1 Introduction
1.1 Wide application of rubber products
Rubber goods’ exceptional physical qualities, including elasticity, wear resistance, and chemical resistance, have made them become materials that are essential to contemporary industry. They are important players in a wide range of industries, including sports, electronics, medical devices, automobile production, aircraft, and ordinary consumer goods. Rubber goods give customers a more pleasant experience in addition to extending the product’s life and functionality.
1.2 Effect of aging on the performance of rubber products
Over time, rubber goods may unavoidably experience aging issues. Rubber materials age as a result of exposure to many environmental conditions, including temperature, humidity, light, oxygen, and mechanical stress. As a result, the materials eventually lose their initial physical and chemical characteristics. The rubber will grow hard, brittle, and may fracture and shatter as a result of this process, which would negatively impact the product’s dependability and safety.
1.3 The importance of appearance changes after aging
Aging-related changes in appearance are a logical indicator of a deterioration in rubber product performance. Evident indicators of aging include color fading, surface crack development, gloss loss, etc. These alterations not only impact the product’s aesthetic appeal but also point to possible hazards to its functionality. Thus, keeping an eye on and assessing how look changes with ageing products is essential to averting product malfunctions, prolonging product life, and upholding brand reputation.
2. Basic concepts of aging of rubber products
2.1 Definition of aging
Aging is the process by which rubber materials’ physical characteristics, chemical makeup, and aesthetic qualities gradually deteriorate as a result of several internal and external factors at play throughout the materials’ manufacture, processing, and usage. In the life cycle of rubber goods, aging is a natural occurrence that is closely linked to the product’s performance and service life.
2.2 Types of aging: physical aging and chemical aging
Aging can be roughly divided into two types: physical aging and chemical aging.
Physical aging: Generally speaking, this term describes how temperature variations, mechanical stress, and other variables alter the orientation and arrangement of molecular chains during the usage of rubber materials, causing a decline in performance. Aging physically might show itself as harder skin, less suppleness, etc.
Chemical aging is the term used to describe how rubber materials respond chemically to the environment around them. These processes might include oxidation, thermal degradation, photodegradation, and others that break down or cross-link molecules in the rubber’s molecular chains and deteriorate the material’s qualities. Rubber may harden, break, or experience other chemical changes as a result of chemical aging.
2.3 Factors affecting the aging process: environment, temperature, light, mechanical stress, etc.
The aging process is affected by many factors, including:
Environmental factors: Rubber aging is affected by oxygen, moisture, chemicals, and other elements in the air in the area where rubber goods are stored.
Temperature: One of the main elements influencing rubber aging is temperature. Rubber will age more quickly at high temperatures because of its accelerated chemical reaction; in low temperatures, rubber may become brittle and rigid.
Light: Rubber will get discolored, stiffen, and lose its performance as a result of photodegradation, which is the breakdown of rubber’s chemical bonds under prolonged UV exposure.
Mechanical stress: When rubber goods are used, mechanical stress such as strain, compression, and distortion occurs. This stress will hasten both the physical and chemical aging processes.
3. Chemical mechanism of rubber aging
3.1 Oxidation reaction
One of the most frequent chemical reactions in rubber aging is the oxidation reaction. Rubber molecules containing double bonds or reactive groups combine with oxygen molecules in the presence of oxygen to create peroxide. These peroxides break down even further to produce free radicals, which set off a series of events that eventually break or cross-link rubber molecules, losing some of their original qualities.
3.2 Thermal degradation
The chemical breakdown of rubber at high temperatures is referred to as thermal deterioration. Rubber goods may break apart into tiny molecular fragments when subjected to high temperatures, which may lessen the material’s physical characteristics. Rubber can also become brittle and harden due to thermal breakdown.
3.3 Photodegradation
Rubber undergoes a chemical process known as photodegradation when it is exposed to UV light or other light sources. Rubber molecules’ chemical bonds may be broken by ultraviolet radiation, which also causes the molecular chains to split and produce new chemical groups like double bonds. The rubber may become less elastic, lose strength, and change color as a result of these modifications.
