The clock project uses acrylic plastic - the real name for 'acrylic' is polymethyl methacrylate - and this is an example of a THERMOPLASTIC. Plastics that we will use in school group into two main classes: one is THERMOSETTING plastics and the other is THERMOPLASTICS. There are many different kinds of 'plastics' and many are known by their initial letters. PVA for instance is polyvinyl acetate and PVC is polyvinyl chloride. Some plastics have a 'trade' name that has stayed with them; NYLON is really polyamide and another name for polymethyl methacrylate is the rather better known, PERSPEX.
So where do plastics come from ? Many are chemical products coming from oil as one product coming from the process of making fuels such as petrol, gas, diesel and paraffin. The oil and gas supplies we have are fossil fuels and were laid down millions of years ago when plant materials were buried without rotting away. Since we use so much plastic material today this is one reason why we should preserve our fossil fuel supplies rather than squander them.