Do you know all eight key points for designing toughening formulations?

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(1) The compatibility between the elastomer and the resin should be good. ① Principle of similar polarity: The polarity of plastics ranges from cellulose plastics > PA > PF > EP > PVC > EVA > PS > PP, HDPE, LDPE, LLDPE. The polarity of elastomers increases in the order: rubber > nitrile rubber > neoprene rubber > styrene-butadiene rubber > cis-butadiene rubber > natural rubber > EPDM rubber. When making the selection, the polarity must correspond and match; that is, high-polarity resins should be paired with high-polarity elastomers, while low-polarity resins should be paired with low-polarity elastomers. ②The principle of similar solubility parameters: when making a selection, the difference in solubility parameters between the resin and the elastomer should be less than 1.5 to ensure good compatibility. (2) Addition of compatibilizers: In toughening systems where the compatibility between the resin and the elastomer is poor, appropriate compatibilizers should be added to improve their compatibility. Common compatibilizers are resin or toughener maleic anhydride or acrylic grafts. (3) Synergy of elastomers: The combined use of different types of elastomers often results in a synergistic effect; for example, in PP toughening formulations, the combined use of EPDM and ABS yields good toughening results. (4) Other factors to consider: Choose MBS when transparency of the product is required ； When the product requires flame retardancy, choose CPE; when the product needs weather resistance, choose CPE, ACR, and EVA – do not choose MBS or ABS ； When low production costs are required, CPE and EVA are chosen; the order of prices for different elastomers is MBS > ACR > ABS > NBR > CPE > EVA. (5) Rigidness compensation: When elastomers are used as toughening materials for resins, they enhance toughness but simultaneously cause a significant decrease in rigidness parameters such as tensile strength and flexural strength. To compensate for the loss of rigidity, rigid fillers such as calcium carbonate, talc, and mica powder need to be added to the formula ； Rigid organic resins such as AS and PMMA can also be added to the elastomer toughening system. (6) Amount of elastomer added: The more elastomer that is added, the better it is not – there is generally an optimal amount. When adding MBS to PVC, a maximum addition amount of 15% is applicable. (7) Co-addition of processing aids: In toughening formulations with high amounts of elastomers, except for ACR elastomers, all of them can increase the viscosity of the melt. To this end, lubricants or processing aids are generally added to improve their processability. (8) Particle size of the elastomer: The particle size of the elastomer has a significant impact on the toughening effect. According to the elastomer toughening theory, the particle size of brittle resins such as PS and PP can be relatively larger ； For resins with better toughness such as PVC, POM, PET, etc., the particle size of the elastomer can be relatively smaller. Furthermore, the particle size of the elastomer has a significant impact on the surface gloss of the product; the larger the particle size, the lower the gloss of the product. In HIPS, for example, the particle size of the elastomer is 2–5 microns, which results in a matting effect on the surface of the product; if the particle size of the elastomer is less than 0.5 microns, the surface of the product has better gloss.