Views:0 Author:Site Editor Publish Time: 2021-04-03 Origin:Site
Various excellent properties make polyvinyl alcohol one of the most popular substances in the world. There are two important indicators of polymerization degree and alcoholysis degree. The textile industry uses slightly lower polymerization degree, the adhesive industry uses high polymerization degree, and also uses low alcoholysis degree. What is good quality polyvinyl alcohol? Our polyvinyl alcohol is your best choice.
The properties of polyvinyl alcohol are affected by the chemical structure, degree of alcoholysis, and degree of polymerization.
The degree of polymerization of a good polyvinyl alcohol is divided into ultra-high degree of polymerization (molecular weight of 250,000 to 300,000), high degree of polymerization (molecular weight of 170 to 220,000), medium degree of polymerization (molecular weight of 120,000 to 150,000) and low degree of polymerization (2.5 to 250,000). 35,000). The degree of alcoholysis is generally 78%, 88%, and 98%. The degree of alcoholysis for partial alcoholysis is usually 87% to 89%, and the degree of alcoholysis for complete alcoholysis is 98% to 100%. The thousands and hundreds digits of the average degree of polymerization are often put in the front, and the percentage of the alcoholysis degree is put in the back. For example, 17-88 means that the polymerization degree is 1700 and the alcoholysis degree is 88%. Generally, as the degree of polymerization increases, the viscosity of the aqueous solution increases, and the strength and solvent resistance after film formation increase, but the solubility in water and the elongation after film formation decrease. The relative density of polyvinyl alcohol (25℃/4℃) is 1.27～1.31 (solid), 1.02 (10% solution), melting point is 230℃, glass transition temperature is 75～85℃, it will change color when heated to above 100℃ in air , Embrittlement. When heated to 160～170℃, dehydration and etherification will lose its solubility, and it will start to decompose when heated to 200℃. Over 250°C it becomes a polymer containing conjugated double bonds. Refractive index 1.49～1.52, thermal conductivity 0.2W/(m·K), specific heat capacity 1～5 J/(kg·K), resistivity (3.1～3.8)×10 Ω·cm. It is soluble in water and generally needs to be heated to 65～75℃ in order to dissolve completely.
Solubility: PVA is soluble in water, the higher the water temperature, the greater the solubility, but it is almost insoluble in organic solvents. The solubility of PVA varies with the degree of alcoholysis and degree of polymerization. PVA with partial alcoholysis and low polymerization degree dissolves extremely fast, while PVA with complete alcoholysis and high polymerization degree dissolves slowly. As a general rule, the degree of alcoholysis is greater than the degree of polymerization for the influence on the solubility of PVA. The PVA dissolution process is carried out in stages, namely: affinity wetting-swelling-infinite swelling-dissolution.
Film formation: PVA is easy to form a film, and its film has excellent mechanical properties. The tensile strength of the film increases with the increase of the degree of polymerization and alcoholysis.
Adhesion: PVA has good adhesion to hydrophilic cellulose. In general, the higher the degree of polymerization and alcoholysis, the stronger the bonding strength.
When the thermally stable PVA powder is heated to about 100°C, the appearance gradually changes. Part of the alcoholysis PVA starts to melt at around 190°C and decomposes at 200°C. The completely alcoholysis PVA starts to melt at around 230℃ and decomposes at 240℃. Thermal cracking experiments show that the lower the degree of polymerization, the faster the weight loss; the higher the degree of alcoholysis, the shorter the decomposition time.
After more than 40 years of development, China's PVA industry has become the world's largest PVA producer. With technical routes such as petroleum ethylene method, natural gas acetylene method and calcium carbide acetylene method, our PVA quality is very advanced. You can choose us with confidence.