Mechanism of Swelling
Water swelling rubber functions by absorbing water when it comes into contact with it. Water molecules infiltrate the rubber through processes like diffusion, capillary action, and surface adsorption. Once the forces resisting deformation and the osmotic pressure reach equilibrium, the water-absorbing rubber maintains a stable effect for water-stopping and leak-plugging.
Main Components
Water swelling rubber consists of a rubber matrix and hydrophilic components. The rubber matrix’s elasticity and strength dictate the rubber’s physical properties. Typically, rubbers with high elasticity and excellent adhesion, such as chloroprene rubber (CR), styrene-butadiene rubber (SBR), and chlorinated polyethylene (CPE), are used.
The hydrophilic materials are crucial for creating water swelling rubber. These components include natural polymers, hydrophilic polymers, superabsorbent resins, and various water-absorbent inorganic substances. Superabsorbent resins are particularly favored due to their high water absorption, swelling rates, and strong water retention capabilities.
Types of Superabsorbent Resins
- Starch-based Resins: Starch molecules have numerous hydroxyl groups, allowing for the creation of various starch derivatives through hydroxyl group reactions.
- Cellulose-based Resins: Made from β-d-glucose, these resins can undergo grafted copolymerization with low-molecular hydrophilic unsaturated substances.
- Synthetic Resins: These include copolymers like vinyl acetate and methyl acrylate, polyacrylamides, PAANa cross-linked products, and polyvinyl alcohol-acrylic acid graft copolymers. Ionic superabsorbent resins are often used due to their rapid water absorption.
- Biodegradable Resins: Environmentally friendly options like polylactic acid, sodium alginate, polyamino acids, and chitosan offer high water absorption and are degradable.
- Organic-Inorganic Composite Resins: Recently, composite materials such as kaolin, bentonite/montmorillonite, talc, attapulgite, and diatomite have been integrated into superabsorbent resins.
Application Prospects
Water swelling rubber can absorb many times its own weight in water while maintaining elasticity and strength, making it valuable in various applications. It is widely used in waterproof sealing materials, medical and sanitary products, toys, and anti-condensation wall materials. It effectively addresses sealing issues caused by the permanent deformation of rubber and cement, as well as shrinkage-related waterproofing and leak-proofing challenges.
Due to its excellent adhesion with both polar surfaces (asphalt, plastic, rubber) and non-polar surfaces (cement mortar, reinforced cement), water swelling rubber is ideal for tunnels, subways, culverts, construction, and underground engineering projects. It is also used in offshore oil production facilities and serves as a superior waterproof and moisture-proof sealing material for automobiles, containers, precision instruments, medicines, and food.
Additionally, water-absorbing rubber functions as a soil conditioner and water-retaining agent, especially beneficial in arid regions and during dry seasons. Its high sensitivity to temperature, pH, and salt concentration makes it suitable for water-sensitive sensors in medical and physiological applications.