PP material is a kind of polypropylene material, which is widely used at present. By modifying the PP material, a more effective material can be obtained.
However, many people don't know what the PP material is, and want to know what chemical modification is. Today, the editor will introduce in detail "What are PP materials and what are the chemical modifications?"
1. What is PP material?
Polypropylene, a kind of plastic, is a linear polymer with high density, no side chains, and high crystallinity, with excellent comprehensive properties. Common products: basins, barrels, furniture, films, woven bags, bottle caps, car bumpers, etc.
pp plastic, chemical name: polypropylene English name: Polypropylene (abbreviated as pp) Proportion: 0, 9-0, 91 g/cm3 Molding shrinkage rate: 1, 0-2, 5% Molding temperature: 160-220℃ PP is Crystalline polymer, PP has better overall performance than PE material. PP products have light weight, good toughness and good chemical resistance.
Disadvantages of PP: low dimensional accuracy, insufficient rigidity, poor weather resistance, it has post-shrinkage phenomenon, after demolding, it is easy to age, become brittle, and easy to deform. In daily life, the commonly used fresh-keeping box is made of PP material.
2. Chemical modification of PP material
1. Copolymerization modification
Copolymerization modification is a modification carried out at the stage of propylene monomer synthesis using catalysts such as metallocene. When the monomers are polymerized, the added olefin monomers are copolymerized with them to obtain random copolymers, block copolymers and alternating copolymers. The mechanical properties, transparency and processing fluidity of homopolymer PP are all improved. .
The complex formed by the metallocene catalyst uses a transition state with irregular shapes as a single active center to achieve precise control of the relative molecular mass and its distribution, comonomer content, distribution on the main chain, and polymer crystal form. structure.
2. Graft modification
PP (polypropylene) resin molecules have a non-polar crystalline linear structure with low surface activity and no polarity. There are disadvantages such as poor surface printability; poor coating adhesion; difficult to blend with polar polymers; and difficult to be compatible with polar reinforcing fibers and fillers.
Graft modification is to introduce polar groups into the macromolecular chain to improve the blending, compatibility and cohesiveness of PP, so as to overcome the shortcomings of difficult blending, difficult compatibility and difficult bonding. Under the action of the initiator, the grafting monomer undergoes grafting reaction during melting and mixing. The initiator decomposes to produce active free radicals when heated, melted and heated. When the active free radicals encounter unsaturated carboxylic acid monomers, it promotes unsaturated carboxylic acid. After the unstable bond of the acid monomer is opened, it reacts with the active free radical of PP to form the grafting free radical, which is then terminated by a molecular chain transfer reaction.
The common graft modification methods of PP include: melting method, solution method, solid phase method, suspension method and so on. The hydrogen atoms in the PP molecular chain after graft modification are replaced to show strong polarity. These polar groups enhance the compatibility of PP, and the heat resistance and mechanical properties are greatly improved.
3. Cross-linking modification
Cross-linking modification is mainly to modify linear or dendritic polymers into network-like polymers through cross-linking methods. PP (polypropylene) cross-linking modification can improve its mechanical properties, heat resistance and morphological stability, and shorten the molding cycle.
The main methods of cross-linking modification of polypropylene are chemical cross-linking modification and radiation cross-linking modification. The main difference is that the cross-linking mechanism is different and the active source is different; the chemical cross-linking modification is realized by adding a cross-linking auxiliary agent. Modification, radiation cross-linking modification is mainly achieved through strong radiation or strong light. Due to the requirement of radiation cross-linking modification for the thickness of PP, it is difficult to popularize this method.
At present, the silane grafting and crosslinking method is developing rapidly due to its ability to prepare materials with excellent properties. The PP produced by the silane grafting and crosslinking method has high strength, good heat resistance, high melt strength, strong chemical stability, and corrosion resistance. good.
