Due to the poor cold resistance and low temperature impact resistance of PVC, the lower temperature limit of use of hard PVC is generally Celsius, which limits the application of PVC materials in some aspects. Through the adjustment of PVC resin and additives, it can effectively improve the cold resistance of PVC plastics and meet the needs of low temperature.

1 PVC resin

PVC resin is a kind of non-crystalline, polar polymer. Its glass transition temperature is 75~105oC. The higher the relative molecular mass, the higher the viscosity, the corresponding gravity or entanglement of PVC macromolecular chain van der Waals. Increase, PVC segment growth, the better the low temperature resistance of the material.

In the conventional PVC formula, if it is only necessary to cope with the cold winter weather in the north, it is possible to select a PVC resin with a slightly higher viscosity, that is, a slightly larger average molecular weight, which may be a PVC with a higher viscosity value in the same grade or a lower grade resin.

In addition, in some special requirements, such as blood bags that can withstand -30oC, high polymerization degree PVC resin can be used because high polymerization degree PVC has larger crystallinity and class than conventional PVC resin. The cross-linking structure makes the sliding between macromolecules difficult, the elasticity increases, the molecular weight increases, the intermolecular van der Waals force and the intramolecular chemical bonding force increase to obtain excellent cold resistance.

2 plasticizer

As an important formula component of PVC soft products, plasticizers have great influence on the performance of soft products. If the products are required to be used at low temperatures, the type of plasticizer must be selected. At present, mainly used as a cold-resistant plasticizer are a fatty acid dibasic acid ester, a phthalic acid ester of a linear alcohol, a fatty acid ester of a glycol, and an epoxy fatty acid monoester. It has been reported that N,N-disubstituted fatty acid amides, cycloalkane dicarboxylates, and chloromethoxy fatty acid esters are also cold-resistant plasticizers having excellent low-temperature properties.

Some studies have pointed out that [for the purpose of improving the cold resistance toughness and low temperature elongation of the film, it is preferred to use a cold resistant plasticizer together with hexamethylphosphoric triamide. Because hexamethylphosphoric triamide is not a cold-resistant plasticizer itself, it can effectively reduce the freezing point of various plasticizers and achieve the purpose of strengthening the cold resistance of the film.

3 modifier

An effective way to improve the low-temperature impact strength of PVC is to add a polymer having a low glass transition temperature and exhibiting high elasticity at room temperature, collectively referred to as a modifier. The high polymer added should have similar solubility parameters to PVC, and have a certain mutual solubility ability, and can form a blend of two structures, thereby improving the low temperature impact strength of the product.

Studies have shown that CPE can improve the low temperature performance, impact strength and so on. As the amount of CPE increases, the impact properties of PV C products will gradually increase. When the dosage is increased to a certain extent, the low temperature impact performance of the PV C product tends to be stable, and the appropriate performance price ratio is achieved at about 8 or 9 parts. As the amount of powdered nitrile rubber (NBR) increases, the low-temperature impact strength of hard PVC is gradually increased. EVA has good flow performance, low glass transition temperature, good low temperature toughening effect, but high cost. ACR has excellent low-temperature impact strength and weather resistance, and can improve the appearance of the product. Generally, 5 parts can be used to achieve good results. The high impact type MBS has a low glass transition temperature and has a good improvement effect on the low temperature brittleness of the PVC material, but has poor weather resistance. ABS can improve the low temperature impact strength of PVC materials while improving the appearance of the products. In addition, some substances such as SBS which contain a rubber phase and have a low glass transition temperature also have an effect of improving the impact strength and cold resistance of PVC.

At present, the cold resistance of modified soft PVC shows that the cold resistance of blended soft PVC is obviously affected by the variety and dosage of polymer modifier. Through various methods, it was found that polymer modifiers such as Elvaloy 711 (ethylene-vinyl acetate carbon monoxide copolymer), NBR-26 (blocky butadiene rubber), and Chemigum P83 (pre-crosslinked powdered butadiene rubber) can be significantly improved. The cold resistance of soft PVC, and some polymer modifiers such as CPE and EVA with low VA content will impair the cold resistance of soft PVC. The butyl rubber modifier can improve the low temperature performance of soft PVC immersed in gasoline by improving the resistance of the flexible PVC to gasoline (gasoline).

Cold-resistant agents introduced on the market, such as K-175C and N-550C, are actually a styrenic modifier developed to improve the low-temperature flexibility and impact strength of PVC. Due to its low glass transition temperature and good compatibility with PVC, it has certain plasticizing and toughening effects. Therefore, after adding in PVC, it can improve and improve the low temperature performance of PVC.