Thermoplastic resins have the properties of softening when heated and hardening when cooled, and they do not react chemically. No matter how many times the heating and cooling are repeated, they can maintain this property. All thermoplastic resins have a linear molecular structure. It includes all polymerized resins and partially condensed resins.

Structure

Thermoplastic resins are mainly made of petrochemical products and have a large output. They account for about 90% of the total output of synthetic resins in the world. Commonly used thermoplastic resins are: polyethylene, polypropylene, polyvinyl chloride, polystyrene, polymethyl methacrylate, polyester, polyoxymethylene, polyamide, polyphenylene ether, etc. Thermoplastic resins can be divided into two categories according to their aggregated structure: crystalline (such as polyamide) and amorphous (such as polymethyl methacrylate). Due to the refraction of crystal grains, crystalline resins have poor transparency, high melting point, and large molding shrinkage. The light transmittance of some varieties of amorphous resins is comparable to that of inorganic glass, and the processing shrinkage is also small.

Preparation

Thermoplastics can be made by adding various plastic additives, such as antioxidants, plasticizers, etc., as well as various reinforcing materials, to thermoplastic resins. Some varieties (such as polyesters and polyamides) have very little additives, and pure resins can be directly processed; some varieties (such as polyvinyl chloride) have extremely complex formulas, and different formulas have different properties. Common processing methods for thermoplastics include extrusion, blow molding and injection molding.

In the polymerization process of producing thermoplastic resins, those with carbon chains as macromolecular chains are generally prepared by addition polymerization, and those with heterochains as macromolecular chains are prepared by condensation polymerization. Thermoplastic resins are mainly used as thermoplastics, and are also used as adhesives and coatings. Most resins used for synthetic fibers are thermoplastic resins.

In the future, the output of thermoplastic resins will still account for the vast majority of the total output of synthetic resins. The number of varieties with completely new chemical structures will not increase too much, but there will be new improvements in production processes. It is still an important direction to seek thermoplastic resins that are resistant to high temperatures, easy to process, high in strength, or have certain special functions (such as conductivity).

Characteristics

A large class of synthetic resins (also including common natural resins) that can be repeatedly heated to soften and cooled to solidify. This type of resin is a high molecular weight solid at room temperature. It is a linear or slightly branched polymer. There is no cross-linking between molecules. They only attract each other with the help of van der Waals forces or hydrogen bonds. During the molding process, the resin softens and flows by pressurizing and heating, and no chemical cross-linking occurs. It can be shaped in the mold and cooled to form the desired shape. During repeated heating, the molecular structure basically does not change. When the temperature is too high or the time is too long, it will degrade or decompose. These are the characteristics that distinguish it from thermosetting resins.

Mechanical properties

There are five structural factors that determine the mechanical properties of synthetic resins:

¢ÙThe main force of the macromolecular chain;

¢ÚThe force between molecules;

¢ÛThe flexibility of the macromolecular chain;

¢ÜMolecular weight;

¢ÝThe cross-linking density of the macromolecular chain.

The significant difference in structure between thermoplastic resins and thermosetting resins is that the macromolecular chain of the former is a linear structure, while the macromolecular chain of the latter is a body network structure. Due to this structural difference, thermoplastic resins have the following significant characteristics in mechanical properties compared with thermosetting resins:

¢ÙIt has obvious mechanical relaxation phenomenon;

¢ÚUnder the action of external force, the ability to deform is relatively large, that is, when the strain rate is not large, it can have a considerable elongation at break;

¢ÛGood impact resistance.

Electrical properties

The electrical properties of thermoplastic resins can be divided into the following categories according to the polarity of their macromolecules:

(1) Non-polar resins such as polyethylene, polybutadiene, polytetrafluoroethylene, etc.

(2) Weakly polar resins such as polystyrene, polyisobutylene, natural rubber, etc.

(3) Polar resins such as polyvinyl chloride, polyvinyl acetate, polyamide, polymethyl methacrylate, etc.

(4) Strongly polar resins such as polyester.

Non-polar resins have excellent insulation properties, are stable to corrosive media, and can be used as high-frequency electrolytes. Weakly polar and polar resins can be used in medium-frequency electrical technology. Strongly polar resins can only be used as low-frequency dielectrics.

Chemical properties

Solubility

This resin product is soluble in aromatic, fatty, ester and ketone solvents.

Miscibility

This resin product can be melted with C5 petroleum resin, EVA, etc. to produce hot melt marking paint.

Packing specifications:

Granular or flake, composite textile paper bag or plastic woven bag, net weight 25 kg/bag.

Storage: Store in a cool and dry place, not wet with water, not near fire.

