11 schemes for PP toughening

1PP/PE Toughening system

Category	Characteristic
LDPE toughening	The toughening effect is obvious, and other mechanical properties such as the flexural modulus decrease rapidly. Therefore, it can only be used in applications where impact strength requirements are the main and other mechanical properties are not high.
HDPE toughening	When the amount of addition is less than 10%, it has a rigid toughening effect on PP, that is, while increasing the impact performance, other mechanical properties do not decrease.
LLDPE toughening	The toughening effect is between LDPE and HDPE, and the addition amount is 5%-20%.
UHMWPE toughening	It not only has a toughening effect, but also achieves an in-situ fiber-forming reinforcement effect. Taking PP1330 as an example, the notched impact strength, tensile strength and elongation increased by 3.5 times, 1.5 times and 2.5 times when 10% UHMWPE was added to toughen, respectively.

2PP/EVA Toughening system

While toughening PP, EVA can also improve elongation at break, melt flow index and surface gloss.

The content of VA in the selected EVA is between 14% and 18%. With 20% EVA-15 toughened PP, its impact strength is increased by 12 times, the rigidity reduction is small, and its cost is lower than that of elastomer or rubber toughened PP, and the comprehensive performance is better than that of PP/EPDM system.

3PP/PA6 Toughening system

PP/PA6 blending system can improve the inherent shortcomings of the two, so that the material has excellent comprehensive performance indicators, and selecting 15% PA6 into PP can increase its impact strength by 50% and reduce its tensile strength by 13.8%; If 5% PP-G-MAH is added as a compatibilizer, its impact strength can be increased by 113% and the tensile strength can be reduced by 2.7%.

 

4mPE/PP Toughening system

mPE has a very low glass transition temperature and large elongation at break, which is very suitable for toughening modification of PP.             

mPE has a good toughening effect on PP, and adding 40% mPE to PP, the notched impact strength at -30 °C exceeds 20 times that of pure PP, which is about 9 times that of EPDM with the same mass of parts. In addition, it is also found that with mPE toughened PP, the composite material has low tensile set, compression set and creep deformation, excellent low temperature performance and processing performance, and has become a strong competitor to EPDM.

In addition, the newly developed toughened material is ethylene-octene copolymer EOC, which can increase the impact strength of PP by up to 9 times.

5POE toughened PP system

PP/POE is an elastomer toughened PP system developed in recent years, which has the best toughening effect, good weather resistance, good fluidity, good thermal stability, good processing performance, and is also the most commonly used elastomer toughened PP system.

The compatibility between POE and PP is very good, the toughening effect, especially the low-temperature toughening effect, is very obvious, better than EPDM and EPR, and its toughening effect is POE>EPDM>EPR, and the flexural modulus and tensile strength decrease is small, and the descending order is POE<EPDM<EPR.

When POE is added to PP by more than 15%, the toughening effect increases rapidly. If 30% POE is added to PP, the notched impact strength increases from 76.4J/m of pure PP to 626J/m.

Compared with EPDM, POE has low cohesive energy, no double bonds, and good weather resistance, which is a powerful alternative to EPDM.

6 SBS toughened PP system  

SBS is not as good as EPDM toughening effect on PP, but can be used in general applications.

The results show that when the content of SBS is between 0-10 parts, the impact strength increases with the increase of the amount added. After more than 15 parts, the impact strength decreases. The impact performance of impact-resistant PP made of SBS and PP can be improved by 5 times and 10 times, respectively. When the specific formula is PP:SBS:CaCO3 =48:40:12, the impact strength of the cantilever beam with related properties is 70kj/m2.

7EPDM, EPR toughened PP system

EPDM (ethylene-propylene-diolefin terpolymer) and EPR (ethylene-propylene binary copolymer) are the most commonly used elastomer toughening materials in PP tradition, especially EPDM, both of which have high elasticity and good low temperature resistance, which can improve the impact performance and low temperature resistance of PP. Since both structures contain propyl groups, they have good compatibility with PP and very high thermal stability.

In the range of 5%-30% content, the impact strength of the system increases almost linear and rapidly with the increase of the amount added. But at the same time, the bending strength, tensile strength, heat deflection temperature, etc. of the system are significantly reduced.

Compared with EPR, EPDM and PP have good interface interaction, solubility parameters are equal (both 8.1), better compatibility with PP, and more obvious toughening effect on PP.

