Uncovering The Toughening Modification Formula of Polypropylene PP

The blending toughening of polypropylene PP is widely used in various fields due to its significant effects, low industrial investment, and fast and easy implementation. Blending toughening modification refers to the use of other plastics, elastomers, and inorganic powders as modifiers to blend with PP to improve the toughness of PP plastics. Common modification and toughening systems are mainly divided into the following types:

01 Plastic toughened PP system

Using other plastics as modifiers for PP toughening can not only achieve the goal of toughening, but also improve the physical properties of the material such as wear resistance and dyeing. When using general plastics such as polyethylene as modifiers, it also has a significant price advantage. The commonly used plastic products in PP toughening modification include HDPE and LLDPE EVA, PA, etc. However, due to its incompatibility with PP, it is often necessary to increase the dosage of modifiers or add compatibilizers to achieve high toughness in the system.

02 Rubber or thermoplastic elastomer toughened PP system

Blending rubber or thermoplastic elastomer with PP for toughening is currently a widely studied and effective method for toughening. This type of modifier mainly includes ethylene propylene diene rubber (EPR), ethylene propylene diene monomer (EPDM), styrene butadiene styrene block copolymer (SBS), butadiene rubber (BR), isobutylene rubber (IBR), natural rubber (NR), and polyolefin elastomers (such as POE). Different types of rubber can have a significant toughening effect on PP, but the toughening effect varies. There are many factors that affect the toughening effect of rubber, such as the content, size, and morphology of rubber particles, the interfacial adhesion and compatibility between rubber and PP matrix, rubber crosslinking, and rubber relaxation behavior.

03 PP/elastomer/plastic ternary blend system

The increase in the amount of elastomer significantly improves the impact performance of the system, but it brings losses in rigidity, strength, thermal deformation temperature, and flowability, and the cost also increases, resulting in limitations in practical applications.

Therefore, people are considering adding elastomers and plastics together to PP to form a ternary blend system to improve mechanical properties and reduce costs. The most common one is the addition of polyethylene (PE), which can be used as the main component in the system to form a mixed matrix with PP, or as a third component (toughening agent).

04 Inorganic Rigid Particle Toughening PP System

Elastomer toughened plastics have indeed achieved success in industry, but while improving toughness, they have significantly reduced stiffness, strength, and service temperature. In 1988, in the study of the fracture toughness of CaCO3 toughened PP composites, fracture mechanics was used to analyze the advancement of energy dissipation, and a new approach of filling reinforcement and toughening was first proposed in China. The commonly used inorganic rigid particles currently include CaCO3, BaSO4, kaolin, talc powder, mica, etc.

The mechanism of toughening polymers with inorganic rigid particles is not yet clear. It is generally believed that: 1. When the polymer undergoes deformation under force, the presence of rigid inorganic particles produces a stress concentration effect, causing the surrounding matrix to yield. This yield of the matrix will absorb a large amount of deformation work, resulting in toughening effects; 2. The presence of rigid inorganic particles can hinder crack propagation or passivate or terminate cracks. The reason for hindering crack propagation is due to the pinning effect, while the reason for particle passivation or terminating cracks is due to partial debonding at the two-phase interface.

According to the above mechanism, the requirement for achieving toughening is that the matrix should have appropriate toughness, and there should be moderate binding force between the matrix and particles, which inevitably requires appropriate active treatment of the surface of inorganic particles.

05 PP/Elastomer/Inorganic Particle Ternary Composite System

In order to balance the relationship between toughness and modulus, PP/elastomer/inorganic particle ternary composites have gradually gained the favor of researchers, such as PP/POE/BaSO4, PP/EPR/CaCO3, PP/EPDM/talc powder, PP/POE/CaCO3, etc. The use of elastomers and inorganic particles in this ternary system is also becoming increasingly diverse, opening up new avenues for further improving the comprehensive performance of PP and expanding its application fields.

The proposal of the ternary composite system is because when studying the interface bonding between inorganic particles and PP, it is considered that if an elastomer is introduced, it can not only serve as a third relative system for toughening, but also form an interface layer on the surface of inorganic particles, thereby overcoming stress concentration through shear deformation and preventing the detachment and crack development of inorganic particles and PP matrix.

The blending and toughening modification of polypropylene PP involves a complex and diverse variety of blending systems. It can be seen that using a single raw material as a toughening agent often cannot meet the high-performance requirements of plastic products.

Each toughening agent on the market has a different formula and ingredient ratio. At the same time, the dosage added varies depending on the performance of plastic particle raw materials. While meeting the performance requirements, it is also the pursuit of plastic manufacturing enterprises to minimize material costs. Therefore, choosing a high-performance and cost-effective toughening agent is particularly important.

NANJING HAISI is professional manufacturer of plastic extruder machine, we supply Twin Screw Extruder, Single Screw Extruder, Plastic Recycling Extruder, Two Stage Extruder, Lab Scale Machinery, Mixing and Feeding Machine, Cooling and Pelletizing Machine, Crushing Machine and so on.