PP

Polypropylene (Polypropylene), referred to as PP, is commonly known as pleated plastic.

Classified by crystallinity: isotactic PP (crystallinity is as high as 95% or more, molecular weight is 80,000-150,000)

Random PP (non-crystalline at room temperature, molecular weight 0.3-10,000, less application)

Characteristics and applications of polypropylene (PP)

1. Polypropylene characteristics:

(1) Physical properties:

a. Non-toxic, odorless, tasteless, semi-transparent or transparent particles (powder milky white);

b. Density: 0.90～0.91g/cm3;

c. Stability to water: the water absorption rate in 24h in water is only 0.01%;

d. Molecular weight: between 80,000 and 150,000;

e. Good formability, large shrinkage, thick-walled products are easy to dent;

f. Good gloss and easy to color.

(2) Mechanical properties:

a. High crystallinity and regular structure: the strength, hardness and elasticity are higher than HDPE;

b. At room temperature and low temperature: high structural regularity, poor impact strength (when the molecular weight increases, the impact strength also increases);

c. Bending fatigue resistance: If a PP injection-molded one-piece living hinge is used, it can withstand 7x107 times of opening and closing folding and bending without any trace of damage;

d. Dry friction coefficient: The dry friction coefficient of PP can be comparable to PA6 (under oil lubrication, it is not as good as PA6).

(3) Thermal performance:

a. Melting point: 164～170℃,

b. Heat resistance: It can be disinfected and sterilized at a temperature above 100°C, and will not deform at 150°C without external force.

c. Embrittlement temperature: -35℃ (cold resistance is not as good as polyethylene).

(4) Chemical stability:

a. Chemical stability: In addition to being corroded by concentrated sulfuric acid and concentrated nitric acid, it is relatively stable to other chemical reagents;

b. Softening and swelling: low molecular weight aliphatic hydrocarbons, aromatic hydrocarbons and chlorinated hydrocarbons can soften and swell PP;

(The chemical stability increases with the increase of crystallinity. This property is suitable for making various chemical pipelines and fittings, and has good anti-corrosion effect).

(5) Electrical performance:

a. High-frequency insulation performance: excellent (almost no water absorption, insulation performance is not affected by humidity);

b. Dielectric coefficient: 2.0～2.5 (heated electrical insulation products);

c. Breakdown voltage: 40KV/mm;

d. Arc resistance: 130s (high static electricity, easy to aging in contact with copper).

(6) Weather resistance:

a. Photoaging: PP is sensitive to ultraviolet (UV);

b. Thermal oxygen aging: Heat and oxygen will accelerate PP aging.

2. Polypropylene use:

(1) Film products: PP film products are transparent and shiny, with little permeability to water vapor and air:

a. Blown film;

b. Cast film (CPP);

c. Biaxially stretched film (BOPP).

(2) Injection molded products: can be used for engineering accessories such as automobiles, electrical, machinery, meters, radios, textiles, and national defense, daily necessities, turnover boxes, medical and health equipment, and building materials.

(3) Extruded products: can be used as pipes, profiles, monofilaments and fishing ropes. Packing straps, strapping ropes, woven bags, fibers, composite coatings, sheets, plates, etc. Blow-molded hollow molded products, various small containers, etc.

(4) Others: low foaming, calcium plastic board, synthetic wood, laminate, synthetic paper, high foaming can be used as structural foam.

Modification of isotactic PP (molecular weight 80,000 to 150,000)

Polypropylene can be modified by filling, reinforcement, blending, copolymerization, and crosslinking.

1. Adding calcium carbonate, talcum powder, inorganic minerals and other fillers can improve rigidity, hardness, heat resistance and dimensional stability;

2. Adding glass fiber, asbestos fiber, mica, glass beads, etc. can increase the tensile strength, and improve the creep resistance and low temperature impact resistance;

3. Adding elastomers and rubbers can improve impact performance, transparency, etc.;

4. Adding carbon fiber (CF) can increase the strength, especially the flexural modulus.