Research progress on polypropylene modification technology
Among the five general-purpose plastics, polypropylene (PP) has a short history, but it is the fastest growing one. Compared with other general-purpose plastics, PP has better comprehensive properties, such as: relatively low density and good resistance. Thermal, Vicat softening point is higher than HDPE and ABS, excellent processing performance; mechanical properties such as yield strength, tensile strength and elastic modulus are high, rigidity and wear resistance are excellent; with a small dielectric ratio, Good electrical insulation, stress crack resistance and chemical resistance, etc. However, due to PP molding shrinkage, high brittleness, low notched impact strength, especially at low temperatures, which greatly limits the promotion of PP and Application. For this reason, from the mid-1970s, a lot of research on PP modification has been carried out at home and abroad, especially in improving the notched impact strength and low temperature toughness of PP, which has become the focus and hotspot of research at home and abroad. Off Shoulder Short Sleeve,Ladies Plus Size Top,Printed Stripe Plus Size Blouse,Plus Size Causal Blouse SHAOXING ZHENNIU TRADING CO.,LTD , https://www.zhenniuclothes.com
1 Rubber toughened PP
Rubber or thermoplastic elastomers have toughened plastics with elastic particulate dispersion structure, which has been proved to be a more obvious method of toughening. Since PP has large crystal grains, cracks are likely to occur at the spheroidal interface during processing, resulting in cracks. Its brittleness. By blending various rubber or elastomers containing flexible polymer chains, the impact strength of PP can be greatly improved and the low temperature toughness can be improved. The traditional PP toughening agent is EPDM, binary B. Propylene rubber (EPR), styrene and butadiene thermoplastic elastomer (SBS), butadiene rubber (BR), styrene butadiene rubber (SBR), etc., of which EPDM or EPR takes the best effect.
1.1 PP/ethylene propylene rubber blend system
Both PP and ethylene propylene rubber contain propyl, and the solubility parameters are similar. According to the similar compatibility principle, they should have good compatibility. Because of the high elasticity and good low temperature performance of ethylene propylene rubber, it is shared with PP. Mixing can improve the impact properties and low temperature brittleness of PP.
Li Yunneng et al. studied the properties of ethylene-propylene rubber P blends and concluded that the toughening copolymer PP is much better than toughened homopolymer PP at the same rubber content, and the toughening effect is related to the rubber type. Under normal circumstances, the toughening effect of EPR is better than that of EPDM. It is found through experiments that the toughening effect is best when the rubber content is 30%; the toughening effect of PP with different crystallinity is different for PP, and the lower the crystallinity The better the toughening effect.
Liu Xiaohui et al. studied the mechanical properties of different PP core Pr)M blends. The results show that: (1) With the increase of EPDM in the system, the impact strength of the material increases obviously, when the EPDM content is about 30%. The impact strength has an extreme value; (2) the increase and change of impact strength are related to the morphology and distribution of EPDM in PP; (3) the addition of EPDM has an effect on the crystal structure of the blend, but the difference in crystal structure is related to the mechanical properties. Does not work.
If peroxide and additives are added to the PP and rubber system, it can be dynamically vulcanized and blended to achieve the desired blending effect. First, reactive extrusion technology is used, and second, suitable peroxides and additives are selected. System. Because the dynamic vulcanization process has the cross-linking of rubber components, and a small amount of rubber is connected to the PP main chain, so that it has better dispersibility in the PP matrix, the two polymer interfaces can also achieve Large bonding strength.
Shiqi et al. used diphenylmethane-type bismaleimide (BMI) as a cross-linking agent, dicumyl peroxide (DCP) as a cross-linking initiator, and a vulcanization experiment on an open mill to explore EPDM dynamics. The mechanical properties of vulcanized toughened PP. The experiment shows that when the vulcanization system is 0y with MI=0.20:1, the vulcanization temperature is 175-180°C, and the vulcanization time is 14min, the impact strength is the highest, up to 157kJ/m. The tensile strength (39.0MPa), the elongation at break (451%) reached the highest value, and the permanent deformation rate (13.6%) was the lowest. It can be seen that the dynamic vulcanized EPDM has better toughening effect than the simple EPDM. Can effectively improve the toughness of PP.
Gu Fangming et al studied the effect of adding HDPE and various processing aids on PP/EPDM blends on the properties of the materials. The results show that the controlled degradation of PP in the presence of peroxides is an effective means to improve the fluidity of the blends. However, the impact toughness is significantly reduced. The addition of HDPE and processing lubricants can properly adjust the fluidity of the blend, and the combination of controlled degradation and dynamic crosslinking can achieve high toughness and high fluidity toughening PP.
1.2 PP/butadiene rubber blending system Wang Li used PP and BR blends by simple blending and dynamic vulcanization blending to determine the impact strength of the two blends at room temperature and low temperature. Dynamic vulcanization can reduce PP spherulite size, increase the uniformity of PP spherulite distribution, improve the morphology of the blend, increase the compatibility of the two phases, and effectively improve the low temperature impact strength of the blend.
1.3 PP/vulcanized rubber powder blending system The blending and toughening modification of PP by vulcanized powder rubber not only improves the impact properties of PP blending materials, but also reduces the cost. Recently, Tao Guoliang and other vulcanized rubber powder/PP The blend was studied and the process route was: rubber powder treatment - raw material blending - twin roll mixing - crushing - injection sample - performance test, and concluded that: (1) vulcanized rubber powder can improve the resistance of PP material Impact performance, and the smaller the particle size of the rubber powder, the better the effect, but the tensile strength of the blend system will decrease. When the rubber powder content is 5%-15%, the comprehensive performance of the blend system is better; 2) Adding a coupling agent to the vulcanized rubber powder/PP system is beneficial to improve the mechanical properties and heat distortion temperature of the blend; (3) The increase of the vulcanized rubber powder content will reduce the flow properties of the blend system, but the rubber powder The smaller the particle size, the better the flow resistance of the blend is reduced. If the vulcanized rubber powder/PP blend material can be popularized and applied, it can contribute to the recycling and environmental protection of waste tires and rubber products in China.
1.4 PP / eucommia rubber blend system The main component of gutta-percha is trans-1,4-polyisoprene (TPI), which is an isomer of natural rubber. Due to the strong crystallinity of TPI (Tm =70 ° C), similar to plastic at room temperature, is a hard material, so it is difficult to be recognized and applied. China has first discovered that TPI vulcanization is an elastomeric vulcanization cross-linking system, and some of its mechanical properties are superior to natural rubber. Peng Shaoxian It was found that the uncrosslinked hard TPI can be crushed, extruded, granulated, blended with PP by general plastic machinery, and has better toughening effect after dynamic vulcanization.