Do you really understand CPE?

- Nov 08, 2018 -

Do you really understand CPE?

CPE is chlorinated polyethylene produced by chlorination of a special high-density polyethylene, in which the hydrogen atoms in the chain of HDPE are partially replaced by chlorine atoms. White powder after drying, non-toxic.

CPE FORMULA: CH2-CHCl-CH2-CH2] N

Cpe Or CM chlorinated polyethylene (CPE) is a saturated polymer material.

Characteristics

Because CPE does not contain double chain, it has good weather resistance, better flame resistance and heat stability than PVC, low cost and excellent performance. Soluble in aromatic hydrocarbon and halogenated hydrocarbon, insoluble in aliphatic hydrocarbon, decomposes above 170 °C, gives out hydrogen chloride gas, its have stable chemical structure, excellent aging resistance, fire resistance, cold resistance, weather resistance, free coloring, chemical resistance, ozone resistance and electrical insulation, as well as good compatibility and processing Can Be mixed with PVC, PE, PS and rubber to improve its physical properties.

Three factors affecting the performance of CPE

First: the kind of PE used —— CPE obtained from high molecular weight polyethylene has higher viscosity and tensile strength, but the adhesion between CPE and PVC resin is low, and the viscosity and tensile strength of CPE obtained from low molecular weight polyethylene is low CPE prepared by high-density polyethylene process has good heat resistance and heat resistance.

Second: The size of raw material particles —— Particle size is too small to form Gel or lump CPE, too large particle size distribution of chlorine is not uniform, difficult to dissolve in organic solvents, particle size range of 0.1-200 m best.

Third: The degree of chlorination of CPE —— Chlorine content below 25% , and PVC compatibility is poor, can not be used as modifier; chlorine content more than 40% and PVC compatibility is good, can be used as a solid plasticizer, not suitable for impact modifier; CPE with 36-38% chlorine content has good elasticity and compatibility with PVC, so it is widely used as impact modifier of PVC. At present, CPE with chlorine 35% is the most widely used one. CPE with chlorine 35% has low crystallinity and glass transition temperature, good rubber elasticity and good compatibility with PVC It is widely used as impact modifier of PVC hard products.

CPE PRODUCTION TECHNOLOGY

CPE is produced by suspension method, which is divided into aqueous phase and hydrochloric acid phase. The chlorine utilization of aqueous method is high, the chlorine content of product is stable, but the equipment corrosion is serious and the waste quantity is large. Hydrochloric acid phase method is the most advanced production method, short process, stable product quality, and three low waste.

Selection of impact modifier for CPE

1) domestic CPE models are generally labeled as 135A, 135B, 140B, 239C, etc. . The first digit numbers 1 and 2 indicate the residual Crystallinity (TAC value) , 1 indicates TAC value of 0-10% , 2 indicates TAC value of 10% , the second and third digits indicate chlorine content, e.

2) The influence of Molecular Weight: the A type of CPE material has the highest molecular weight, the highest melting viscosity, the best matching with PVC, the best dispersing effect in PVC, can form the ideal network dispersion shape, so the a type of CPE material is generally chosen as the modifier of PVC.

3) TAC value: TAC value indicates the content of PE crystallization and Amorphous state in CPE, reflects the uniform distribution of chlorine atoms on CPE to some extent, TAC value is large, which indicates that PE chain section crystallizes more, but PE chain section and PVC compatibility is poor, TAC value is small, PE and PVC compatibility is good, generally select Cpe anti-impact agent with TAC value less than 5.

Effect of CPE ADDITION ON PVC

The impact strength of PVC increases quickly with the addition of CPE when the addition amount is less than 10 minutes, but the impact strength of PVC increases little when the addition amount of CPE is further increased. Therefore, as an anti-impact agent, the addition of CPE in 8-10 PHR was appropriate, and with the increase of CPE, the tensile strength of PVC blends decreased continuously and the elongation at break increased, such as the toughness expressed by the product of tensile strength and elongation at break It is obvious that the toughness of PVC will increase with the increase of CPE addition.

It is considered that CPE exceeds the saturation solubility in PVC and precipitates from PVC in more than 8 copies, forming PVC as sea, CPE is microphase separation structure of island, thus greatly improving the impact strength of PVC It has also been suggested that CPE can form a network in the formulation when it exceeds 6 PHR, and thus act as an impact modifier. However, CPE can not form a network in the formulation system when it is added in a low quantity (E. G. 1 PHR) It does not exceed the saturated solubility in PVC and has little impact on the formulation.

Effect of CPE ON PROCESSING PROPERTIES OF PVC

The addition of CPE was delayed plasticizing when the content of CPE was less than 5 PHR, and had little effect on plasticizing of Formula System when the content of CPE was 5 phr. With the increase of CPE content, the plasticizing time became shorter, the maximum plasticizing torque and equilibrium plasticizing torque increased, and the plasticizing temperature decreased.

The chlorine content of CPE is 35% . There are two segments in the structure of CPE: chlorinated segment with hydrogen atoms replaced by chlorine atoms, which has strong structure and good compatibility with PVC, and PE segment with hydrogen atoms not replaced by chlorine atoms The structure polarity of this section is very weak, poor compatibility with PVC, between the external lubrication, can delay the plasticization of PVC.

The glass transition temperature of CPE is about 10 °C, and that of PVC is about 80 °C. under the test conditions, CPE shows the tendency of softening earlier than PVC and slightly higher viscosity. When the addition of CPE is less, the total amount of polar segments with good compatibility with PVC is less With the increase of CPE, the advance softening of a large number of CPE molecules and the higher viscosity of CPE promote the increase of the viscosity of the formulation system The effect of CPE on the viscosity of bulk material overcomes the external lubrication effect of Pe chain in the structure of bulk material, makes the whole formulation begin to plasticate at lower temperature, and promotes the plasticization of bulk material.