3.4 Ozone destruction
One particular kind of rubber aging that mostly affects unsaturated rubber is ozone degradation. When ozone molecules interact with the double bonds in rubber, they create fissures that have the potential to pierce the rubber’s whole composition and result in material failure. Ozone damage often affects rubber materials in locations where stress is concentrated, such bending or tensile parts.
3.5 Microbial erosion
The biodegradation of rubber compounds by microorganisms like fungus and bacteria is referred to as microbial assault. Rubber’s organic components may be broken down by microbes at the right temperature and humidity levels, which would reduce the material’s performance. Rubber typically experiences microbial assault in settings where it comes into touch with dirt, water, or organic materials.
4. Effect of aging on rubber appearance
4.1 Color changes: yellowing, fading
Rubber’s color may alter as it ages; yellowing and fading are frequent color changes. Oxidation processes are often the source of yellowing, particularly in rubber that contains phenolic antioxidants. Photodegradation could be the cause of fading. The rubber’s pigments and dyes are destroyed by UV light, which causes the color to progressively fade.
4.2 Surface cracks: micro cracks, macro cracks
Rubber ages and develops many kinds of surface fissures. Small surface fractures known as microcracks are frequently brought on by internal forces and microstructure alterations. Macroscopic cracks are more visible and can result from environmental or external stressors including temperature fluctuations, mechanical stress, or chemical damage.
4.3 Surface roughness changes
The rubber surface’s roughness varies as well with age. This might be the result of surface fractures forming and growing, or it could be the result of the rubber material’s surface layer becoming uneven as a result of chemical or physical impacts.
4.4 Expansion and contraction
As rubber ages, it may experience expansion and shrinkage in volume. While shrinking might be the consequence of broken molecules or the material losing its flexibility, swelling is often caused by chemical processes inside the rubber that raise the cross-link density.
4.5 Hardening and Softening
Rubber’s hardness varies as a result of aging. Rubber undergoes hardening, which is characterized by a hardening and brittleness that may be brought on by increased molecule cross-linking or increased intermolecular pressures. Conversely, softening refers to the process of the rubber becoming softer, maybe as a result of a decrease in cross-link density or the breakdown of molecular chains.
5. Analysis of appearance characteristics of rubber aging
5.1 Relationship between aging degree and appearance changes
The degree of age and variations in rubber’s look are closely related. Rubber will age and alter in appearance over time; these variations may be used as key markers to assess how far along rubber is in the aging process. Severe aging, on the other hand, may cause obvious cracking, hardness, or softening, whereas moderate aging could just cause a little change in color or loss of surface sheen.
5.2 Observation methods of aging characteristics: visual inspection, tactile inspection
Observation of aging characteristics can be carried out through the following methods:
Visual inspection: Use a magnifying glass or your unaided eye to look for color changes, shine, cracks, and other obvious flaws on the rubber surface. Making an initial evaluation quickly and easily may be done through visual inspection.
Tactile inspection: You may sense variations in the rubber’s hardness, elasticity, and surface roughness by touching its surface. Visual information about changes in the physical characteristics of rubber can be obtained through tactile investigation.
5.3 Quantitative analysis of aging characteristics: hardness test, tensile strength test
In order to more accurately evaluate the aging characteristics of rubber, the following quantitative analysis methods can be used:
Hardness test: Using a durometer to measure rubber’s hardness, one may determine how much the material has aged and gotten softer or harder. One significant physical attribute indication that changes with ageing is hardness.
Tensile strength test: To determine the stress and strain that will cause the rubber sample to break, it is stretched using a tensile testing apparatus. If rubber ages, it may lose some of its toughness and elasticity. This can be shown by changes in tensile strength and elongation.
