PVC homopolymer has the disadvantages of poor processing performance, low notched impact strength and poor heat resistance. The addition of various heat stabilizers can overcome the thermal degradation during processing, but it cannot increase the use temperature of the material. Processing aids, internal and external lubricants can reduce PVC melt viscosity and improve processing performance, but it also has a negative impact on Vicat's heat resistance. Blending and filling compounding methods can improve the mechanical properties and heat resistance, but the Vicat softening point of PVC is lower, and the Vicat softening point of rigid PVC is generally 75 to 85°C, so the working environment does not exceed 100°C, and PVC Poor deformability under load also limits
PVC is used as a structural material under heat and stress conditions, which hinders the engineering of PVC. The improvement of static and dynamic thermal stability of PVC will surely expand its application range.

1. Blending modification of heat-resistant polymer
The use of polymer materials to prepare polymer alloys is a simple and effective way to expand the use of polymers. Blending PVC resin with some polymers with good heat resistance can also appropriately improve its heat resistance. The heat-resistant polymer modifiers of PVC mainly include: AS containing phenylmaleimide, AS containing α-methylstyrene (AS is a copolymer of acrylonitrile and styrene), styrene-maleic acid Acid drunk copolymer and heat-resistant engineering plastics.
1.1 N-substituted maleimide commercial molecule heat-resistant modifier
Maleimide (MI) and its derivatives are a kind of rigid and heat-resistant monomers that can undergo self-polymerization. Its homopolymer has a starting temperature of 220-400r for thermal weight loss and is a heat-resistant polymer material. Among N-substituted maleimide, N-phenylmaleimide (PhMI) and N-cyclohexylmaleimide (ChMI) are two important resin modifiers. The modification effect of the former Good, relatively low cost, the latter has a low melting point, good solubility in polymers and monomers, and can be used for heat-resistant modification of polyvinyl chloride resin [t,210N-copolymerization of substituted maleimide Derivatives such as PhMISt-AN terpolymer, MMA-St-PhMI terpolymer, MMA-ChMI copolymer and SMI resin (N-substituted maleic imide modified resin) and ABS resin developed in recent years , MBS resin and acrylic resin as heat-resistant modifiers of polyvinyl chloride can increase its Vicat softening point.
The polyvinyl chloride resin is blended with MMA/ChMI copolymer and a small amount of additives, the Vicat softening point is as high as 128℃, and the MMA-St-Ph-MI copolymer can make the Vicat softening point of PVC reach 145℃, and it has excellent properties. Creep resistance to hot water. Relevant domestic personnel have studied the blending of N-phenylmaleimide/methyl methacrylate/styrene emulsion copolymer and PVC. The Vicat softening point of the obtained blend is linear with the increase of N-PMI content. increase. Adding 25 parts of copolymer to 100 parts of PVC, the Vicat softening point of the blend is 101°C and the glass transition temperature is 91.4°C. From the results of TBA, the blend has only one peak, and its glass transition temperature gradually increases, indicating that the N-PMI copolymer has a certain compatibility with PVC, and the mechanical properties of the blend are also on the rise. The thermogravimetric curve of the blend in the thermogravimetric spectrum in the first stage of the weight loss rate decreases with the increase of the N-PMI copolymer content. At the same time, it can be seen that the slope of the first stage weight loss also varies with the N-PMI copolymer content. Increase and decrease, which means that the thermal decomposition rate decreases, indicating that the N-PMI copolymer has the effect of improving the heat resistance of PVC blends, and it is believed that the weight loss in the first stage of PVC is mainly caused by the removal of HCl, and the hydrogen ion (Or free radical) concentration is the main factor causing weight loss. The greater the hydrogen ion concentration, the faster the weight loss rate; the lower the hydrogen ion concentration, the slower the weight loss rate. The nitrogen atoms in the N-PMI copolymer can balance the hydrogen ions in the system. Therefore, the higher the content of the N-PMI copolymer in the system, the lower the hydrogen ion concentration in the system and the slower the thermal decomposition rate. It can be modified with a-methylstyrene or PhMI to improve the heat resistance of ABS. Among them, a-methylstyrene-modified ABS is easy to decompose, and the heat distortion temperature is low, the highest is 110℃.
Low strength and poor fluidity; while PhMI modified ABS resin is not easy to decompose, the heat distortion temperature is as high as 125 ℃, and the secondary processing performance is good. For example, the Vicat softening point of the blend of ABS resin and PVC modified with ChMI is 106 ℃, while the Vicat softening point of the blend of ABS resin and PVC modified with PhMI is 115 ℃. Because ABS resin contains unsaturated double bonds, its thermal stability and antioxidant properties are poor, so some protective antioxidants and lead salt heat stabilizers must be added. Chen Xian et al. [al] studied the thermal properties of PVC/ABS blended gold, and the results showed that the Vicat heat resistance temperature of PVC and ABS blended greatly increased, and the Vicat heat resistance of blended gold mainly relied on ABS. The amount of plasticizer DOP, DAP has little effect on the thermal stability of the alloy, but has a large negative impact on the heat resistance of Vicat, but has little effect on the static thermal stability. The third element rigid particle SAN has The improvement of the thermal stability of the alloy is not significant, and the addition of processing aid 863 has little effect on the heat resistance of the alloy.
