Views: 264 Author: Vickey Publish Time: 2023-06-06 Origin: Site
PVOH, PVA, or PVAl are synthetic polymers that dissolve in water. Its idealized chemical structure is [CH2CH(OH)]n. As a thickener and emulsion stabilizer in polyvinyl acetate (PVAc) adhesive formulations, it is utilized in papermaking, textile warp sizing, a variety of coatings, and 3D printing. It has no color (it is white) and no smell. It is frequently provided as a solution in water or as beads. PVA solution may be repeatedly frozen and thawed to produce very strong, ultrapure, biocompatible hydrogels without the need for an externally supplied crosslinking agent. These hydrogels have been utilized for a number of purposes, including vascular stents, cartilages, contact lenses, etc.
As a result of its biocompatibility, low propensity for protein attachment, and low toxicity, PVA is utilized in a range of medicinal applications. Contact lenses, eye drops, and cartilage replacements are a few examples of specific usage. Suspension polymerizations are aided by the introduction of polyvinyl alcohol. Its usage as a protective colloid in PVAc dispersions is its main application in China. Its primary use in Japan is the creation of vinylon fiber. Because it doesn't require oil to make, this fiber is also produced in North Korea for self-sufficiency purposes. Film for photos is yet another use.
Polymers based on PVA are often used in additive manufacturing. For instance, the pharmaceutical business has a lot of promise for 3D-printed oral dose forms.When PVA is utilized as a binder, it is feasible to produce drug-loaded tablets with altered drug-release properties. In a uterine fibroids embolectomy, it can also be employed as the embolic agent.
Household sponges that absorb more water than polyurethane sponges frequently employ PVA. For gluing porous materials like wood, paper, and fabric, PVA glue is frequently employed.
PVA is not made by polymerizing the homologous monomer, vinyl alcohol, as is the case with most vinyl polymers since vinyl alcohol is thermodynamically unstable when it comes to acetaldehyde tautomerization. Instead, polyvinyl acetate or, occasionally, other vinyl ester-derived polymers having formate or chloroacetate groups instead of acetate groups are hydrolyzed to create PVA.The conversion of the polyvinyl esters is usually conducted by base-catalysed transesterification with ethanol:[CH2CH(OAc)]n + C2H5OH → [CH2CH(OH)]n + C2H5OAc.
The properties of the polymer are affected by the degree of transesterification.
Worldwide consumption of polyvinyl alcohol was over one million metric tons in 2006.
PVA is a crystallin substance that is abrasive. Excellent film-forming, emulsifying, and adhesion qualities are possessed by polyvinyl alcohol. Additionally, it is solvent, oil, and grease resistant. It offers excellent oxygen and scent barrier qualities, high tensile strength, and flexibility. These characteristics, however, are influenced by humidity: water absorbed at higher levels of relative humidity works as a plasticizer, reducing the polymer's tensile strength while enhancing its elongation and rip strength.
The toxicity and biodegradation of PVA are of interest because of its widespread use. Fish are poisoned by solutions with more than 5% PVA in them. Biodegradation takes time.