Mechanism and Application of Polypropylene modified by Thermoplastic Elastomer

Polypropylene (PP) has many advantages such as high tensile strength, high yield strength, high hardness, high hot deformation temperature and low price. It is widely used in daily necessities, automobile parts and other fields. However, PP has high shrinkage, high brittleness and low notched impact strength, especially at low temperature, which greatly limits the popularization and application of PP.

 

Thermoplastic elastomer (TPE) is a kind of polymer material with physical properties between rubber and plastics. It can be used in the modification of general thermoplastic resins such as polyvinyl chloride (PVC), polyethylene (PE), polypropylene (PP) and engineering plastics such as polyurethane (PU),) polyamide (PA) instead of rubber.

 

Classification of TPE and its mechanism of toughening PP

 

It can be divided into polyurethane TPE (TPU),  TPE (TPS),  TPE (TPO), etc. according to their structural characteristics .TPU has excellent elasticity, wear resistance, oil resistance and low temperature mechanical properties; TPO has heat resistance, cold resistance, weather resistance and reproducibility; TPS has rubber elasticity and low temperature resistance.

 

Mechanism of toughening PP by Elastomer:

On the one hand, the toughness of the elastomer is higher than that of the PP resin. When the elastomer is distributed in the continuous phase of PP as the dispersed phase, the "sea-island" structure is formed, and when the blend is subjected to external force, the elastomer particle acts as the stress concentration point. If the interface between the two phases is bonded well, it will result in a large amount of craze and shear band in the region where the particles are located and consume energy. At the same time, the elastomer particles can block, turn and stop the development of small cracks. Increase the toughness of the system;

On the other hand, the addition of elastomer destroys the crystallization of PP, makes the spherulite of PP refined, and the elastomer plays the role of heterogeneous nucleation and thus plays a toughening role.

 

Application of TPE in PP Modification

 

TPO modified PP

TPO, which is often used in PP modification, is a kind of ethylene-octene copolymer (POE) Poe, which has good compatibility with PP, and can be dispersed in PP, and the production cost of POE is lower, and POE is often used as the modifier of PP.

 

TPS modified PP

Styrene thermoplastic elastomers can be divided into SBS, SIS, SEBS and so on. SBS、SEBS are commonly used for PP modification.

 

SEBS modified PP

SEBS has better stability, heat resistance and oxidation resistance than SBS. It has good fluidity and can be used as compatibilizer of PP and reinforced material to obtain good properties.

 

TPU modified PP

Blending of TPU and PP can improve the toughness of PP, such as easy stress cracking and notch sensitivity, improve the abrasion resistance and oil resistance of PP, and reduce the processing temperature of PP. However, the stiffness and hardness of TPU are low, the price is high and the compatibility with PP is poor, so it is not a common modifier for PP.

In order to obtain good toughening effect, a large number of TPE are usually added, but the rigidity and strength properties of PP matrix will be lost.