Plastics are all around us because they have many advantages over other materials. Polyvinyl chloride (PVC) is the most commonly used. When a suitable liquid plasticiser is added, a plastisol is obtained. Various blowing agents, stabilisers and other additives can be added to achieve certain desired properties of the plastisol. There are two main types of blowing agents: physical and chemical blowing agents. For my dissertation research I used a chemical foaming agent.
In my thesis I wanted to determine the influence of temperature as the most important process parameter in the production of plastisol using a chemical blowing agent. I exposed suitable liquid mixtures of PVC and liquid plasticiser and other additives to selected temperature conditions. During exposure of the plastisol samples to the selected temperature conditions, individual samples of identical plastisol blends were removed from the oven and analysed to determine the optimum exposure times of the plastisols at a given temperature or to determine the optimum process temperature condition(s). In addition to varying the oven temperature and the exposure time of the samples at a given temperature, I also varied the amount of blowing agent in the plastisol blend at the beginning of my work to obtain a suitable blend for the study. I carried out a stepwise isothermal heating of the samples at three different temperatures, preparing several samples of an identical plastisol mixture in the appropriate moulds and removing them from the oven to room temperature after a certain period of exposure to the selected elevated temperature. I also carried out various combinations of step changes in temperature during the plastisol production process. This was done by rapidly moving the plastisol samples from the oven at temperature T1 to the oven at temperature T2.
The results were analysed using a light microscope, a digital Shore 0 hardness tester, a differential dynamic scanning calorimeter (DSC) and an in-line electron microscope.
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