6. Aging appearance changes of different types of rubber products
6.1 Natural rubber
Natural rubber (NR) is a common all-purpose rubber that is primarily made from the latex of rubber trees. The following alterations in appearance are possible with aged natural rubber:
Color Change: Oxidation can cause natural rubber to progressively turn yellow.
Crack formation: After prolonged exposure to air, particularly to high temperatures or UV radiation, natural rubber may start to show microcracks on its surface.
Hardening: Natural rubber may become less elastic and harder with time.
6.2 Styrene-butadiene rubber
Synthetic rubber known as styrene-butadiene rubber, or SBR, is frequently used in the production of tires and other industrial goods. Aging may have the following impacts on styrene-butadiene rubber:
Rough surface: Photodegradation and heat deterioration can cause the surface of styrene-butadiene rubber to become rough.
Color Degradation: When exposed to UV radiation for a lengthy amount of time, SBR may fade or change color.
Performance degradation: Styrene-butadiene rubber’s toughness and tensile strength may deteriorate with age.
6.3 Silicone rubber
Silicone rubber (SiR) is widely utilized in medical gadgets and kitchen utensils due to its exceptional temperature and weather resistance. When silicone rubber ages, it can undergo cosmetic changes such as:
Loss of gloss: The silicone rubber’s surface may become less shiny after extended use.
Surface cracks: Despite silicone rubber’s strong aging resistance, severe circumstances can nevertheless cause cracks to form.
Hardening or Softening: Silicone rubber’s hardness may alter with age.
6.4 Neoprene
Neoprene (CR), sometimes referred to as chloroprene rubber, is frequently used in hoses and seals because of its strong resistance to chemicals and oils. The following are possible cosmetic impacts of aging on neoprene:
Color Change: Oxidation can cause neoprene to change color, especially darkening or yellowing.
Propagation of cracks: Long-term mechanical stress or environmental variables can cause cracks to develop on the surface of neoprene.
Hardening phenomenon: Neoprene’s flexibility and sealing qualities may be impacted by the hardening process that comes with aging.
7. Prevention and repair of aging appearance of rubber products
7.1 Material selection and formula optimization
The first steps in cosmetic anti-aging prevention are material selection and formulation optimization. The aging resistance of rubber goods may be greatly increased by choosing the right base polymer and additives.
Base polymer: Select a polymer, such silicone rubber or fluoroelastomer, that naturally resists aging.
Antioxidants: To stop oxidation processes and increase rubber’s longevity, antioxidants are added.
Light Stabilizers: To shield rubber from UV deterioration, use light stabilizers and UV absorbers.
Thermal Stabilizers: In hot conditions, use thermal stabilizers to stop thermal deterioration.
7.2 Improvement of processing technology
Delaying rubber aging also requires better processing methods.
Vulcanization conditions: To guarantee that the rubber is completely vulcanized and to increase its resistance to heat and chemicals, optimize the vulcanization temperature and duration.
Combining Differentiation: makes certain that every component is distributed equally throughout the rubber matrix, preventing chemical reactions or localized overheating.
Release of tension: Take action to lessen the development of microcracks by releasing internal stress during processing.
7.3 Surface treatment technology: coating, plating
Rubber goods can benefit from an extra layer of protection and a slowed down aging process thanks to surface treatment technologies.
Coating: To shield the rubber from moisture and UV radiation, apply a weather-resistant coating.
Coating: To increase the rubber’s resistance to wear and aging, coat it with a coating of wear-resistant material, such as polytetrafluoroethylene (PTFE).
7.4 Repair methods after aging: polishing, filling, replacement
If your rubber product has aged, you can use the following repair techniques.
Grinding: Grinding can be used to remove the aging layer and restore the smoothness of surfaces with cracks and variations in roughness.
filler: To stop a fracture from spreading, small cracks and flaws may be fixed using the right filler material.
Replacement: This can be the most economical course of action for rubber items whose performance has significantly declined or who are quite old.
