste from electrical and electronic equipment contains several valuable and recyclable materials like gold, silver, platinum, palladium, plastics and silica (3; 4). While plastics are neither the main nor the most abundant, they occupy a lot of space in landfills because of their high volume due to low density and parts shape (5; 6). Plastic from electronic equipment represents approximately 18 wt% of this waste stream consisting mainly of thermoplastics that can be recycled by reprocessing (7). For their recycling, they are generally chopped, washed and sorted by type involving relatively high costs (8). Plastic resins from waste electronic equipment are similar which makes it very difficult to separate them by type using automatic sorting methods. There are several specific automatic techniques but their precision highly depends on plastic stream composition (9). Near infrared spectroscopy (NIR) is the best known automatic method for plastic separation by type. However, its use for plastic WEEE classification is not optimum because these materials usually are dark colored making it difficult to classify by NIR. Also, the major amount of plastic WEEE contains styrenic resins with very similar molecular structures (like ABS and HIPS) and consequently, they are not well differentiated by NIR (Arends et al., 2015; Maris et al., 2015; WRAP, 2009). Also, the last problem strongly affects sorting by other techniques like density separation and impact milling (WRAP, 2009; Tall, 2000). The separation of different plastics or groups of plastic types based upon their different densities is probably the most cost-effective, high-capacity process in automated industrial separations for recycling plastic waste. Such separations are comparatively simple, easily automated and flexible in operation. On the basis of weight of material treated industrially, it is globally the most widely used materials separation process. In a few instances density separation is a well-established method for producing finished plastic separations in situations in which there is a definite difference in density of the product in comparison with all other materials present. Such separations are based on a float/sink process in which particles of different densities are placed within a medium of intermediate density. Lower density particles float whereas those of higher density sink at rates corresponding to their relative buoyancy in the medium under the force of gravity. However, materials that have similar densities, such as ABS acrylonitrile butadiene styrene, HIPS, difficult to separate in high purities by this simple and in expensive technique.

ABS and HIPS most dominated regarding to using them in production of refrigerators sheets, if they contaminated each other would sever degrade of their properties, specifically their tensile and impact strength because the two plastics are not compatible. Present article is providing an improved method process for separation of acrylonitrile butadiene (ABS) and high impact polystyrene (HIPS) plastics from each other. The aim of the this work is to separate blended ABS with HIPS by using salt mixture, in order to do that density of both  plastics have been identified. According to that density of the ABS is 1,067 and HIPS-1.053. We have prepared medium density around 1.055 by adding salt to the distilled water and by floatation of HIPS. ABS resin was separated from HIPS and compared with virgin pellets. Different kind of testing have accomplished in order to check quality and meeting requirements.

Experimental

Flexural and tensile tests were performed at room temperature in the universal Testing Machine QMESYS  QM100TM .test conditions and specimen were determined according to ASTM D – 638 and790 standard for plastic. Flexural conditions were: rate of crosshead motion of 15 mm /min support span of 100 mm, specimens 127*2.7*6.4, were injected from Haitian injection  machine. Tensile test condition were: speed of motion 50 mm/min, specimens have been prepared under ASTM D638 Type I with injection machine Haitian. Density of liquids has tested by densimeter.  Color difference have been tested with Spectrophotometer BYK I (Germany).

Results

Table 1.

Mechanical parameters between raw material and testing samples

Table 2

Specimens have been tested for colors differences with other raw material as well as virgin material ABS RS 670

Test results have shown table below:

In the table 1 shown that separated ABS met all requirements with small deviation of virgin pellets. According to table 2 shown that colour of separated ABS not much different with virgin raw materials and.  It was demonstrated that separated ABS can be useable for making end materials.

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