In the world of rubber reinforcement, the quest for small particles, specifically around 2 μm or less, has been a longstanding challenge. The conventional size of starch granules exceeds this threshold, prompting scientists to explore innovative methods to shrink their dimensions and harness their potential in rubber compounds.
Unveiling Starch Xanthate’s Reinforcement Power
Buchanan et al. made a groundbreaking discovery with starch xanthate (SX), showcasing its prowess as a robust reinforcement agent for rubber compounds. By combining SX with elastomer latexes and zinc sulfate, they crafted a curd that, upon drying and milling, resulted in a fine particle dispersion of SX within the rubber compound. This notably enhanced the mechanical properties of carboxylic-modified and styrene-butadiene rubber, though natural rubber didn’t exhibit the same improvement. Intriguingly, exceeding 10 parts per hundred rubber (phr) of zinc SX accelerated the rubber’s curing process.
Exploring Commercial Viability: Stephens et al.’s Insights
Delving into the commercial potential of SX-reinforced rubber, Stephens et al. observed success with styrene-butadiene and nitrile-butadiene rubber but faced limitations with natural rubber. Their addition of 8% resorcinol-formaldehyde resin, based on the starch’s weight, proved beneficial for enhancing the mechanical properties across all three rubber compounds. Additionally, crosslinking SX with sodium nitrite yielded results akin to introducing the resin.
Powdered Compounds and Ethylene-Propylene Terpolymer Innovation
Buchanan et al. took their research further by creating powdered compounds using starch and flour xanthates, offering enhanced pigment accommodation. The process of milling or extruding these compounds before molding resulted in superior finished products. The team also pioneered xanthide-reinforced ethylene-propylene terpolymer compounds using emulsification and coprecipitation techniques.
Starch Poly(ethyleniminothiourethanes): A Reinforcement Marvel
Starch poly(ethyleniminothiourethanes) emerged as a potent reinforcing agent for rubber compounds. The optimal results were achieved with SX featuring DS values ranging from 0.08 to 0.58 and starch contents spanning 15 to 50 phr. Higher DS and starch content correlated with increased hardness but a decrease in compression set and abrasion resistance.
Unlocking Optimal Formulations: Experimental Design Insights
Buchanan et al. employed experimental design methods to unravel the factors influencing the properties of starch-elastomer compounds. Varied xanthate types, starch loading, xanthate DS, crosslinking, resorcinol-formaldehyde (RF) resin co-reaction, and processing conditions were scrutinized. Notably, high-amylose starch xanthates exhibited inferior physical properties, while flour-based xanthates mirrored starch xanthates but with a deeper color. The sweet spot for optimal rubber compounds was found at 30 phr SX or 45 phr starch xanthide.
Swelling Dynamics and Water Resistance
Starch xanthide-reinforced rubber compounds showcased unique swelling characteristics, surpassing those of conventionally reinforced compounds. Remarkably, this swelling effect proved reversible upon drying. Specific compounds demonstrated the ability to reduce swelling in water, leading to the development of formulations tailored for diverse applications.
Cationic Starch Products: A Solubility Solution
In a bid to fortify carboxylic elastomers, cationic starch products emerged as a game-changer. Resulting compounds exhibited improved physical properties and reduced solubility, achieved through meticulous preparation using solution mixing and drying or a torque rheometer.
In the dynamic realm of rubber reinforcement, the integration of starch compounds brings forth a spectrum of possibilities, from enhancing mechanical properties to mitigating solubility challenges. As research strides forward, these innovations promise to redefine the landscape of rubber applications across various industries.