What exactly are chemical rubber additives? How are they different from physical additives?
As an important elastic material, rubber is widely used in many fields such as automobiles, construction, electronics, and medical treatment. In order to improve the performance, processability, and quality of rubber products, a variety of additives need to be added during the production process. Rubber additives are divided into two categories: chemical additives and physical additives, among which chemical rubber additives are one of the cores of rubber formula design.
This article will introduce in detail the definition, function, main types, and differences between chemical rubber additives and physical additives to help readers deeply understand the characteristics and application scenarios of these two types of additives.
1. What are chemical rubber additives?
1. Definition
Chemical rubber additives refer to a class of additives that change the molecular structure of rubber or promote the improvement of rubber physical properties through chemical reactions during rubber mixing and vulcanization. They participate in or catalyze the crosslinking, modification, and curing of rubber, and improve the mechanical properties, heat resistance, chemical resistance, and service life of rubber products.
In other words, chemical additives not only exist as functional components in the formula, but also react chemically with rubber molecules to form new chemical bonds and improve rubber performance.
2. Mechanism of Action
Chemical rubber additives mainly work in the following ways:
Promoting vulcanization and cross-linking reactions: such as vulcanizers and accelerators, by promoting cross-linking between rubber molecules to form a three-dimensional network structure, improve elasticity and strength.
Chemically modifying rubber molecules: such as antioxidants and anti-ozonants, forming a protective layer on the rubber molecular chain to prevent environmental oxidation and degradation.
Assisting in rubber structure adjustment: such as active fillers and cross-linking agents, enhancing the compatibility of rubber and fillers through chemical bonding and improving mechanical properties.
II. Main types and functions of chemical rubber additives
1. Vulcanizing Agents
Vulcanizing agents are the most critical category of chemical additives. Rubber promotes cross-linking between molecular chains through vulcanizing agents to form an elastic network. Commonly used vulcanizing agents include:
Sulfur: a traditional and widely used vulcanizing agent, suitable for natural rubber and most synthetic rubbers.
Peroxides: used for cross-linking of special synthetic rubbers to provide heat resistance and aging resistance.
Metal oxides: such as zinc oxide, used as auxiliary vulcanizing agents in some rubber systems.
2. Accelerators
Accelerate the vulcanization reaction rate, shorten the vulcanization time, improve production efficiency, and improve the physical properties of vulcanized rubber. Common vulcanization accelerators are:
Thiazoles (such as CBS, MBTS)
Mercaptans
Dithiocarbamates
3. Antioxidants
Prevent rubber chains from breaking due to oxygen during processing and use, and extend the life of rubber. Common antioxidants are:
Amine antioxidants: highly efficient but dark in color, suitable for products with low color requirements.
Phenolic antioxidants: light in color, good in durability, often used in high-end products such as tires.
4. Antiozonants
Prevent ozone from causing cracking on the rubber surface, especially suitable for outdoor rubber products. Commonly used are:
Phosphine compounds
Carbamates
5. Cross-linking accelerators and synergists
Improve cross-linking efficiency and improve the mechanical properties of vulcanized rubber, such as coupling agents (silane coupling agents, etc.) that promote the bonding of rubber and fillers.
3. Concept and characteristics of physical rubber additives
1. Definition
Physical rubber additives mainly refer to additives that do not undergo chemical reactions during the rubber mixing process and improve the processability, rheological properties, appearance or filling effect of rubber by physical means.
2. Main types
Fillers: such as carbon black, white carbon black, and clay, used to enhance rubber strength and wear resistance.
Plasticizers (softeners): improve the softness and processing fluidity of rubber.
Processing aids: such as anti-sticking agents and release agents, which facilitate rubber molding processing.
3. Mechanism of action
Physical additives mainly improve the performance of rubber formulas through physical interactions with rubber molecular chains, such as adsorption, dispersion, lubrication, etc., but do not participate in the formation of chemical bonds.
4. The difference between chemical rubber additives and physical additives
Aspects Chemical rubber additives Physical rubber additives
Action mode Participate in the chemical reaction of rubber molecules to form new chemical bonds Improve rubber properties through physical action, no chemical reaction occurs
Main functions Promote vulcanization, cross-linking, anti-oxidation, enhance structural stability Improve processing performance, improve filling effect, and enhance flexibility
Typical varieties Vulcanizers, accelerators, antioxidants, cross-linking agents Fillers (carbon black, silicone), plasticizers, anti-sticking agents
Influence on performance Improve rubber mechanical properties, aging resistance, and heat resistance Improve rubber processing fluidity and appearance
Chemical reaction participation Must participate in chemical reactions Do not participate in chemical reactions
V. Specific differences and coordination in applications
In the production of rubber products, chemical additives and physical additives are often used in combination to work synergistically. Take tire production as an example:
Physical additives such as carbon black enhance the wear resistance and strength of rubber, and plasticizers improve the softness and processability of rubber;
Chemical additives such as vulcanizers and accelerators ensure that tires have excellent elasticity and heat resistance, and antioxidants extend tire life.
Both are indispensable and jointly determine the comprehensive performance of rubber products.
VI. Summary
Chemical rubber additives are an indispensable and important part of rubber product manufacturing, mainly improving product performance by promoting cross-linking of rubber molecules and preventing degradation. Unlike physical rubber additives, chemical additives change the molecular structure of rubber by participating in chemical reactions, while physical additives mainly rely on physical methods to improve the processing and physical properties of rubber.
In the future, as the performance requirements of rubber products continue to increase, the functions and technologies of chemical additives will continue to innovate, and green environmental protection, functionalization and diversification will become the development trend. At the same time, the combination of physical additives and chemical additives will be more refined and scientific, providing strong guarantees for high-performance rubber products.
