Pvc Resin has the advantages of flame retardancy, wear resistance and chemical resistance. Polyvinyl chloride and its alloy products can be classified into hard products and soft products according to the amount of plasticizer added. Soft products add a certain amount of plasticizer to the polymer, reduce the force between the polymer molecules, increase the mobility of the molecular chain, reduce the glass transition temperature, and improve the low temperature processing performance. DOP is one of the main plasticizers for soft PVC products .
Due to the excellent characteristics of PVC, such as high impact resistance, heat resistance, dimensional stability and easy processing and forming, the use of aBS for PVC blending modification Rubber And Plastic can not only improve the processing properties of PVC, but also significantly Improve the mechanical properties of PVC so that the impact strength of aBS/PVC blends exceeds that of pure aBS and PVC [2, 4]. PVC/aBS blends are an important modified plastic. This experiment comprehensively analyzed the effect of DOP on the mechanical properties and hardness of pure PVC and PVC/aBS blends.
1 experimental part
1.1 Experimental materials
Polyvinyl chloride (PVC), SG-3, SG-5, Xinjiang Petrochemical Company; acrylonitrile/butadiene/styrene copolymer (aBS), Pa-747S, Taiwan Chimei Chemical Company; dioctyl phthalate (DOP), industrial grade,Sodium Hexametaphosphate commercially available; stabilizers, processing aids, etc. are domestic industrial grade.
1.2 Experimental instruments and equipment
Two-roller refining machine, SK-160B, Shanghai Rubber Machinery Factory; electronic tensile testing machine, aI-7000M, high-speed rail technology company rubber hardness tester, Shaw a, Shanghai Xianfeng Film Machinery Factory.
1.3 Experimental techniques and methods
1.3.1 Premixing of raw materials
According to the principle of segmentation and division, PVC resin, plasticizer, stabilizer, etc. are added first. After fully kneading and the plasticizer is completely absorbed, the dried aBS (baked at 120 ° C for 5 h) is added and kneaded to complete the material. Mix well.
1.3.2 Forming and sample preparation
The temperature of the two-roll mill is raised to 170 ~ 175 ° C, the mixed raw materials are added, and the mixture is mixed for 3 to 4 minutes to make the thin pass (thin pass refers to the mixing of the roll pitch to a small condition to ensure the blend distribution. Uniform) Uniform, then widen the test piece for 1~2min, then thin through for 1~2min, and Titanium Dioxide finally widen the width of the material until the color is uniform and the surface is shiny. The whole process is about 6~10min.
The cut plastic piece is placed in a mold (mold temperature 185 ° C, molded pressure 10 MPa), preheated by pressure, exhausted three times, hot pressed for 10 min, cold Dop pressed for 10 min, and the test piece is prepared and cut into standard samples.
1.4 performance test standards
The tensile test is carried out according to the GB/T528-92 standard; the tear test is carried out according to the GB/T529-91 standard; the hardness test is carried out according to the GB531-92 standard.
2 results and discussion
2.1DOP content on the performance of pure PVC
DOP is commonly used in PVC soft products, so the role of DOP in pure PVC resin is analyzed first. The loose PVC powder produced by the suspension method is large, the surface is irregular, it is easy to absorb plasticizer, easy to plasticize, and the molding processability is good [3]; so the SG-3 and SG-5 two types of loose PVC are selected as experiments. Object. The effect of DOP content on tensile strength and tear strength of PVC is shown in Figures 1 and 2.
Figure 1
It can be seen from Fig. 1 and Fig. 2 that the tensile strength and tear strength of the system decrease with the increase of DOP content. The reason is that DOP is a medium viscosity liquid plasticizer with good compatibility with PVC, and its plasticized PVC resin has good viscosity stability. Structurally, DOP contains a benzene ring. When it is mixed with PVC at high temperature, DOP molecules are inserted into the PVC molecular chain. The ester-based dipole of DOP interacts with the dipole of PVC and polarizes the benzene ring of DOP. DOP and PVC molecular chains are well combined [1]. Since the methylene chain of the non-polarized portion of DOP is not polarized, it is sandwiched between the PVC molecular chains, increasing the distance between the chlorine atoms, weakening the interaction between the segments in the PVC molecule, which is equivalent to increasing the PVC. The length of the segment reduces the energy required to move the PVC segment. Therefore, as the amount of DOP is increased, the isolation is also increased, so that the tensile strength and the tear strength of the polymer are both lowered.
