One way on reinforcing plastic is to add fibred glass to it. This makes it much stronger and is generally referred to as   G.R.P. (glass reinforced plastic).
With there being so many types of plastic it is a good idea to use simple tests on them to try and find out what they are. These simple tests are as follows
1. Appearance - looking at it to establish its general characteristics.
2. Rigidity - How hard is it, is it easy to scratch, does it cut or break easily.
3. Bending - how does it recover (if at all) when you try to bend it.
4. Heating - Does it soften, remain hard, smell when heated.
5. Burning - Does it resist burning, burn, splutter, burn smoothly, give off smoke/fumes.
6. Density - Place a piece in water to see if it sinks or floats.