Basic characteristics and functions of precipitated silica
Precipitated silica (silicon dioxide) is a general term for white, powdery, X-ray amorphous silicic acid and silicate products, mainly including precipitated silica, fumed silica, and ultrafine silica gel. Its chemical composition can be expressed as SiO₂·nH₂O, where nH₂O exists in the form of surface hydroxyl groups. Silica fume possesses the following key characteristics:

Physical properties: Appearance is a white powder or granular form, true density is approximately 2.0 g/mL, apparent density is approximately 0.2 g/mL, it is high-temperature resistant, non-combustible, and has good electrical insulation properties.
Chemical properties: Soluble in caustic alkalis and hydrofluoric acid, insoluble in water, solvents, and acids (except hydrofluoric acid).
Main indicators: SiO₂ content (dry basis) ≥90%, loss on ignition 4.0-8.0%, pH value 5.0-8.0, specific surface area varies between 145-300 m²/g depending on the application.
In adhesives, silica fume mainly performs the following functions:

Thixotropy: Provides shear-thinning properties, improving application performance.
Reinforcement: Enhances the mechanical properties of the adhesive.
Thickening effect: Adjusts the viscosity of the system.
Anti-settling: Prevents filler sedimentation and stratification.
Formulation characteristics of environmentally friendly solvent-based adhesives:
Environmentally friendly solvent-based adhesives are characterized by the absence of volatile organic compounds (VOCs) and harmful substances such as formaldehyde. Their formulation design follows the following principles:

Solvent selection: Using low-toxicity or non-toxic solvents, such as water-based systems or bio-based solvents.
Simplified formulation: Low usage (only 15-35 kg of material per ton of mortar), resulting in a significant environmental benefit.
Rapid dissolution characteristics: The process from powder to adhesive takes only 10 minutes, facilitating on-site preparation and use.
Performance balance: Maintaining necessary bonding strength, weather resistance, and application performance while remaining environmentally friendly.
A typical environmentally friendly adhesive formulation may include:

Polyvinyl alcohol (4%)
Adhesive reactant (0.04%)
Thickener (0.02%)
Film-forming enhancer (0.3%-1.5%)

Through the rational application of silica fume functional filler, environmentally friendly solvent-based adhesives can achieve excellent application and mechanical properties while maintaining environmental friendliness, meeting the needs of modern industry for high-performance adhesives.