Technical indicators:

Project; Indicator

Appearance; light yellow transparent semicircular granules

Color (Ghana color number) (50% toluene solution) not more than 3 acid value not more than 15mgKOH/g

Softening point (ring and ball method) 90-105¡æ

Application range

White or yellow hot melt road marking paint, various paints, inks.

Solubility

This resin product is soluble in aromatic, fatty, ester and ketone solvents.

Miscibility

This resin product can be melted with C5 petroleum resin, EVA, etc. to produce hot melt marking paint.

Packing specifications

Granular or flake, composite textile paper bag or plastic woven bag, net weight 25 kg/bag.

Storage

Store in a cool and dry place, away from water and fire.

Application

The resin product is specially used in the production of hot melt road marking paint, with the characteristics of light color, anti-yellowing and good thermal stability. Within the typical construction temperature range required by road marking paint, the resin has excellent viscosity stability and flow consistency, and its coating has strong adhesion, high hardness, good abrasion resistance and anti-pollution, and does not pollute the construction environment. White or yellow hot melt resin is used in road marking paint, various paints, and inks.

Classification

Thermoplastic resins include: PE-polyethylene, PP-polypropylene, PVC-polyvinyl chloride, PS-polystyrene, PA-polyamide, POM-polyoxymethylene, PC-polycarbonate, polyphenylene ether, polysulfone, rubber, etc. The advantages of thermoplastic resins are simple processing and high mechanical energy. The disadvantages are poor heat resistance and rigidity.

Rosin modified thermoplastic resin is an irregular semicircular granular product made from modified rosin after glycerol esterification.

Development Status

In resin-based composite materials, the resin plays the role of fixing the fiber and sharing the stress transmitted by the fiber. The thermal properties, corrosion resistance and processing properties of the material are all reflected by it. Among the advanced resin-based composite materials used in aerospace products, the resin matrix is mainly thermoplastic resin: polyamide (PA), polyetheretherketone (PEEK), PPS, polyimide (PI), polyetherimide (PAI), etc.

PA

PA, commonly known as nylon, is a general term for resins containing repeated amide groups on the molecular chain. It is prepared by polycondensation of dibasic acids and diamines. PA has good strength, wear resistance, heat resistance, abrasion resistance, acid and alkali corrosion resistance and self-lubrication, and is easy to process. It is particularly suitable for glass fiber and other fiber reinforcement modification. In recent years, the world's PA production capacity has grown steadily, the production scale has expanded, and companies have expanded production or built new equipment. The production capacity and output of PA are at the forefront of engineering plastics.

PEEK

PEEK is a fully aromatic semi-crystalline thermoplastic engineering plastic. Due to its high strength, high heat resistance, good dimensional stability, corrosion resistance, friction resistance, radiation resistance and other excellent properties, and can be injection molded, extruded and cut, it is widely used in aerospace aircraft and high-end civilian manufacturing industries. PEEK is a cutting-edge high-performance polymer material. Due to its superior performance, the demand for this material has steadily increased. Since its commercial production in 1978, the production capacity has been continuously improved.

PPS

PPS is a semi-crystalline polymer with a structure of benzene rings and sulfur repeatedly connected. The molecular structure is relatively simple and the density is 1.34~1.36g/cm. Because PPS has outstanding heat resistance and a heat deformation temperature of up to 260¡æ, it can be used continuously for a long time at 200~240¡æ. The mechanical properties rarely decrease at high temperatures. It also has excellent fatigue resistance and creep resistance, strong chemical corrosion resistance, excellent dimensional stability, excellent electrical properties and good molding and processing performance. It has been widely used in various industries and is recognized as the sixth largest engineering plastic and the first largest special engineering plastic after PA, polyoxymethylene, polycarbonate, polybutylene methacrylate and polyphenylene ether.

PI

PI is a polymer containing an imide ring on the main chain of the molecule, which is formed by the gradual reaction and polymerization of compounds containing dianhydride and diamine. There are many varieties of PI, but the main varieties are polyetherimide (PEI), polyamide-imide (PAl) and bismaleimide (BMI). The density of PI is 1.38~1.43g/cm. Due to the presence of aromatic heterocyclic rings with stable structure, PI has high modulus and high strength. Its tensile strength reaches more than 100MPa and its elastic modulus reaches 3~4GPa. PI has strong high temperature resistance. It can keep its main physical properties unchanged at 550¡æ for a short time and can be used for a long time at nearly 330¡æ. PI also has excellent dimensional stability, flame retardancy, chemical resistance and radiation resistance, as well as good toughness and softness. It has been widely used in aviation, aerospace, military industry, building materials, high-tech and other fields.

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