Figure III
From Fig. 3, as the amount of DOP increases, the change trend of the elongation at break of the system is different from that of Fig. 1 and Fig. 2. The elongation at break of the material decreases with the increase of DOP in the range of 20% to 30%, and the elongation at break increases with the increase of DOP content after more than 30%. This is because DOP reaches a certain concentration in the system and increases the relative motion between the polymer chains, reduces the crystallinity of the polymer chain, and improves the plasticity of the polymer material, resulting in an increase in elongation at break [5].
It can be seen from Fig. 1, Fig. 2 and Fig. 3 that the SG-3 type PVC resin is larger than the SG-5 type PVC resin in terms of tensile strength, tear strength and elongation at break. The reason is: in general, the greater the degree of polymerization, the better its tensile strength, compressive strength, modulus of elasticity, tear resistance, bending resistance, low temperature brittleness, heat aging, abrasion resistance, solvent resistance, etc. Compressive permanent deformation and good resilience, high strength and other characteristics of general rubber, therefore, PVC with a high degree of polymerization can prepare thermoplastic elastomers instead of ordinary rubber products, its wear resistance, colorability is better than rubber, and the price is low [ 5].
Figure 4
It can be seen from Fig. 4 that the hardness of PVC resin decreases with the increase of DOP dosage. The hardness of DOPSG-3 PVC resin is higher than that of DOPSG-5 PVC resin, which is the viscosity of SG-3 PVC resin. The reason for the large degree of polymerization also reflects the above principle regarding the relationship between the degree of polymerization of PVC and the properties.
Effect of 2.2DOP and aBS content on the properties of PVC/aBS blends
In summary, PVC/aBS blends have basically met the requirements of performance [6] when 40 or 50 parts of DOP were added. In the following experiments, we compared the effects of 40 parts and 50 parts of DOP on the properties of the blends, selected the best DOP dosage, and discussed the effect of aBS dosage on the material properties.
Effect of aBS dosage on material properties
It can be seen from Fig. 5 and Fig. 6 that the effect of the amount of DOP on the properties of the blend is similar to that of Fig. 1 to 3, that is, the stretching and tearing of the system with 40 parts of DOP compared with the system with 50 parts of DOP. The strength is high. In addition, after the addition of DOP, part of the DOP is dispersed on the PVC/aBS two-phase interface, which hinders the compatibility of the compatibilizer and reduces the bonding strength of the two-phase interface, which is also a reason for reducing the strength of the blend. When the content of aBS is small (0 to 50 parts), the negative effect of rubber phase butadiene with a small tensile strength in aBS on the tensile strength of the material is dominant, so it can be seen that with the increase of aBS, butadiene When the content is increased, the tensile strength and tear strength of the blend generally decrease.
As shown in Table 1, when the DOP was increased from 40 parts to 50 parts, the hardness of the material was lowered and the elongation at break was increased. The reason is that as DOP increases, its role in destroying interface compatibility and increasing polymer chain spacing is increasing. In addition, since the aBS material itself has small elongation at break and high hardness, as the amount of aBS increases, the elongation at break and hardness of the blend will show corresponding changes as shown in Table 1.
When PVC/aBS blending material is used to produce the skin of automobile instrument panel, it is considered that the skin vacuum adsorption molding process requires that the tensile strength is not broken (elongation at break >150%), and the tensile properties such as the use environment are higher. Performance (tensile strength 12 ~ 25MPa) [6]. Combined with the analysis of the experiments of 2.1 and 2.2, 40 parts of DOP with better comprehensive performance were selected as the basic formula of the experiment, and SG-3 type PVC with good fluidity and strong mechanical properties was selected as the experimental raw material.
3 conclusions
When the amount of DOP is more than 30%, with the increase of DOP dosage, the processability and elongation at break of the material are obviously improved in the pure PVC system. This is because when the content of DOP is high, the relative mobility between the polymer chains increases, the crystallinity of the polymer chain decreases, and the plasticity of the polymer material increases, resulting in an increase in elongation at break. At the same time, due to the addition of DOP, the distance between the polymer chains is increased, and the van der Waals force between them is weakened, so that the tensile strength, tear strength and hardness of the polymer are significantly reduced.
In PVC/aBS blends, when the aBS content is low (0 to 50 parts), some properties of the aBS material itself may have a certain negative impact on the corresponding properties of the PVC/aBS blend. The main performance is that as the content of aBS increases, the overall tensile strength, tear strength and elongation at break of the blend decrease, and the hardness slightly increases.
