免费观看国产午夜激AV_av狼友国产在线观看_久热中文字幕在线播放_日本精品一区免费中文视频

Generally speaking, natural rubber refers to an elastic solid made from natural rubber latex collected from the Brazilian rubber tree through processing steps such as coagulation and drying. Natural rubber is a natural polymer compound with cis-1,4-polyisoprene as the main component. Its rubber hydrocarbon (cis-1,4-polyisoprene) content is above 90%. It also contains A small amount of protein, fatty acids, sugar and ash.