Study on PVC modified by the hottest polyurethane

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Research on polyurethane modified polyvinyl chloride


polyvinyl chloride (PVC) has the advantages of light weight, high strength, oil resistance, chemical resistance, transparency, flame retardancy, excellent electrical properties, and low price. It is widely used in all walks of life [1,2], from soft thermoplastic elastomers, plastic films, adhesives, coatings to hard plastic pipes and plates. There are many kinds of PVC products, but in general, they can be divided into soft PVC products and hard PVC products [3]. Worldwide, the output of hard PVC is higher than that of soft PVC, while the output of soft PVC plastic in China is higher than that of hard PVC. Most of the PVC resins with an annual output of more than 100 million tons are used to produce soft PVC products in scientific research institutions, and are mostly used in wire and cable, shoe soles, artificial leather and other fields. However, domestic soft PVC products generally have shortcomings such as poor resilience, poor solvent resistance, poor heat resistance and poor friction resistance

polyurethane elastomer has the advantages of soft PVC such as high elasticity, high wear resistance, excellent low temperature resistance and solvent resistance, which are lacking [4]. The higher the ability of polyurethane to resist brittle fracture of PVC welding structure is, the better the performance and practical value of soft PVC material will be significantly improved and its application field will be expanded. However, the traditional modification method is to prepare thermoplastic polyurethane elastomer first, and then modify it by physical blending with PVC resin. In this way, although the performance is improved, the cost is also increased accordingly. This paper studies the one-step preparation of PVC/PU blends. Polyurethane elastomers are formed during extrusion and blended with PVC at the same time, which can improve and improve material properties and reduce costs

1 experimental part

1.1 main raw material

isocyanate MDI, Yantai synthetic leather factory; Polyether polyol, Shanghai Gaoqiao Chemical Plant; Polyester polyol (PPE), self-made; Chain extender BD, Qingdao chemical light company; Polyvinyl chloride (PVC), chlor alkali plant of Qilu Petrochemical Company; Di salt, tri salt, calcium stearate (barium), plasticizer DOP, paraffin, etc

1.2 experimental instrument

gh-l0 high-speed mixer, Beijing Plastic Machinery Factory; Sk-j60 rubber mixer, Shanghai Rubber Machinery Factory; Ds-45a twin screw extruder, Shanghai Machinery Factory; A-25 plate pressure forming machine; Ag-2000a universal testing machine, Shimadzu company, Japan; LX - 77A shore hardness tester; FTIR infrared spectrometer, NEC Corporation

1.3 molding process

grind the PVC ingredients into a high-speed mixer and mix them for 10 ~ 15 minutes, then add isocyanate, polyol, chain extender, etc. mixed in a certain proportion, continue mixing for 10 minutes, add the mixed materials into the extruder, and the materials react in the extrusion process at a certain temperature and speed; The extrudate is granulated, plasticized on the rubber mixer, and then hot pressed into pieces on the pressure forming machine, and then the samples are prepared according to the requirements of the test standards for performance testing

2 results and discussion

2.1 study on reactive extrusion process

2.1.1 effect of extrusion speed on blending reaction

the temperature of homogenization section of extruder was controlled at 180CC, and the effects of screw speeds of 20, 30, 40, 50, 60, 70 and 80R/min on the reaction process were investigated. The test results show that when the screw speed is large (70, 80R/min), there is no characteristic N-H vibration absorption peak of polyurethane in the infrared spectrum of the extrusion, indicating that polyurethane is not generated. With the decrease of screw speed, that is, the increase of reaction time, the characteristic N-H stretching vibration peak [5] (see Figure 1) of unassociated and associated polyurethane appeared at 3400cm-1 and 3320cm-1 in the infrared spectrum of the extrudate, and its peak shape gradually increased. When the speed fell below 40R/min, the peak shape basically remained unchanged. This shows that the hydroxyl of polyol reacts with isocyanate, and the degree of reaction increases with the decrease of screw speed. When the speed drops to 40R/min, the formation reaction of polyurethane is basically complete

2.1.2 effect of temperature on blending reaction. Increasing the temperature is conducive to the formation of polyurethane. When the homogenization section temperature of the extruder is increased from 180 ℃ to 190 ℃. When the screw speed was 60R/min, the N-H stretching vibration peak that did not appear on the infrared spectrum of the extrudate appeared at 3400cm-1 and 3320cm-1. However, the temperature should not be too high. When the temperature reaches 200 ℃, PVC decomposition intensifies and affects the final performance of the products. The test shows that the homogenization section temperature of the extruder is controlled at 180 ℃ ~ 190 ℃, and the screw speed of the extruder is 40 ~ 50R/min, which is conducive to the formation of PU

2.2 study on the properties of PVC/PU by reactive extrusion

2.2.1 effect of polyols on the properties of PVC/PU

when PVC is modified with polyurethane (PU), in order to make PVC/PU plastic have good comprehensive properties, it is necessary to make Pu and PVC have a certain degree of compatibility, that is, the solubility parameters between the two components should be close [6]. The solubility parameters of Pu are mainly determined by polyols, and the polyols used to synthesize Pu are mainly polyether polyols and polyester polyols. Comparing polyether polyol and polyester polyol, under the condition of PVC/pu=80:20, it is found that polyether Pu has poor compatibility with PVC, while polyester Pu has good compatibility with PVC. Therefore, polyester polyols were selected in this experiment, and the effects of different polyester polyols with greater deformation closer to the fracture on the properties of PVC/PU blends were investigated. The results are listed in Table 1. It can be seen from table 1 that the tensile strength, tear strength and hardness of PVC/PU plastics made of ppe-3 polyester diol are the best, and the properties of PVC/PU blends made of other polyesters are not different. This is because the polyurethane produced with ppe-3 polyester diol has good compatibility with the selected PVC

2.2.2 effect of PVC molecular weight on the properties of PVC/PU

Table 2 shows the properties of PVC and polyurethane synthetic plastics with different molecular weights. It can be seen from table 2 that the PVC/PU Blend plastic synthesized from PVC resin with an average polymerization degree of 1300 has the best performance, and its tensile strength reaches 28.5mpa

2.2.3 effect of polyurethane dosage on the properties of PVC/PU Table 3 shows the effect of different dosage of polyurethane on the properties of PVC/PU plastics. It can be seen from table 3 that with the increase of the amount of polyurethane, the mechanical properties of PVC/PU blended plastics will gradually improve no matter what position you take, but the product cost will also increase accordingly. Therefore, it is necessary to choose the appropriate amount of polyurethane to produce PVC/PU blended plastics with moderate price and good comprehensive properties. Experiments show that the dosage of polyurethane is generally about 20% of that of PVC

3 conclusion (1) by studying the reactive extrusion process, it is determined that the screw speed is 40 ~ 50R/min and the homogenization section temperature of the extruder is 180 ~ 190 ℃

(2) the performance study shows that PVC/PU soft plastics with moderate price and excellent comprehensive properties can be prepared by reactive extrusion by selecting PVC with an average molecular weight of 1300 and polyurethane produced with ppe-3 polyester diol, and controlling PVC/pu=80:20

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