Domestic studies have used Vicat softening to evaluate the heat resistance of the PVC/ABS/CPE blend system in the compatibility and performance study of the PVC/ABS/CPE blend system. The Vicat softening point of the obtained blend system is basically The above are all between the Vicat softening points of PVC and ABS, and increase with the increase of ABS content, which is basically in line with the additive characteristics of compatible plastic alloy properties.
1.2. a-methylstyrene type polymer heat-resistant modifier
a-Methylstyrene (01-M e5I' for short) copolymer is a good heat-resistant modifier. For example, the thermal deformation temperature of a-McST/AN copolymer is close to 120℃, which can generally make the modified resin resistant to The heat temperature can be increased by more than 10℃, and it can even be increased by more than 30℃ for PVC resin. While improving heat resistance, it also improves the impact performance of the resin. Japan's Sumitomo Chemical Company blends polyvinyl chloride, ethylene graft copolymers, and AN/a-methyl styrene copolymers, and the products have excellent properties such as Vicat softening point and elongation. Japan Synthetic Rubber Company conducted a systematic study on the influence of the content of each component in the AN/a-methylstyrene/MMA heat-resistant modifier and the Bd-St-MMA graft copolymer on the heat distortion temperature and found that The increase in the content of α-methylstyrene in the heat-resistant modifier is beneficial to the increase of the deformation temperature, and the increase of the St-MMA content in the graft copolymer is beneficial to the increase of the heat deformation temperature.
1.3. Maleic acid drunk type commercial molecule heat-resistant modifier
The copolymer of maleic acid and styrene and other monomers (SMA) is a heat-resistant modifier with excellent performance. The polymerization methods of SMA mainly include solution polymerization, bulk polymerization and bulk-suspension polymerization. Different synthesis methods have a great influence on the thermal performance of SMA. Bulk polymerization can obtain SMA with the best thermal properties and high polymer quality. Because the SMA molecule contains the oxygen of a lone pair of electrons on the five-membered ring and the Eyl group, it not only improves the heat resistance of SMA, but also interacts with the polyvinyl chloride resin to promote compatibility. Therefore, SMA/PVC Blends have high heat resistance, impact resistance and processability. In the 1980s, the United States, Germany, Japan and other countries successively developed SMA/ Research and development of PVC alloys. When polyvinyl chloride and SMA are blended, as the content of SMA increases, the heat resistance of the blended gold becomes better, and its heat distortion temperature under load is as high as 85°C, which is higher than that of rigid polyvinyl chloride resin. The deformation temperature is increased by 5--8°C, the Vicat softening point is increased by 12°C, the melt viscosity is reduced, and the melt fluidity is improved. In the case of a certain SMA content, as the MA content increases, the dynamic thermal stability of the alloy also improves. In recent years, American companies have developed Elix300, a heat-resistant modifier based on SMA. Adding 30% of SMA to polyvinyl chloride can increase the Vicat softening point to 104°C. A company mixed 100 parts of PVC, 110 parts of SMA, 4 parts of organotin, and 2 parts of mercaptan to form a composition. The Vicat softening point is 113℃, and the carbonization time at 220℃ is 20 min. The composition of the stabilizer is only 82°C and 10 min. In addition, SMA can be modified by rubber, and then mixed with PVC. For example, the heat distortion temperature of the mixture obtained in the two patents of Doak can reach 88°C, and it also has higher impact strength.
1.4. Blending with heat-resistant engineering plastics
Generally, materials with good heat resistance, especially engineering plastics, have a relatively high processing temperature, while PVC materials are prone to degradation under the processing conditions of 190℃. The large difference in processing temperature has become the biggest obstacle to the blending of PVC and engineering plastics. Therefore, research reports in this area are very rare. U.S. DuPont Packaging and Industrial Polymers Company uses EnBACO (ethylene-acrylic acid ester carbon monoxide copolymer) and EnBACD-g-MAH (EnBACO grafted maleic acid) as compatibilizers, which are added separately from different inlets PA and PVC and the method of segmented temperature control successfully produced PA6/PVC, PA1212/PVC, PA12/PVC and two kinds of special nylon and PVC blending gold MPMD6/PVC and MPMD12/PVC, opening up the engineering plasticization of PVC New areas. Domestic researchers learn from DuPont’s technology
Using EnBACD-g-MAH as a compatibilizer, low melting point ternary copolymer nylon NT (1010 salt 1 caprolactam/66 salt = 7/1/2) was blended with PVC to obtain a new type of Super tough, high fluidity, high heat resistance PVC/nylon alloy. Although the Vicat softening point of polyvinyl chloride and polyvinyl chloride containing compatibilizers is relatively low, the high heat resistance temperature of nylon still makes the alloy have better heat resistance than polyvinyl chloride. For example, when the content of nylon and polyvinyl chloride compatibilized with EnRACO-g-MAH is 50/50, the Vicat softening point reaches 120 ℃ on the basis of better performance such as impact. However, the Vicat softening point of this alloy under 5 loads is only 64°C, so the heat resistance under high loads is still relatively poor.