Brief introduction to UPVC drainage pipe formula design and its common stabilizers

UPVC, also known as rigid PVC, is an amorphous thermoplastic resin prepared by polymerization of vinyl chloride monomer and then added with certain additives (such as stabilizers, lubricants, fillers, etc.).

Hard polyvinyl chloride drain

Advantages: light weight, corrosion resistance and high strength.

Disadvantages: high melt viscosity and poor fluidity.

UPVC hard tube formula

PVC ( SG-5) + plasticizer + stabilizer (lead salt, metal soap) + lubricant + processing aid.

UPVC common stabilizer

1, lead salts

Most commonly used, but not for non-toxic and transparent products.

Commonly used tribasic lead sulfate (tribasic lead sulfate) and dibasic lead phosphite (lead dibasic phosphite)

Principle of action: The salt-based lead salt inhibits its autocatalysis by capturing the detached hydrogen chloride.

Tribasic lead sulfate

White or slightly yellow powder. It is discolored in daylight, sweet and toxic! Do not dissolve in water, soluble in hot acetic acid amine solution. Unstable can decompose on its own. Must be stored, melting point 820 °C, excellent thermal stability and electrical properties. The main PVC stabilizer has a long-lasting stabilizing effect, and has synergistic effect with the dibasic lead phosphite. It is susceptible to sulfide contamination and should be avoided in combination with sulfide.

Dibasic lead phosphite

White or yellowish powder, sweet. The relative density is 6.94. The refractive index is 2.25. Soluble in hydrochloric acid, nitric acid, ammonium acetate solution is insoluble in water and organic solvents. It turns grayish black at around 200 °C; it turns yellow at around 450 °C.

(1) organotins

Good stability, transparent, toxic or non-toxic, limited use due to high price.

(2) Metal soaps

Stable effect is general, transparent, toxic or non-toxic, rarely used alone, often used in combination, often used in soft products.

(3) Rare earths

The new variety has the advantages of transparency and non-toxicity, and has great development prospects.

2, plasticizer

The plasticizer is added to only 5 parts or less of the hard product, and 25 parts or less of the soft product. Ideal performance: good compatibility with resin; high plasticizing efficiency; stable to heat and light, low volatility; colorless, odorless, non-toxic; water, oil and organic solvent extraction; flame retardant, electrical insulation Good properties; viscous paste viscosity stability; cheap; plasticizer added to the polyvinyl chloride resin, the greater the proportion of added, the softer the plastic products: when the amount is less than 5%, the plastic products are hard; When the amount is 15% to 25%, the plastic product is semi-rigid; when the amount is more than 25%, the plastic product is soft; when the plasticizer is added in an amount of 5% to 15%, anti-plasticization occurs. Affect the quality of the product and should be prevented as much as possible during preparation.

Common PVC main plasticizer

DOP Dioctyl phthalate (good compatibility, good light stability, good electrical insulation, low temperature resistance, non-toxic);

DBP dibutyl phthalate (good compatibility, softness, low cost, not just use);

DIDP diisodecyl phthalate (good heat resistance, good electrical insulation).

Auxiliary plasticizer

Dioctyl adipate DOa (good temperature, poor formability);

Dioctyl sebacate DOS (good temperature, poor formability);

Epoxidized soybean oil EOS (good thermal stability, low volatility, non-toxic);

Chlorinated paraffin 42% (flame resistant, good electrical performance, low cost, not only used).

3, lubricant

The PVC melt tends to adhere to the metal, and the friction between the melt and between the melt and the processing equipment is large, and a lubricant needs to be added to overcome the frictional resistance. The amount of lubricant added is relatively large. According to the compatibility of lubricant and PVC resin, it can be divided into internal lubricant (good compatibility) and external lubricant (poor compatibility).

(1) Metal soaps (external lubricants)

Metal salts of higher fatty acids (commonly known as metal soaps) are one of the commonly used lubricants. In addition to lubrication, it is also a heat stabilizer for PVC. For a saponified metal, the longer the carbon chain of the fatty acid to be bonded, the better the lubricity. Commonly used are calcium stearate, zinc stearate, lead stearate, etc., of which lead stearate has the best lubricity.

(2) Polyethylene wax (internal lubricant)

PE wax, also known as polymer wax, is a lubricant with stable chemical properties and good electrical properties. Polyethylene wax has a stronger internal lubrication than other external lubricants for PVC.

4, filler

Also known as fillers, fillers. A solid substance added to a material to improve performance or reduce cost. Organic, inorganic, metallic or non-metallic powders which are generally free of water, neutral and which do not adversely affect the composition of the materials can be used as fillers.

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