Silica plays a crucial role as a functional additive in the modification of novel biodegradable materials (such as PLA), significantly improving the mechanical properties, thermal stability, and functionality of the materials. This provides important technical support for the performance optimization and application expansion of biodegradable materials.
I. Basic Characteristics and Types of Silica
1. Basic Characteristics
Chemical composition: Silica is a general term for white powdery X-ray amorphous silicic acid and silicate products, with the chemical formula SiO₂·nH₂O, where nH₂O exists in the form of surface hydroxyl groups.
Physical characteristics: Porous substance, true density approximately 2.0 g/mL, apparent density approximately 0.2 g/mL, high temperature resistance, non-flammable, odorless, and excellent electrical insulation.
Solubility characteristics: Soluble in caustic alkalis and hydrofluoric acid, insoluble in water, solvents, and acids (except hydrofluoric acid).
2. Main Types
Fumed silica: Under normal conditions, it is a white amorphous flocculent translucent solid colloidal nanoparticle (particle size less than 100 nm), with a purity of up to 99%, a large specific surface area, and a high price.
Precipitated silica: Divided into traditional precipitation method (using sulfuric acid, hydrochloric acid, CO₂, and water glass as raw materials) and special precipitation method (using ultra-gravity technology, sol-gel method, etc.).
Special grades: Such as HT150, ZJ355, etc., with specific particle sizes and specific surface areas, suitable for different application scenarios.

II. Mechanism of Silica in PLA Modification
1. Interfacial Interaction
The silanol groups (-OH) on the surface of silica form hydrogen bonds with the carbonyl groups (C=O) in the PLA molecular chains, enhancing interfacial bonding.
The high specific surface area of silica (usually 145-300 m²/g) provides a large number of interfaces for interaction with PLA, promoting stress transfer.
2. Physical Reinforcement Mechanism
Nanoscale particles (10-100 nm) form physical cross-linking points in the PLA matrix, restricting molecular chain movement and improving material rigidity. Silica nanoparticles act as a nucleating agent, promoting PLA crystallization and improving the material's thermal stability and mechanical properties.

III. Performance Improvement of Silica-Modified PLA
1. Improved Mechanical Properties
Tensile Strength: Adding an appropriate amount of silica can increase the tensile strength of PLA by 20-40%, with the specific increase depending on the type and amount of silica added.
Flexural Strength and Modulus: The flexural strength and modulus of silica-modified PLA are significantly improved, making it particularly suitable for applications requiring high rigidity.
Improved Toughness: Surface-modified silica can effectively improve the brittleness of PLA and increase the impact strength of the material.
2. Optimized Thermal Properties
Heat Distortion Temperature: The addition of silica can increase the heat distortion temperature of PLA by 10-20℃, expanding its application range in high-temperature environments.
Thermal Stability: As a heat stabilizer, silica can delay the degradation process of PLA at high temperatures, extending the material's service life.
3. Functional Expansion
Conductive Properties: Specifically modified silica (such as ZJ355) can impart certain conductivity to PLA, expanding its applications in the electronics field.
Weather Resistance and Anti-aging Properties: Silica can effectively absorb ultraviolet rays, significantly improving the weather resistance and anti-aging properties of PLA and extending its outdoor service life.
Biodegradation Control: Silica can regulate the degradation rate of PLA, achieving controllable degradation to meet the needs of different application scenarios.

IV. Application Fields of Silica-Modified PLA
1. Packaging Materials
Food Packaging: Silica-modified PLA has excellent gas barrier properties and preservation performance, effectively extending the shelf life of food.
Environmentally Friendly Packaging: As a biodegradable material, silica-modified PLA packaging bags can reduce white pollution and conform to the concept of sustainable development.
2. Agricultural Applications
Agricultural Films: Silica-modified PLA films have good light transmittance and heat retention properties, and can also incorporate pesticides for controlled release, increasing crop yields.
Soil Improvement: Silica can improve soil structure, enhance water and fertilizer retention capacity, and promote the growth of crops such as rice. 3. Medical and Daily Necessities
Medical materials: Silica-modified PLA can be used to prepare biodegradable medical stents, sutures, etc., possessing good biocompatibility and controllable degradability.
Daily necessities: Such as biodegradable tableware and disposable products, meeting environmental protection requirements while maintaining good performance.

V. Latest Advances in Silica Modification Technology
1. Surface Modification Methods
Coupling agent modification: Treating the silica surface with silane coupling agents to improve its compatibility with PLA is currently the most widely used modification method.
Ionic liquid modification: Using ionic liquid modifiers instead of traditional organic phase modifiers, offering advantages such as being liquid at room temperature, high conductivity, and high stability.
Macromolecular interface modification: Using macromolecular polymers containing polar groups as modifiers to improve the interfacial bonding force between silica and PLA.
2. Innovative Applications
PP silica modification: Compounding silica with polypropylene to improve the material's stiffness, hardness, and strength, while also improving impact resistance and weather resistance.
HT150 silica: Its application in PLA can significantly improve the material's conductivity and chemical stability, suitable for electronics, plastics, coatings, and other fields.
ZJ355 silica: Possessing high purity (over 97%) and a nano-scale particle structure, it can be used as a high-efficiency whitening agent and high-performance filler, widely used in plastics, rubber, coatings, and other fields.

VI. Future Development Trends
1. Technological Innovation Directions
Structural control: In-depth research into the relationship between the microstructure of silica and the performance of PLA to achieve targeted design and optimization of material properties.
Multifunctional modification: Through a combination of various modification methods, enabling silica-modified PLA to possess multiple functions such as conductivity and fluorescence, expanding its application fields.
Nano-scale modification: Utilizing nanotechnology to prepare highly dispersed, well-compatible silica nanocomposite materials to improve the overall performance of the material.
2. Application Expansion Prospects
Environmental protection field: The application of silica-modified PLA in environmentally friendly packaging, agricultural films, and other fields will become more widespread, contributing to sustainable development. Electronics field: With improved conductivity, carbon black-modified PLA is expected to achieve breakthrough applications in flexible electronic devices, sensors, and other fields.
Medical field: By controlling the degradation rate and biocompatibility, carbon black-modified PLA will play a greater role in tissue engineering, drug sustained release, and other medical fields.
The application of carbon black as a functional additive in PLA modification not only solves key problems such as insufficient mechanical properties and poor thermal stability of PLA, but also endows the material with more functionality, providing important technical support for the performance optimization and application expansion of biodegradable materials. With the continuous advancement of modification technology, carbon black-modified PLA will demonstrate its unique value in more fields, making a greater contribution to sustainable development and environmental protection.