This question does need specialized knowledge . I only know that the most commonly used plastic in eyeglass frames, is cellulose acetate which is relatively inexpensive, easy to work with, and comes in a wide variety of colors, textures, and patterns. The material is easily adjusted but tends to get brittle with age.
Dude, I think you'd better have a good understanding of the primary, secondary and tertiary industries first. In our country, the primary industry is agriculture which includes planting industry, forestry, animal husbandry, sideline and fishery. The secondary industry is industry and construction which includes mining and quarrying, manufacturing industry, tap water, electricity, steam, gas and so on. The tertiary industry is all the industries except the primary and secondary industries. I think glasses belong to the tertiary industry.
I think maybe you want to know the procedure of making a pair of plastic frame. The main material for plastic frames is cellulose acetate. There are acetate frames and plastic frames. Acetate frames are lighter, harder, and durable and won't fade after too much exposure to sunlight. Besides, they are not so easy to deform when compared with plastic frames. While plastic frames are made by modeling machines though they are also made by cellulose acetate.
There are two ways to make plastic frames. The first one is to cut the plastic frames and arms of the frames then put them together with hinges. The acetate frames that made in this way are much better but the cost is higher. This way of processing is suitable for small batch production. The second way of producing is to soften the plastics and then put them into plastic injection molds. This way of processing will cost less and it is suitable for mass production.
The plastic frames are made out of cellulose acetate. Though the main material is the same, but the quality of plastic frames may have great differences. So before buying a pair of sunglasses, you'd better have a good look of the frames. And ask the salesman whether they are acetate frames or not. Acetate frames are more expensive but they are more durable. Hope this helped!