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Among the five general-purpose plastics, the development history of polypropylene (PP) is short, but it is the fastest growing one. Compared with other general-purpose plastics, PP has better comprehensive performance, such as: Relative density is small, and it has better resistance. Heat, Vicat softening point higher than HDPE and ABS, excellent processing performance; mechanical properties such as yield strength, tensile strength and elastic modulus are higher, rigidity and wear resistance are superior; have a smaller dielectric rate, Good electrical insulation, resistance to stress cracking and chemical resistance, etc. However, due to PP molding shrinkage rate, high brittleness, low notch impact strength, especially at low temperatures is particularly serious, which greatly limits the promotion of PP and Application. For this reason, from the mid-1970s, a great deal of research on PP modification was carried out at home and abroad. Especially in improving the notched impact strength and low temperature toughness of PP, it has become a focus and hotspot at home and abroad.
1 Rubber toughened PP
Rubber or thermoplastic elastomer toughened plastics with a dispersion of elastomeric particulates has proven to be a toughening effect. Since PP has a large number of crystal grains, the spherulite interface is prone to cracking during processing. Its brittleness. Through incorporation of various rubbers 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 tougheners are EPDM rubber (EPDM). Propylene rubber (EPR), styrene and butadiene thermoplastic elastomer (SBS), butadiene rubber (BR), styrene-butadiene rubber (SBR), etc., with EPDM or EPR taking the best effect.
1.1 PP/EPB rubber blending system
PP and ethylene-propylene rubber both contain propyl groups and their solubility parameters are similar. According to the similar compatibility principle, they should have good compatibility. Because ethylene-propylene rubber has high elasticity and good low-temperature performance, it shares the same with PP. Blending can improve the impact properties and low temperature brittleness of PP.
Li Yuneng et al studied the properties of ethylene propylene rubber core P blends, and concluded that the toughening of copolymerized PP is much better than toughening homopolymer PP at the same rubber content, and the toughening effect is related to the type of rubber. Under normal circumstances, EPR toughening effect is better than EPDM. Through experiments found that when the rubber content is 30%, the toughening effect is the best; different crystallinity of the EPR toughening effect of PP is not the same, the lower the crystallinity The better the toughening effect.
Liu Xiaohui et al. studied the mechanical properties of Pr)M blends with different PP centers. The results showed that: (1) With the increase of the amount of EPDM in the system, the impact strength of the material increased significantly, when the EPDM content was about 30%. (2) The impact strength increases and changes 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 the crystal structure of the mechanical properties Does not work.
If peroxides and auxiliaries are added to the system of PP and rubber, they can be dynamically vulcanized and blended to achieve the ideal blending effect. First, reactive extrusion technology is used, and second, suitable peroxides and additives are selected. System. Since the dynamic vulcanization process has both the cross-linking of the rubber components and a small amount of rubber is grafted onto the PP main chain, it has better dispersion in the PP matrix, and the interface between the two polymers can also be achieved. Big bond strength.
Dendrobium and others used diphenyl methane type bismaleimide (BMI) as a cross-linking agent and dicumyl peroxide (DCP) as a cross-linking initiator to carry out vulcanization experiments on an open mill to investigate the dynamics of EPDM. The mechanical properties of vulcanized toughened PP. The experiment shows that when the vulcanization system is 0y with MI=0.20:1, the curing temperature is 175-180°C, and the vulcanization time is 14min, the impact strength is the highest, reaching 157kJ/m. The tensile strength (39.0 MPa) and 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 toughening of EPDM is better than that of pure EPDM. , can effectively improve the toughness of PP.
Gu Fangming et al studied the effect of adding HDPE and various processing aids on the properties of PP/EPDM blends. The results show that the controllable degradation of PP in the presence of peroxide is an effective means to improve the fluidity of the blends. However, the impact toughness significantly decreased. HDPE and processing lubricants can be adjusted to adjust the fluidity of the blend, and the use of controlled degradation and dynamic cross-linking technology, can obtain high toughness, high flow toughening PP.
1.2 PP / butadiene rubber blending system Wang Li used simple blending and dynamic vulcanization blending two processes PP / BR blends were prepared, the impact strength of the two blends at room temperature and low temperature were measured. The results show that The dynamic vulcanization method can reduce the PP spherulite size, increase the uniformity of PP spherulite distribution, improve the morphological structure 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 blend system Using vulcanized powder rubber to blend and toughen modified PP, it not only improves the impact performance of PP blended materials, but also reduces the cost. Recently, Tao Guoliang et al. vulcanized rubber powder/PP The blends were studied using the following process routes: powder handling - raw material mixing - two-roll mixing - comminution - injection test - performance tests, and concluded that: (1) vulcanized rubber powder can improve the resistance of PP materials Impact performance, and the smaller the particle size of the rubber powder, the better the effect, but will make the blended system tensile strength bridging down. When the rubber powder content is 5% -15%, the overall performance of the blending system is better; 2) Adding a coupling agent to the vulcanized rubber powder/PP system will improve the mechanical properties and heat distortion temperature of the blend; (3) The increase in the content of the vulcanized rubber powder will decrease the flowability of the blend system, but the rubber powder The smaller the particle size is, the more beneficial it is to reduce the flow resistance of the blend. If the vulcanized rubber powder/PP blend material can be widely applied, it can contribute to the recycling and environmental protection of used 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. Because TPI has strong crystallinity (Tm =70°C) Similar to plastic at room temperature, it is a hard material and it is difficult to be recognized and applied by people. China has taken the lead in discovering the vulcanization and crosslinking system of TPI vulcanized into an elastomer, and its mechanical properties are better than natural rubber. Peng Shaoxian It was found that the uncross-linked hard TPI can be broken, extruded, granulated, and blended with PP using a general-purpose plastic machine. After dynamic vulcanization, it has a good toughening effect.
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