Application of modified unsaturated polyester in FRP

Unsaturated polyester resin is one of the main varieties of thermosetting resin. Pure unsaturated polyvinyl acetate resin becomes thermosetting material after curing, and its mechanical strength is low, which is difficult to meet the requirements of most application fields. Generally, glass fiber is used to strengthen it to become a composite material. Unsaturated polyvinyl acetate resin is an important variety in the development of modern plastic industry, mainly divided into reinforced and non-reinforced series, which can be widely used in many fields such as industry, agriculture, transportation, transportation, construction and national defense industry.

China's FRP reinforced products mainly include cooling towers, boats, chemical anti-corrosion equipment, vehicle parts, doors and windows, mobile rooms, sanitary equipment, food equipment, entertainment equipment and sports equipment. The main varieties of non-reinforced products include furniture coatings, Polaroid plates, buttons, ivory and jade imitation handicrafts, artificial marble, artificial agate, artificial granite, etc.

Performance weakness of unsaturated polyester:

The volume shrinkage rate is large when curing, the odor and toxicity are large when molding, the heat resistance, strength and modulus are low, the toughness is poor, and the deformation is easy. The resistance to organic solvents is poor. The molecular structure of unsaturated polyester contains unsaturated double bonds and has the characteristics of double bonds. At high temperature, the double bonds will open, cross linked and self-polymerize; Copolymerization with other olefinic monomers through the addition reaction of double bonds; Under certain conditions, the double bond is also easy to be oxidized, resulting in the deterioration of polyester quality. The ester bond in polyester is easy to be hydrolyzed by acid and alkali to destroy its physical and chemical properties, and the polyester itself degrades.

Modification method and performance after modification:

1. Low shrinkage modification. The curing shrinkage of unsaturated polyester resin requires low or even zero shrinkage. The preparation method of this kind of unsaturated polyester resin is mainly to introduce low shrinkage agents into the resin, such as polyethylene, polyvinyl chloride, polystyrene, polymethyl methacrylate or diallyl phthalate. For example, low shrinkage agent with PVAc at one end and PS at the other end synthesized by copolymerization can not only obtain products with good shrinkage, but also obtain good coloring effect.

2. Toughening modification. After curing, UPR is brittle and has poor impact strength. In order to improve the impact resistance of polyester products, it is often necessary to modify the toughness of UPR.

From the point of view of UPR molecular main chain, the more long chain structure introduced, the more flexible the molecule is, and the higher impact strength in mechanical properties. In the synthesis of UPR, the introduction of long-chain alcohol and long-chain acid is the most convenient method. The common binary alcohols include diethylene glycol, triethylene glycol and polyethylene glycol; Dibasic acids include adipic acid, etc. Both long-chain alcohol and long-chain acid can improve the flexibility of UPR and reduce the strength of resin. The flexibility of UPR can also be improved by improving the symmetry of molecular main chain.

The toughness of resin products can also be improved by adding some thermoplastic elastomers to UPR. Commonly used thermoplastic elastomers for blending modification, such as liquid rubber, liquid polyurethane, etc. This modified system presents the characteristics of homogeneous structure, can effectively transfer stress, give full play to the flexibility of rubber itself, and reduce the damage of external force to the resin matrix. For example, the used vulcanizate powder (RP) is used as the active filler to modify the block molding compound (BMC) with UPR as the matrix resin. When RP is filled into the resin, it is found that the impact strength is improved and the curing shrinkage is further reduced.

One polymer can also toughen UPR by cross-linking in another polymer to form interpenetrating network structure (IPN), which is a new way to toughen UPR. If it is a physical method, the effect of strengthening and toughening can be achieved by adding other components, such as rigid particles.

3. Flame retardant modification. There are two ways to improve the flame retardancy of UPR: one is to select the resin with flame retardancy, such as the S320 of Jinling DSM; 907 resin, etc; The other is to add flame retardant to UPR.

4. Medium resistance modification. When used under the condition of strong corrosion or solvent, this will cause the filler of UPR to exude or change its structure, and cause degradation or cross-linking, thus losing its excellent characteristics. This working environment requires UPR with strong medium resistance, which can usually react with stable raw materials to enhance the medium resistance. Modification can also be achieved by end sealing.

5. Other modification methods. Use degradable plant fiber instead of traditional glass fiber to strengthen UPR. It is found that the composite made of 25% bamboo fiber and 75% glass fiber has good mechanical properties, with tensile strength of 37 MPa, bending strength of 140 MPa and impact strength of 32 kJPm2. Using wood flour to improve the properties of UP, it was found that the compressive strength of composite material (wood flour PUP) was significantly higher than that of UP.

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