1. Aging type of polymer materials
Polymer materials in the process of processing, storage and use, due to the comprehensive action of internal and external factors, its properties gradually deteriorate, so that the final loss of use value, this phenomenon belongs to the aging of polymer materials.
This not only causes a waste of resources, but even leads to greater accidents due to its functional failure, and the decomposition of materials caused by its aging may also pollute the environment.
Due to different polymer varieties and different conditions of use, there are different aging phenomena and characteristics. In general, the aging of polymer materials can be classified into the following four types of changes:
Changes in appearance
There are stains, blotches, silver lines, cracks, frosting, powdering, hairiness, warping, fisheye, wrinkling, shrinkage, burning, optical distortion and changes in optical color.
Changes in physical properties
Including solubility, swelling, rheological properties and cold resistance, heat resistance, water permeability, air permeability and other properties of change.
Changes in mechanical properties
Tensile strength, bending strength, shear strength, impact strength, relative elongation, stress relaxation, etc.
Changes in electrical properties
Such as surface resistance, volume resistance, dielectric constant, electrical breakdown strength changes.
2. Factors causing aging of polymer materials
Because in polymer processing, the use process, will be affected by heat, oxygen, water, light, microorganism and environmental factors such as chemical medium combination of its chemical composition and structure can produce a series of changes, a corresponding bad physical properties, such as hair hard, brittle, sticky, discoloration, loss of strength and so on, these changes and the phenomenon is called aging.
High polymer under the action of heat or light will form excited molecules, when the energy is high enough, the molecular chain will break to form free radicals, free radicals can form a chain reaction inside the polymer, continue to cause degradation, may also cause cross-linking.
If oxygen or ozone is present in the environment, a series of oxidation reactions can be induced to form hydroperoxides (ROOH), which can be further decomposed into carbonyl groups.
If there are residual catalyst metal ions in the polymer, or metal ions such as copper, iron, manganese and cobalt are introduced into the polymer during processing and use, the oxidation degradation reaction of the polymer will be accelerated.
3. Methods of anti-aging of polymer materials
At present, the main methods to improve and enhance the anti-aging properties of polymer materials are as follows:
The aging of polymer materials, especially the photooxygen aging, first starts from the surface of the material or product, manifested as discoloration, powder, cracking, gloss decline, and then gradually to the interior.
Thin products are more likely to fail earlier than thick products, so the service life of products can be extended by thickening products.
For easy to aging products, can be coated on the surface or coated with a layer of good weather resistance coating, or in the outer layer of the product composite layer of good weather resistance material, so that the surface of the product attached to a layer of protective layer, so as to delay the aging process.
In the process of synthesis or preparation, many materials also have the problem of aging. For example, the effect of heat in the polymerization process, thermal oxygen aging in the processing process and so on. Accordingly, the effect of oxygen can be mitigated by adding deoxygenation devices or vacuuming devices in the polymerization or processing process.
However, this method can only guarantee the performance of the material in the factory, and this method can only be implemented from the source of the material preparation, unable to solve its aging problem in the process of reprocessing and use.
There are groups that are very easy to age in the molecular structure of many polymer materials, so through the molecular structure design of materials, replacing groups that are not easy to age with groups that are easy to age can often play a good effect.
Or the introduction of functional groups or structures with anti-aging effect on the polymer molecular chain by grafting or copolymerization method, endowing the material itself with excellent anti-aging function, is also a method often used by researchers, but the cost is high, and it can not achieve large-scale production and application.
At present, the effective way and common method to improve the aging resistance of polymer materials is to add anti-aging additives, which is widely used because of its low cost and no need to change the existing production process. There are two main ways to add these anti-aging additives:
Direct addition of additives: anti-aging additives (powder or liquid) and resin and other raw materials are directly mixed and stirred after extrusion granulation or injection molding, etc. Because of its simplicity, this way of adding is widely used in many pumping and injection molding factories.
Anti-aging masterbatch addition method: In manufacturers with higher requirements for product quality and quality stability, it is more common to add anti-aging masterbatch in production.
Anti-aging masterbatch is suitable resin as the carrier, mixed with a variety of effective anti-aging additives, then through twin-screw extruder co-extrusion granulation, its application advantages lies in anti-aging additives in the process of preparing masterbatch first implements the dispersed, so late in the process of material processing, anti-aging agent get secondary dispersion, To achieve the purpose of uniform dispersion of auxiliaries in the polymer material matrix, not only to ensure the quality of the product stability, but also to avoid dust pollution during production, making the production more green and environmental protection.
Post time: Aug-17-2022