Chlorinated Polyvinyl Chloride.CPVc (Chlorinated Polyvinyl Chloride.CPVc) resin was first industrialized by IG Farben in Germany in the mid-1930s. The early production method used was to chlorinate PVC in a solution and use this method to produce CPVC resin is more soluble in solvents than PVC resin. In the 1960s, the aqueous suspension chlorination method was adopted. CPVC is an important modifier of PVC. The chlorine content in its molecular structure is significantly higher than that of PVC resin, generally 61% to 68%. Because its molecular structure contains more chlorine atoms, the glass transition temperature (T g) and heat distortion temperature of CPVC resin are higher, so the heat resistance and maximum use temperature are significantly higher than that of PVC; at the same time, CPVC resin also has excellent Mechanical properties, chemical resistance, non-conductivity, flame-retardant properties and the lowest smoke generation characteristics are new materials with excellent performance.

The heat resistance of CPVC is 20-40℃ higher than that of PVC on average. Using this feature, it can improve the heat resistance of PVC after blending with PVC. In addition, PVC/CPVC blends have better compatibility. There are many reports on the research and application of PVC/CPVC blends abroad. The PVC/CPVC alloy developed by Goodrich can be used to manufacture molded sheets, trays, fan covers, electrical parts and casings, and commercial products by injection, extrusion, calendering and pressing. Machine shells, pipes, communication equipment and auto parts, etc.[7]. Sekisui Chemical Industry Co., Ltd. adds 5 to 3 parts of PVC and a small amount of PMMA or methyl methacrylate and styrene polymer or SAN copolymer to CPVC to obtain mechanical strength, heat resistance, weather resistance, and chemical resistance Materials with good resistance, flame resistance and transparency. Used in the manufacture of building materials, auto parts, etc.

The author chooses CPVC and PVC as the main materials to study the effects of PVC/CPVC blending ratio, filler variety and amount on the mechanical properties of PVC/CPVC alloy system, and at the same time use scanning electron microscope to analyze the microstructure of PVC/CPVC alloy .

1. Experiment
1.1 Experimental materials
CPVC: chlorine content 66%; PVC: S-1000; dibasic lead phosphite, tribasic lead sulfate, barium stearate, calcium stearate: industrial products; stearic acid: industrial products; organic Tin stabilizer: T-137; active light CaCO: fineness of 1,000 mesh; acrylic impact modifier: KM355P; acrylic processing modifier: K125P; paraffin wax: P1; talc; clay: fineness 325 mesh; diatomaceous earth; mica: 800 mesh fineness.
1.2 Main instruments and equipment
Double-roller plastic mixing machine: SK-160B; 25t flat vulcanizer: QLB-50×350×2; punching machine; electronic balance: YP1200; electro-optical analytical balance: TG328B; universal prototype machine: HY-w; electronic stretching Testing machine: CMT5254; Universal material testing machine: DLY-6; Impact testing machine: xJJ-50; Oven: DGF30/7-Ⅱ; Scanning electron microscope: sx-40, working voltage 20kV.
1.3 Sample preparation and testing
1.3.1 Sample preparation
Accurately weigh the raw materials, processing aids and fillers according to the formula requirements, and mix them evenly with a high-speed mixer. Control the temperature of the front roller of the open plastic mill to 180°C, the temperature of the rear roller to 170°C, and the roller gap to be 1-2 mm, and add the evenly mixed powder to the preheated plastic mill. After the PVC/CPVC plasticization wraps the roller, adjust the roller gap to about 0.3 mm and hit the triangle wrap 3 times. After the blend is uniform, a 0.5-1.0 mm sheet will be produced for use. Control the temperature of the 25 t flat vulcanizer to 180°C. After the mold is preheated, put the PVC/CPVC blended sheet into it, and then put it in the flat vulcanizer. Heat it at 5-6MPa for 10 minutes, then heat it at 12-13 MPa for 10 minutes, then quickly take it out, move it to another flat vulcanizer without heating, and cool to room temperature under pressure. After the pressed sample is placed for 24 hours, samples are prepared and tested according to national standards.
1.3.2 Performance Test
The tensile performance test is carried out according to GB/T 1040-92, the bending performance test is carried out according to GB/T 9341-88, the cantilever beam impact performance test is carried out according to GB/T 9432-88, and the heat distortion temperature (HDT) test is carried out according to GB/T 1634-89.

1.3.3 Microstructure characterization of alloy system
The cross section of the impact sample of PVC/CPVC alloy is selected, and its microstructure is observed with a scanning electron microscope (SEM). The acceleration voltage of the SEM is 20 kV.

