They're made of plasticized cellulose acetate which doesn't mean that they'll stay whole forever.

它们是由化醋酸制成的，这并不意味着它们会永远完整地存在。

After numerous failed attempts to make use of PVC, an American successfully plasticized it in the 1920's and began experimenting with it as a cheaper and more durable alternative to rubber and to other plastics.

过无数次利用PVC的失败尝试，一位美国人在20世纪20年代成功地化，并开始试验更便宜耐用的PVC作为橡胶和他料的替代品。