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

它们是由塑化醋酸纤维素制成，这并不意味着它们会永远完整地。

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PVC失败尝试，一位美国人20世纪20年代成功地将其塑化，并开始试验将更便宜耐PVC作为橡胶和其他塑料替代品。