2. Results and discussion
2.1 The effect of blending ratio on the performance of PVC/CPVC binary alloy when lead salt stabilizer
In the experiment, the lead salt stabilizer was first selected to discuss the influence of the blending ratio on the performance of the PVC/CPVC binary alloy. The results are shown in Table 1.

The experimental results show that when (PVC): m(CPVC) changes from 100:0 to 70:30, as the content of CPVC increases, the tensile strength, bending strength, and thermal deformation temperature of the PVC/CPVC binary alloy system ( The maximum bending normal stress is 1.82 MPa and 0.45 MPa, respectively), etc., are increasing. Among them, the increase of tensile strength and flexural strength were 7% and 18%, respectively, and the increase of heat distortion temperature was less than 5%; and also with the increase of CPVC content, the impact strength and elongation at break of the system showed a decreasing trend. (PVC): When (CPVC)=70:30, the impact strength of the system is only 66.67% of that when PVC alone is used, and the elongation at break decreases even more, at this time only 45% of the original. This is because the CPVC content in the system increases, and the rigidity and heat resistance of CPVC lead to the increase in the rigidity and heat resistance of the alloy.

Table 1 The effect of different blending ratios on the properties of PVC/CPVC binary alloys with lead salt stabilizers

Basic formula (parts by mass, F l Division): PVC/CPVC 1O0, 3PbO 3, 2PbO3, BaSt: 15 KM355P 8, KI25P 2, filler 9, lubricant (1 7.

Figure 1 is (PVC): (CPVC)=1O0:0, 90:10, 80:20, 70:30, the SEM photo of the cross section of the alloy impact sample enlarged 1500 times. It can be seen from Figure 1 that the compatibility of PVC/CPVC alloy is better, which is the same as reported in the literature. In comparison, when (PVC): (CPVC)=90:10, 80:20, the dispersion effect of the system is slightly worse. The particle size and uneven dispersion appear in the alloy system. But as the amount of CPVC increases, the uniformity of the alloy system is greatly improved, especially when (PVC): (CPVC)=70:30, the dispersion of the two is more uniform.

Figure 1 SEM pictures of the cross-sections of PVC/CPVC alloy impact samples with different blend ratios (1 500 times)


2.2 The effect of blending ratio on the performance of PVC/CPVC binary alloy when containing organotin stabilizer When using organotin stabilizer, the formula and mechanical properties of PVC/CPVC alloy are shown in Table 2.

The results show that under the action of organotin stabilizers, when (PVC): (CPVC) changes from 1O0:0 to 70:30, with the increase of CPVC content, the tensile strength of the pvc/CPVC binary alloy system Impact strength and elongation at break both show a trend of first decline and then rise; on the contrary, bending strength shows a trend of first rise and then fall. Two trends appear when (PVC): (CPVC)=80:20. At this time, the impact strength and elongation at break of the system are reduced to 50% of the PVC alone, and the tensile strength is only 93% of the original. , While the bending strength has increased by 5%. In addition, with the increase of the CPVC content in the blending ratio, the heat distortion temperature of the system continues to rise, (PVC): (CPVC)=70:30, under different bending normal stresses (1.82MPa and 0.45 MPa) Compared with PVC, the heat distortion temperature increased by 1.3 ℃ and 5.6 ℃ respectively.

Table 2 The effect of different blending ratios on the mechanical properties of PVC/CPVC alloy when containing organic tin stabilizers

Basic formula: PVC/CPVC 1O0, organotin T-137 2.5, KM355P 8, k125P 2, filler 9, lubricant 1.2.

Through the comparative analysis of the above two sets of experimental data, it is found that under the action of the organotin stabilizer, the yield strength, tensile strength, impact strength, elongation at break and bending strength of the alloy have no obvious changes. Although organotin stabilizers have a greater effect on the heat distortion temperature, they are not as effective as lead salt stabilizers on binary alloy systems. The elongation at break of the binary alloy system using organotin stabilizer is also lower than that of the binary alloy system using lead salt stabilizer. On the whole, the modification effect of lead salt stabilizers is better than that of organotin stabilizers. Therefore, the author mainly studies the relative mechanical properties of PVC/CPVC alloy under the stabilization of lead salt stabilizers.

2.3 The influence of different fillers on the properties of PVC/CPVC binary alloy
Add 5 parts of talc, clay, sericite, diatomaceous earth and active CaCO3 to the system of (PVC): (CPVC)=70:30. The effect of different fillers on the performance of PVC/CPVC binary alloy is shown in Table 3. .

