Crosslinked polystyrene (PS) particles in latex form were synthesized by free-radical emulsion polymerization. The nano-PS filled elastomer composites were prepared by the energy-saving latex compounding method. The results showed that the PS particles took a spherical shape in the size of 40 to 60 nm with a narrow size distribution, and the glass transition temperature of the PS nanoparticles increased with the crosslinking density.
The mechanical property results demonstrated that when introduced into styrene-butadiene rubber (SBR), nitrile-butadiene rubber (NBR), and natural rubber (NR), cross-linked PS nanoparticles exhibit excellent reinforcement capabilities in all three matrices. , and the best in the SBR matrix. Compared to carbon black filled composites, another prominent advantage of crosslinked PS particulate filled elastomeric composites was found to be light density, which could help save a huge amount of energy when placed in final products.
Styrene (St) was purchased from Fuchen Chemical Agent Co., Ltd (Tianjin). Divinylbenzene (DVB) was supplied by Jinke Fine Chemical Agent (Tianjin) Co., Ltd. and sodium hydrogen carbonate (NaHCO3) was supplied by Shanghai Linfeng Chemical Agent Co., Ltd., China. Ammonium persulfate (APS) was purchased from Beijing Chemical Agent Co., Ltd., China. Polyoxyethylene octylphenol ether (OP-10 emulsifier) was supplied by Vason Chemical Agent Co., Ltd (Tianjin).
Sodium dodecyl sulfonate (SDS) was a commercial product of Beijing Yili Fine Chemical Co., Ltd. Anhydrous calcium chloride (CaCl2) was a product of Beijing Beihua Fine Chemicals Co., Ltd. Styrene-butadiene rubber (brand of manufacture SBR-1502), and its latex was supplied by Jilin petrochemical Co. China. Nitrile-butadiene rubber latex (brand name LHN-212), with an acrylonitrile content of 26% by weight, was a product of Lanzhou petrochemical Co. China. The natural rubber latex was purchased from the latex factory in Beijing, China. All other reagents for rubber compounds are commercial products.
2.2. Synthesis of cross-linked polystyrene
A four-necked flask equipped with a stirrer, a reflux condenser, a dropping funnel, and a thermometer, was first charged with the appropriate SDS / OP-10 emulsifier and deionized water. Run the agitator at a suitable speed for a while until a uniform mixture is obtained. The batch was then charged with a certain amount of DVB and styrene monomers in a specified ratio. After another 30 minute emulsion, the batch was heated.
When the temperature stabilized, the polymerization was started by adding an APS water solution. An aqueous solution of NaHCO3 was added to adjust the pH value of the latex equal to 7. The temperature of the batch was maintained throughout the polymerization process. The remaining monomers had been added dropwise from 30 minutes after initiation. Several hours later, the emulsion polymerization reaction was completed. And the cross-linked polystyrene latex was obtained.
2.3. Preparation of filled composites
The PS-filled elastomeric compounds were prepared by LCM. The cross-linked polystyrene latex and rubber latex were mixed in a certain proportion by a mechanical stirrer for a period of time. After that, the uniform mixture was poured into the aqueous CaCl2 solution with stirring for coagulation. The masterbatch was washed several times before drying in an air oven for 24 hours. All the curative ingredients (seen in Tables 1 and 2) were added to a two-roll grinder. The masterbatch was then vulcanized at a certain temperature (for SBR, for NBR, and for NR) for a period of time at a pressure of 15 MPa.
The cross-linked polystyrene was prepared by free-radical emulsion polymerization; the PS particles took on a spherical shape of the size of 40 to 60 nm with a narrow distribution. The crosslinked PS particles exhibited excellent polar and apolar elastomeric matrix reinforcement, such as SBR, NBR, and NR. But the tensile strength of the PS-filled NR nanocomposites deteriorated somewhat. With the increase of the filler load, the mechanical properties of the composites improved remarkably.
Particularly in the SBR matrix, the cross-linked polystyrene particles had good compatibility and strong interactions with the rubber matrix, which resulted in a dramatic improvement in mechanical properties. With increasing crosslink density, the spherical cross-linked PS particles were given a higher glass transition temperature and thus the ability for hot environment applications, but less stability in the radical polymerization system in the emulsion.
In the compounds, the filler-rubber interactions of the PS-filled SBR compounds weakened with crosslinking density; however, in the high-temperature sulfur vulcanization system, the interactions between the filler and the rubber improved after heating. As a distinctive advantage of polymeric fillers, elastomeric composites filled with crosslinked PS particles were superior to conventional fillers in weight and density.