Polymer Materials for Composites
It is often difficult for a single polymer material to meet the material performance requirements of the production or research, polymer composite materials, therefore, have received extensive attention in both academia and manufacturing industry. Composites not only maintain the main characteristics of raw materials, but often have novel characteristics that raw materials do not have. By preparing composite materials, the following properties can be improved, such as strength, stiffness, toughness, hardness, corrosion resistance, wear resistance, durability, appearance, heat conduction and heat insulation, etc. Since the performance of the composite depends on the type of raw material, shape, proportion and process conditions, it can be easily modulated to obtain composites with different properties.
Characteristics of Polymer in Composites
In order to make the composites superior in performance, the polymer used should have good comprehensive properties. The polymer should be selected reasonably according to the characteristics of the filler and the practical application of the composites to ensure that the inherent properties of the polymer can be maximized.
- Strong adhesion to fillers
An important role of polymer in composites is to act as an adhesive, bonding fillers into a whole, thereby forming a new material with brand-new and improved properties. In addition, the polymer can also play a role in transferring loads in the composite system. For example, fiber fillers cannot withstand bending and compression loads so that they cannot be used as load-bearing materials. However, when they are bonded into a whole by a polymer matrix, their mechanical properties can be improved.
- Good processing performance
When manufacturing composites, it is hoped that there are relatively easy processing and molding conditions to reduce equipment investment, simplify operation and make large-scale products. The polymer used should have a suitable viscosity and shrinkage force, especially the thermoset resin should have a suitable curing time.
Commonly Used Polymer Matrix
There are two main types of polymer matrix: thermoplastic and thermoset. So far, ~95% of polymer composites are thermoset, including unsaturated polyester resin, epoxy resin, phenolic resin, vinyl ester resin, polyimide resin, bismaleimide, polyurethane resin, cyanate resin, silicone resin, etc. Among them, unsaturated polyester, epoxy and phenolic resin are the three most widely used thermosetting resins.
Unsaturated Polyester Resin
Unsaturated polyester is mainly obtained by polycondensation reaction of dibasic acid and diol under the action of heat and/or catalyst. In practical applications, the unsaturated double bonds of the polymers and the double bonds of the crosslinking monomer need to undergo a crosslinking reaction to form a three-dimensional network structure. Unsaturated polyester resin is easy to process, not only can be cured under normal temperature and pressure, but also can be reacted under heating and pressure; at the same time, it is relatively cheap, so it is the most widely used polymer matrix.
The cross-linking reaction of unsaturated polyester is a free radical copolymerization of vinyl monomer (mostly is styrene) and the double bond of unsaturated polyesters. Therefore, the choice of suitable polymerization initiator, polymerization inhibitor and crosslinking agents is very important for the control of resin properties.
Phenolic Resin
Phenolic resin is a polymer formed by polycondensation of phenolic compounds and aldehyde compounds. Among them, the phenolic resin obtained by polycondensation of phenol and formaldehyde is the most important.
Because the phenolic hydroxyl group has strong polarity, it is easy to absorb water to deteriorate the electrical properties and mechanical properties of the material; and the phenolic hydroxyl group is easy to change under the action of heat or ultraviolet light, generating chromophores such as quinone and changing the color of the material. Therefore, it is often necessary to add some substance to modify:
- Polyvinyl acetal --- increasing the toughness of phenolic resin
- Epoxy polymer --- creating resin of excellent adhesion and heat resistance at the same time
- Silicone --- improving the heat resistance and water resistance of phenolic resin
Epoxy Resin
Epoxy resin is a kind of polymer with aliphatic, alicyclic or aromatic segments as the main chain and containing two or more epoxy groups. Epoxy resin has strong adhesion, high chemical stability, corrosion resistance, high strength and modulus, and good electrical properties. It is an ideal insulating material with arc resistance and high dielectric strength.
Uncured epoxy polymers are usually thermoplastic and have little practicality. Only by adding some curing agents appropriately, the three-dimensional network structure is formed through the ring-opening reaction of epoxy groups or hydroxyl groups, which can make the whole material insoluble and infusible.
BOC Sciences supplies the necessary raw materials to help you manufacture ideal composites. Our experienced technicians are available to review and discuss your manufacturing requirements to help you select the right material and will ensure the success of your final products. From additives, modifiers to monomers and polymers, we can cover your compounding requirements.
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