国产99久久九九精品无码_久久婷婷综合日韩综合国产_亚州性无码不卡免费视频_国产人人在线成视频

The country’s support for rural areas is increasing. In rural areas, the sewage treatment facilities for septic tanks and toilets in rural areas are not perfect. Sewage septic tanks and public toilets in farms lead to odor, fecal agglomeration, and partial discharge of sewage. Some ... Read More

PA66 engineering plastic is a condensation polymer that uses hexamethylenediamine and adipic acid as monomers and is connected by amide bonds. It has high strength, good resistance, and excellent performance such as wear resistance. It is used in automobiles, electronics and textiles. Has a wide ... Read More

PA66 engineering plastic is a high polymer with a relatively high molecular weight. The molecular weight directly affects its physical and chemical properties such as mechanical strength and heat resistance. The method of estimating molecular weight is to determine the relative viscosity of high polymers. ... Read More