Widely used thermoplastic plastic polypropylene (PP) is driven by its strong mechanical, chemical, and processing qualities. PP material itself has several restrictions, though, including low impact strength and brittleness, which somewhat limits its use in particular sectors. Researchers have worked extensively and improved PP using techniques like mixing modification to solve these flaws. There are two main methods for multi-componentization of PP, mainly simple mechanical blending and reactive blending.

Simple mechanical blending

PP and PE blending

Although the molecular structures of PP and PE are not very different, they are not completely compatible. The blend is still a two-phase structure, and their crystal structures have basically not changed, except that the crystal size of PP has decreased.
After PE is mixed with PP, the tensile strength is significantly reduced, but the impact strength is improved, especially the low-temperature toughness is greatly improved. For example, the blend of PP with 10%~40% HDPE can increase the drop ball impact strength by more than 8 times at -20C, and has good processing fluidity, which is suitable for injection molding of large containers.

The study concluded that within about 20% HDPE, the tensile strength and impact strength of PP/HDPE blends increase with the increase of HDPE content.

PP and EPDM blends

PP and EPRM (EPR) are similar in chemical structure, and the toughening effect of the blends is obvious, but the heat resistance and aging resistance are reduced.
Another EPDM (terpolymer composed of ethylene, propylene and diene) used for PP modification has a better toughening effect than EPR. 10%~15% EPDM can increase the unnotched impact strength of PP at -20℃ and -40℃ by 13 times and 17 times respectively.
PP/PE/EPR ternary blends have better comprehensive properties. It is a special structure with PP as the continuous phase and EPR rubber encapsulating PE microcrystals to form a dispersed phase, so it can play a better toughening effect.

PP blended with other rubber elastomers

PP is blended with butadiene rubber (BR) to achieve significant toughening effect.
The extrusion expansion ratio of PP/BR blends is smaller than that of PP, PP/LDPE, PP/EVA, PP/SBS and other blends, which means that after the product is processed and formed, it has good dimensional stability and is not easy to Warping deformation occurs.
PP/PE/BR ternary blends have also been used in industry to produce pipes that require good toughness and high tensile strength and flexural strength.

PP and random polypropylene blending

Arandom polypropylene (aPP) is a by-product produced in the production of polypropylene. It is a non-crystalline waxy viscous substance. This by-product cannot be made into products independently.
Blending aPP with general polypropylene resin can not only reduce the cost of polypropylene and make waste available, but also improve the impact toughness and processing fluidity of PP. A good blending effect can be obtained by general mixing methods. However, the rigidity and heat resistance of the blended modified PP are reduced.

Reactive blending

PP/PA blending system

PP is a non-polar polymer and is not thermodynamically compatible with highly polar nylon (PA).
Therefore, the thermodynamic compatibility of the material is poor when PP/PA is directly blended.
However, after maleic anhydride (MAH) is grafted onto the PP molecular chain to introduce anhydride or carboxyl groups, these active groups can react with -NH2 at the end of the PA molecular chain to achieve reactive compatibility (there is no terminal amino group on the PA66 molecular chain, and the acylamino group can be used for reaction).
Thereby improving the compatibility of high molecular multi-component polymers, improving the mechanical properties of multi-component polymer materials, and making them have higher use value.

PP/EPDM blend system

Using reactive compatibilizers to modify the PP/EPDM system, ultra-high impact PP blends can be obtained.
Since the compounds with functional groups form a partial cross-linked structure between the polyolefin molecular chains, the compatibility between the two phases is further improved. The resulting PP blend has high impact toughness and little decrease in tensile strength.
Many of the bumper materials currently used on cars are PP blends modified by this method.

COACE Conclusion

As an effective material modification method, polypropylene blending modification plays an important role in improving the performance of PP materials. Through continuous research and innovation, blending modification technology will inject new vitality into the development of polypropylene materials and promote its wide application in various fields.

COACE’S PP-g-MAH series products are maleic anhydride functionalized propylene polymers, which are mainly used in PP modification. Strong polar side groups (maleic anhydride) are introduced into the main chain of polypropylene, which can improve the interaction between polar materials and polar materials, and due to the interfacial adhesion of non-polar materials, it can improve their adhesion and compatibility.