Taking EPR as an example, when 20% is added to PP, the impact strength of the notch at room temperature increases by as much as 10 times, and the embrittlement temperature decreases by as much as 4 times.

Taking EPDM as an example, when PP/EPDM/talc is used in a 100/20/10 ratio for automobile bumpers, the performance of different manufacturers is shown in the following table.

 

After the formation of EPDM-G-MAH after MAH grafting of EPDMM, PP toughened with EPDM-g-MAH has a better effect than pure EPDM.

8BR toughened PP system

Cis butadiene rubber (BR) has the advantages of high elasticity, good low temperature performance (glass transition temperature -110 °C), wear resistance, flex resistance, etc., and the solubility parameters of BR are close to PP, good compatibility with PP and good toughening effect.

When the PP/BR is 100/15, its impact strength is increased by nearly 6 times, and the embrittlement temperature drops to 8 °C (down 23 °C).

9Plastic/elastomer synergistic toughened PP system

Although the blend of elastomer and PP has excellent impact strength, the loss of rigidity, strength and heat deflection temperature is large, and the cost is significantly increased. In order to improve the mechanical properties and reduce costs, plastics are added to the elastomer/PP toughening system to form an elastomer/plastic/PP ternary blend.

The most commonly used plastics in ternary blending systems are HDPE and LLDPE, such as PP/SBS/HDPE, PP/EPR/HDPE, PP/EPDM/LLDPE, PP/HDPE/BR(100/15/15), PP/PS/mPE, PP/PS/SBS, etc.

PP/HDPE/BR ternary toughening system, when the ratio is 100/15/15, not only has good toughness, but also has high tensile strength and flexural strength.

The synergistic effect of PP/SBS/BR ternary blending system is significant, which is much better than that of single PP/SBS or PP/BR toughening effect.

 

The formulation design of the above toughening system should pay attention to the following points.

(1) Toughening effect. POE>mPE>TPE> EPDM, but economically consider that EPDM is more.

(2) Selection of compatibilizer. For toughened materials with poor compatibility with PP, compatibilizers should be added when formulating design, and PP-g-MAH is commonly used. After the addition of the compatibilizer, the impact strength increases significantly. Such as PA, PS, PVC, etc., all need to add compatibilizers.

(3) Determination of the amount of addition. Various toughened materials have an optimal addition range for the toughening effect of PP, such as SBS below 15% and POE above 15%.

(4) Selection of toughening materials. The toughening effect of different toughened materials and the impact on other properties are different, so the performance requirements of PP in different applications are also different, and toughened materials should be selected according to specific properties. If the aging resistance of EPR toughened PP is not good, the car bumper used outdoors generally does not choose EPR but EPDM with better weather resistance.

(5) Compound toughening. Single material toughened PP, although the impact strength is improved, but it has a greater impact on other properties. For this reason, compound toughening is often selected to balance all aspects of performance and reduce costs appropriately.

(6) The particle size of the elastomer. When the particle size is less than 1.5 microns, it can achieve better toughening effect.

10Inorganic rigid particle toughened PP system

Commonly used inorganic rigid toughening materials are mica, talc, wollastonite, calcium carbonate and barium sulfate.

After the pre-toughening system with rubber and the appropriate surface treatment of inorganic rigid particles, a core-shell dispersion structure with inorganic rigid particles as the core and rubber as the shell can be formed, and the toughening effect of inorganic rigid particles is very significant. Specific application examples include PP/EPDM/CaCO3, PP/EPDM/talc, PP/EPDM/wollastonite, etc.

The pre-toughening system without rubber has a large treatment strength for inorganic rigid particles, and it is best to add a coupling agent while adding a coupling agent, and the composite treatment effect is good. For inorganic rigid particles optimized by interface modifiers, shell-shell dispersion structures with inorganic rigid particles as the core and interface modifiers as the shell can also be formed. For example, PP/optimized kaolin toughening system, when kaolin is added 30%, the impact strength is as high as 480J/m; For another example, CaCO3 treated with alkyl carboxylate and coupling agent, when 50% is added to PP, its impact strength can be increased by about 1 times.

11Toughening of organic/inorganic nanomaterials

Nanomaterials are new materials just developed in the 80s of the 20th century, but also the most promising new materials in the 21st century, has received widespread attention, inorganic nanoparticles due to less surface defects, more unpaired atoms, large specific surface area, through the particle effect can improve the crystallization behavior of PP, crystal structure and the mechanical behavior of polypropylene in the interface area, so as to achieve the purpose of strengthening and toughening.