It can be seen from Table 3 that the tensile strength of the PVC/CPVC alloy system is larger when using diatomaceous earth and active CaCO3, which are 47.9 MPa and 47.7 MPa, respectively. The impact strength is larger when using active CaCO~ and clay. They are 14.4 kJ/m2 and 12.2 kJ/m2 respectively. When using active CaCO3, the elongation at break of the sample also reached the maximum, which was 46.7%. Due to the small amount of filler used, the type of filler has little effect on the bending strength and thermal deformation temperature of the PVC/CPVC alloy system.
Comprehensive analysis of the experimental results can be seen: in the PVC/CPVC alloy system, the best choice of filler is active CaCO3.

2.4 Under the action of lead salt stabilizer, the morphology of the cross section of PVC/CPVC alloy impact samples of different fillers, m(PVC): m(CPVC)=70:30, choose B-564 as impact modifier, observe and add The microstructure of PVC/CPVC alloy system with different fillers such as talc, clay, mica, silica, CaCO, etc. under the electron scanning electron microscope.

Figure 2 lists the SEM pictures magnified 1,500 times and 10,000 times.

Comparing the SEM photos of a～e after magnified 1500 times in Fig. 2, active CaCO3 and silica have good compatibility with the organic system, and the dispersion is even; while the dispersion of talc, clay, and mica in the system is not uniform. The compatibility of the system is not good, with particles falling off and voids. The above-mentioned situation can be observed more clearly in the SEM photos of a to e at 10,000 times magnification in Figure 2. Since silica is an organic filler, it is helpful to improve the yield strength, tensile strength, bending strength and breaking strength of the material, but it cannot improve the impact performance of the material; CaCO3 filler can play its toughening effect well. Greatly improve the impact performance of the material.

2.5 The effect of filler content on the properties of PVC/CPVC alloy
In the PVC/CPVC alloy system, add 5-20 parts of active CaCO3, respectively, and examine the effect of its dosage on the performance of the PVC/CPVC alloy. The results are shown in Table 4.

With CaCO. With the increase of the amount, the tensile strength, bending strength, and elongation at break of PVC/CPVC alloy showed a trend of first rising and then falling. The three reached the maximum after adding 5 parts of active CaCO3, and then began to decrease as the amount of active CaCO3 continued to increase. When the amount of active CaCO3 reaches 20 parts, the three are respectively 81%, 84% and 69% of the maximum value. The impact strength of the system fluctuates up and down with the increase in the amount of active CaCO3, but it is basically maintained at about 13 kJ/m2. The heat distortion temperature does not change much when the amount of active CaCO3 is 5 to 15 parts, but when the amount of active CaCO3 exceeds 10 parts, the heat distortion temperature rises.

Table 4 The influence of CaCO dosage on the properties of PVC/CPVC alloy

Basic formula: PVC/CPVC 1O0, 3PbO 3, 2PbO 3, BaSt2 1.5, KM355P 8, K1 25P 2, filler 9, lubricant 0 7.

3 Conclusion
(1) CPVC is prone to HCL removal reaction during processing. Commonly used lead salt stabilizers and organotin stabilizers for PVC are all suitable for CPVC system, and the stabilizing effect of lead salt stabilizers is better than that of organotin stabilizers.
(2) When m(PVC):m(CPVC) changes from 1O0:0 to 70:30, as the amount of CPVC increases, the yield strength, tensile strength, flexural strength, and thermal strength of the PVC/CPVC binary alloy system The deformation temperature (maximum bending normal stress is 1.82 MPa and 0.45 MPa, respectively) shows an increasing trend, while the impact strength and elongation at break show a decreasing trend, especially with the increase of the CPVC content, the PVC/CPVC binary alloy system The elongation at break has dropped significantly.
(3) When the amount of filler is 5 parts, the tensile strength of the PVC/CPVC alloy system is greater when diatomaceous earth and active CaCO3 are selected, and the impact strength is greater when active CaCO3 and clay are selected. Due to the small amount of filler, the filler has little effect on the bending strength and thermal deformation temperature of the PVC/CPVC alloy system.
(4) As the amount of CaCO3 increases, the tensile strength, flexural strength and elongation at break of PVC/CPVC alloys generally increase first and then decrease. The change of active CaCO3 dosage has almost no effect on impact strength. The heat distortion temperature does not change much when the amount of active CaCO3 is 5-15 parts, but when the amount of active CaCO3 exceeds 10 parts, the heat distortion temperature rises.

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