Chrome emblems-Of polypropylene (PP) modified the expected rate of contraction      Source: :Internet 

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Polypropylene is a common plastic in the amount of one of the larger species, the density of small, rigid, and bending resistance, corrosion-resistant chemical, the advantages of good insulation. It is the inadequacy of the poor performance of low-temperature impact, easy to aging, shrinkage of the molding. Modification of polypropylene can be improved through the low-temperature impact performance, molding shrinkage and thermal aging properties. The use of polypropylene so that the convergence of expansion, on many occasions to replace the traditional engineering plastics. Polypropylene adequate sources of raw materials, cheap, thus modified in recent years in the plastic industry occupy the first modified polypropylene, a plastic modified the main varieties, more and more people's attention.
     Polypropylene modified material shrinkage control of polypropylene is an important aspect of the modification. Shrinkage of the good control of polypropylene modified to promote the use of the material is important, but also guarantee product quality an important aspect. In particular the use of modified polypropylene replacing traditional engineering plastics, the shrinkage rate this point is very important.
PP has been modified in the domestic mature technology, the physical and chemical properties of polypropylene modified also a lot of research reports, but the shrinkage problem is very few specialized reports. I set many years of practical experience on the modified polypropylene material control the rate of contraction has done some of the problem.
1. Test of the
1.1 testing of raw materials
Polypropylene (PP) Liaoyang Petroleum Chemical Fiber Corporation; high-density polyethylene (HDPE) Liaoyang Petroleum Chemical Fiber Corporation
POE U.S. DuPont; EPDM Dutch company DSM; SBS Yueyang Petrochemical Plant
Shanghai Yaohua Glass; Yingkou Dashiqiao calcium carbonate, talc Haicheng the new
Mica Powder Hebei; commercial additives; low-density polyethylene (LDPE) Yanshan Petrochemical
1.2 test equipment and apparatus
Extruder TM40MVC/D-40 Italy MARIS; injection molding machine TP120T Beijing letter crown Machinery Manufacturing Co., Ltd.
Melt Index-μ PXRZ-400C Jilin University science and education Instrument Factory; caliper; detection method: ASTM D955
1.3 sample preparation and detection method
     Raw materials mixed ---- ---- extrusion granulation injection proofing (at 24 h )---- detection rate of contraction (ambient temperature of 23 ℃)
Injection conditions: temperature of 170 ℃ --- 190 ℃ pressure 80
2. Outcome of discussions
      Polypropylene is a contraction of polypropylene molding itself a major drawback, it is mainly because of the high degree of crystallinity polypropylene result. After the crystallization of the increasing proportion of polypropylene, volume shrinking. Crystallinity of 0% and 100% of its share of 0.851 and 0.936 respectively. So pure PP molding contraction in general between 1.7 --- 2.2. Control of polypropylene molding shrinkage is mainly to control its raw materials forming the crystallization: crystallization of its smaller contraction rate of forming the smaller the contrary, the higher the degree of crystallization of the molding greater the rate of contraction.
In the modified polypropylene plastic, because of the variety of agents have joined the different levels of destruction of the original crystalline polypropylene, which changed the original molding polypropylene shrinkage.
2.1 rubber on the rate of contraction of polypropylene
     Shown in Figure 1 on the PP modified rubber molding material impact on the rate of contraction. As can be seen from the map with the increase in rubber, forming a declining trend rate of contraction. This was mainly due to the rubber by adding self-destruction of the crystallization of the PP, leading to shrinkage of forming the decline, but three elastomer POE, EPDM, SBS impact on molding shrinkage There are also differences.
a: POE b: EPDM c: SBS a: talc b: CaCO3 c: Mica Powder
2.2 mineral filled polypropylene modified material forming the rate of contraction
      Polypropylene used in mineral filled with PPD mainly calcium carbonate, talc, Mica Powder, and so on. Various mineral filled polypropylene with PPD on the rate of contraction forming shown in Figure 2, can be seen from the map minerals on the PP filled with PPD modified material forming contraction rate of more obvious. Mineral filled with PPD modified polypropylene materials forming the shrinkage rate of three main aspects: First, mineral filled with PPD do not shrink, its accession to the overall proportion of polypropylene modified to reduce the expected rate of contraction; The second is the addition of mineral filled with PPD will definitely affect the crystallization of polypropylene, thus affecting the rate of contraction; third is fine after the entry of minerals, played a role in nucleating agent, to change the structure of the state of polypropylene, The big crystal ball-the formation, the impact polypropylene molding shrinkage.
2.3 on the polypropylene fiber glass forming modified material impact on the rate of contraction
     Modification of polypropylene fiber glass materials forming the largest rate of contraction. As shown in Figure 3, when the glass fiber content of more than 30%, its modified polypropylene materials forming the shrinkage rate dropped from 1.8 to 0.5, and the surface treatment of glass forming the contraction rate of not more than To deal with the fiberglass. The addition of a glass fiber undermine the crystallization of polypropylene, the impact of shrinkage is more important to limit the polypropylene fiber glass the crystallization of contraction.
                a: untreated surface b: surface treatment a: LDPE b: HDPE
2.4 The addition of polyethylene polypropylene molding rate of contraction
     Shown in Figure 4 for polyethylene joined in the molding of polypropylene and impact of shrinkage. As can be seen from the map of polyethylene joined modified polypropylene materials have also affected the molding shrinkage. While polyethylene is also a high degree of crystallization of the plastic, forming shrinkage also great, but after joining the PP in each other are different degrees of damage to their crystalline, so that the overall rate of decline in molding contraction.
MFI 2.5 polypropylene own change on forming the rate of contraction
    PP molding shrinkage by crystallization of the impact, and the crystallization of its molecular weight and size by the impact. When the MFI increases, molecular weight decreases, the crystallization rate of increase, forming shrinkage rate increases. Figure 5 shows the change in the MFI polypropylene molding rate of contraction.
Several modifier of 2.6 polypropylene molding shrinkage of comparison
     Various modifiers modified polypropylene materials forming the rate of contraction as shown in table 1, can be seen from the table in various modifiers of polypropylene modified material forming rate of contraction is different, Fiberglass most affected.
    Polypropylene modified material forming the shrinkage due to join the modifier not the same, forming shrinkage is not the same. During the trial, we found that several modifier and results when it does not use the same impact on many factors. If modifier in the dispersion of polypropylene, mineral modifier own size, all kinds of minerals filling the surface with PPD, and so on, all have an impact on molding shrinkage. In addition, in the process of injection molding machine molding process on the molding rate of contraction is also great. Such as the injection temperature and pressure changes on the injection molding shrinkage rate impact.

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www.dlysport.com  2008-10-29 13:59:16