HDPE (High Density Polyethylene) has low impact strength and is limited in its use. At present, it is often modified with a non-polar elastomer. Polar elastomer (NBR) nitrile silicone rubber contains polar group cyano group, which has excellent oil resistance, heat resistance, water resistance, etc., and has a large difference from HDPE solubility parameters. It is a thermodynamic incompatible system, but it is reasonable. The process conditions can make the process compatible. A small amount of NBR can greatly increase the impact strength of HDPE, and the phase structure is a filament arranged in parallel. Since HDPE and NBR are incompatible systems, it is necessary to add a compatibilizer. (Related products: thermoplastic EPDM rubber products)
HDPE/NBR binary blends and HDPE/NBR/HDPE-g-MAH ternary co-bentons were prepared by melt blending. The results showed that 15% NBR was added to binary blends with different polarities. A filamentary blend with an impact strength of 712.2 J/m and a parallel phase arrangement can be obtained; for a ternary blend system with a compatibilizer HDPE-g-MAH, the impact strength reaches 845.9 J/m, The toughening effect is improved after the compatibilizer. The HDPE part of the compatibilizer HDPE-g-MAH molecule is directly compatible with HDPE, and the MAH part contains a polar group carbonyl group, which chemically reacts with acrylonitrile in NBR to form a hydrogen bond. Since both ends are compatible with HDPE and NBR, it acts as an emulsifier, reduces phase interfacial force, increases the bonding force between the two phases, and forms a stable phase dispersion structure, so that the dispersed phase particles are dispersed continuously. In the phase, the compatibility of the two components is effectively improved, thereby improving the impact toughness. According to the analysis of compatibilizer compatibilization mechanism, the more the compatible dose is added, the better the modification effect should be, but the experiment proves that the modification effect is better when 10% compatibilizer is added instead of 5% compatibilizer. It may be because the compatibilizer is filled between the multi-phase interfaces of the blend system, so that the multi-phase interface macromolecular segments penetrate and diffuse through the compatibilizing effect, thereby reducing the interfacial energy and increasing the interphase force. The compatibilizing effect is best only when the compatibilizer is in the proper amount at the phase interface.
What is the blending modification of HDPE and NBR?
The modification effect of non-polar HDPE with polar NBR is related to the NBR grade and content and the melt flow rate of the matrix resin HDPE, and also related to the processing conditions such as mixing time, temperature and roll distance. At the beginning of the addition of NBR, the impact strength of the blend system increases linearly. When the content of NBR reaches a certain value, the impact strength reaches a maximum value. Thereafter, as the NBR content increases, the impact strength decreases. The modification effect of NBR-18 is better than that of NBR-26. According to the principle of "similar compatibility", the closer the polarity of the plastic phase to the silicone rubber phase, the better the compatibility. Therefore, HDPE/NBR-18 blends are more compatible than HDPE/NBR-26 blends. The order of HDPE modification effect of different grades is: 8900S>5000S>5070EA. The order of melt flow rate of the three grades of HDPE is: 5070EA>5000S>8900S.
The process conditions have a great influence on the impact strength. The mixing time is appropriate, the shear strength is appropriate, and the viscosity of the system can be close to the ideal viscosity point required for blending. When the mixing temperature is low, the dispersed phase and the continuous phase are difficult to disperse both macroscopically and microscopically due to the high viscosity of the melt, and it is difficult to achieve uniform mixing between the silicone rubber phase and the matrix resin; The viscosity of the melt is lowered, which also makes the difference between the dispersed phase and the continuous phase large, and the silicone rubber particles re-aggregate and the toughness is lowered. In addition, silicone rubber at high temperatures is also susceptible to oxidative degradation by hot air, which also affects performance. The size of the roll spacing reflects the shear strength. The larger the roll spacing, the smaller the shearing effect on the material. The smaller the roll spacing, the greater the shearing effect on the material. To some extent, the size of the roll spacing is consistent with the length of the mixing time. Related Process Recommendations: Advantages and Disadvantages of Various Silicone Rubber Rollers and Process Formula Introduction
The HDPE/NBR blend prepared by melt blending belongs to pseudoplastic fluid, and the viscosity shows a decrease with the increase of shear rate and temperature, and decreases with the decrease of NBR and compatibilizer content. Under different ratios, when T=190°C, when the NBR content is constant, its apparent viscosity increases with the increase of compatibilizer content. Because the compatibilizer has a certain physical and chemical interaction between the HDPE and NBR interfaces, the HDPE molecular chain and the NBR molecular chain are easy to form entanglement, which enhances the interaction between HDPE and NBR and hinders the molecular chain. Normal alignment results in increased resistance to movement of the blend melt during flow, resulting in an increase in the apparent viscosity of the blend.