The application of polymer plasticizer in PVC
(1) PVC / polyester plasticizer
Polyester plasticizer is a kind of polymer plasticizer used earlier. It is mainly prepared by condensation reaction between dicarboxylic acid and diol. There are kinds of adipic acid polyester and phthalic anhydride polyester. The molecular weight of polyester plasticizer is about 3000. And it can reduce the migration of small molecular plasticizer in soft PVC. Polyester plasticizer improves the processability of PVC and is suitable for oil, water and solvent resistant plastics such as leather, toys, medicine and food. When applied in soft PVC, the quantity can reach 70%.
Relative molecular mass and branching degree influence the plasticizing effect of polyester plasticizer. With the increase of relative molecular weight of the polyester plasticizer, the glass transition temperature of the soft PVC decreases, the plasticizing effect and heat resistance, the solvent resistance are improved. The increase of the polyester plasticizer's branching degree also improves the heat resistance of the soft PVC.
In PVC / polyester sol system, the optimum addition amount of polyester (PPA-polyadipylene adipate) is 50 / 70 (mass fraction), and the thermal stability of the sol is better under these conditions. In order to avoid the extraction of plasticizer by organic solvent, the traditional small molecular plasticizer system of PVC / polyester plasticizer can be used in the painting process of automobile production, and good results can be obtained. The shear strength of PVC / DOP / filler plasticsol can also be improved when terminated polyurethane is used as plasticizer additive.
(2) PVC / LNBR
Liquid acrylonitrile-butadiene rubber (LNBR) is a copolymer of butadiene and acrylonitrile, which is synthesized by free radical emulsion polymerization. The first species were non-functional groups and random functional groups, and later mainly end functional groups, such as hydroxyl terminated liquid acrylonitrile-butadiene rubber (HTBN), carboxyl liquid acrylonitrile-terminated butadiene rubber (CTBN), mercapto liquid nitrile butadiene rubber (MTBN) and amino liquid butadiene acrylonitrile rubber (ATBN), etc. When the rubber with end functional group is cured, the functional group at the end of the molecule participates in the crosslinking, which makes the crosslinking network of vulcanizate.There is no free chain end in the complex, the relative molecular weight between crosslinking points is larger than that of ordinary rubber, the structure is regular, and there is no short chain, so the softness is very good. The domestic brands are mainly Lanzhou Petrochemical liquid butadiene-26, liquid butadiene-40 and carboxyl liquid butadionitrile. The mass fraction of acrylonitrile was 23%~27%, 30%~40% and 30%~35% respectively.
When LNBR was added into PVC paste resin instead of phthalic acid plasticizer, the plasticized PVC material with good oil resistance and solvent resistance could be prepared. The material not only had high strength and low deformation, but also had a very low extraction rate in n-heptane. Can be used to contact with food industry.
Liquid acrylonitrile-butadiene rubber (LNBR) makes up the defect that solid NBR is not easy to be mixed with PVC paste resin, so it can be used to modify PVC foam plastics. 0% (mass fraction) of LNBR can greatly improve the tensile strength, elongation at break and hardness of PVC foam plastics. But the foaming rate decreased.
LNBR can also improve the elasticity of PVC while replacing ordinary plasticizers such as DOP. The film was prepared by adding LNBR into PVC / DINP / 100 / 80) mixture and the mechanical properties were tested. When the content of LNBR was 20 phr, the elongation at break was twice as high as that without adding it, and the tensile strength did not decrease.