CPE, namely chlorinated polyethylene, is prepared by chlorination of special high-density polyethylene (HDPE). It is the product of partially replacing hydrogen atoms on HDPE molecular chain with chlorine atoms. After drying, it is white powder, non-toxic.
CPE molecular formula: CH2-CHCl-CH2-CH2] n
English abbreviation: CPE or CM chlorinated polyethylene (CPE) is a saturated polymer material.
characteristic
Because CPE molecule does not contain double chains, it has good weather resistance, flame resistance and thermal stability, superior to PVC, low cost and excellent performance. It is soluble in aromatic hydrocarbons and halogenated hydrocarbons, insoluble in aliphatic hydrocarbons, decomposes above 170 ℃ and emits hydrogen chloride gas. It has stable chemical structure, excellent aging resistance, flame resistance, cold resistance, weather resistance, free coloring, chemical resistance, ozone resistance, electrical insulation, and good compatibility and processability. It can be mixed with PVC, PE, PS, and rubber to improve their physical properties.
Three factors affecting CPE performance
First, the type of PE used ---- CPE obtained from high molecular weight polyethylene has high viscosity and tensile strength, but the adhesion between CPE and
PVC Resin is low. CPE obtained from low molecular weight polyethylene has low viscosity and tensile strength. CPE obtained from high density polyethylene has good heat resistance.
Second: size of raw material particles ---- gel or agglomerated CPE is easy to form when the particle size is too small, chlorine distribution is uneven when the particle size is too large, and it is difficult to dissolve in organic solvents, and the particle size range is 0.1-200 μ M is the best.
Third: The chlorination degree of CPE ---- When the chlorine content is below 25%, the compatibility with PVC is poor, and it cannot be used as a modifier; When the chlorine content is more than 40%, it has good compatibility with PVC, and can be used as a solid plasticizer, not suitable for
Impact Modifier; CPE with chlorine content of 36-38% has good elasticity and compatibility with PVC, so it is widely used as impact modifier of PVC. At present, the most widely used CPE is the one containing 35% chlorine. The CPE containing about 35% chlorine has low crystallinity and glass transition temperature, good rubber elasticity, and suitable compatibility with PVC. It is widely used as an impact modifier for PVC hard products.
CPE production technology
CPE is mainly produced by suspension method, which is divided into aqueous phase method and hydrochloric acid phase method. The water phase method has high chlorine utilization rate and stable chlorine content in the product, but the equipment is severely corroded and the amount of three wastes is large. Hydrochloric acid phase method is the most advanced production method with short process, stable product quality and low waste.
Selection of CPE impact modifier
1) Domestic CPE models are generally identified by 135A, 135B, 140B, 239C, etc. The first digit 1 and 2 indicate the residual crystallinity (TAC value), 1 indicates that the TAC value is 0-10%, 2 indicates that the TAC value is>10%, and the second and third digits indicate the chlorine content. For example, 35 indicates that the chlorine content is 35%, and the last digit is the letter ABC, which is used to indicate the size of PE molecular weight of raw materials. A is the maximum, and C is the minimum.
2) Influence of molecular weight: CPE type A material has the largest molecular weight and large melt viscosity. Its viscosity matches PVC best. It has the best dispersion effect in PVC and can form an ideal network dispersion form. Therefore, CPE type A material is generally selected as the modifier of PVC.
3) TAC value: TAC value indicates the content of PE crystal and amorphous form in CPE molecule, which reflects the uniform distribution of chlorine atoms on CPE molecule to some extent. A large TAC value indicates that the PE chain segment has more crystals, while the compatibility between PE chain segment and PVC is poor. A small TAC value indicates that the compatibility between PE and PVC is good. Generally, CPE with a TAC value less than 5 is selected as the impact agent.
Effect of CPE addition on PVC
The impact strength of PVC increases rapidly with the addition of CPE when the amount of CPE is less than 10 points, but the impact strength of PVC increases little when the amount of CPE is further increased. Therefore, as an impact resistant agent, it is appropriate to add 8-10 phr of CPE. At the same time, with the increase of CPE, the tensile strength of PVC blends continues to decline and the elongation at break increases. If the toughness is expressed by the product of tensile strength and elongation at break, the PVC toughness will obviously increase with the increase of CPE addition.
Some literatures think that when more than 8 portions of CPE exceed the saturated solubility in PVC and precipitate from PVC, forming a micro phase separation structure of PVC as sea and CPE as island, which greatly improves the impact strength of PVC. Others think that when more than 6 portions of CPE are added, a network can be formed in the formula, which plays an impact modification role. However, when the amount of CPE is low (such as 1 portion), a network cannot be formed in the formula system, It will not precipitate beyond its saturated solubility in PVC, and it has little impact modification effect in the formula.
Effect of CPE on processing properties of PVC
When the number of CPE added is less than 5, the plasticization is delayed, and at 5, it has no effect on the plasticization of the formula system. It plays a role in promoting plasticization when CPE exceeds 5 phr. With the increase of CPE, the plasticizing time of the formula becomes shorter and shorter, the maximum plasticizing torque and balance torque increase, and the plasticizing temperature decreases gradually.
The chlorine content of CPE is 35%, and there are two chain segments in its structure: one is the chlorination chain segment whose hydrogen atom is replaced by chlorine atom, which has a strong structure and is similar to PVC with good compatibility; the other is the PE chain segment whose hydrogen atom is not replaced by chlorine atom, which has a weak structural polarity and poor compatibility with PVC, which plays an external lubrication role between PVC and can delay the plasticization of PVC.
The glass transition temperature of CPE is about 10 ℃, while that of PVC is 80 ℃. Under test conditions, CPE shows a trend of softening and plasticizing earlier than PVC and a slightly higher viscosity. When the amount of CPE added is small, the total amount of polar segments with good compatibility between CPE and PVC is small, the external lubrication of PE segments is dominant, and the plasticization of the delayed system. With the increase of CPE, a large number of CPE molecules become soft and plasticized in advance and the higher viscosity promote the viscosity of the entire formula system to increase, At this time, the influence of CPE on the viscosity of the whole material overcomes the external lubrication of the PE chain segment in its structure, so that the entire formula system begins to plasticize at a lower temperature, which promotes the plasticization of the material.
Application of CPE
1. The application of CPE enhanced PVC waterproof coiled materials in waterproof coiled materials, due to the excellent characteristics of CPE, the tensile strength of the new product has been increased by 80%, the tear strength has been increased by 50%, and its mechanical weather resistance, low temperature resistance, aging resistance and other properties have been improved. It is well received by the construction department (including 10% - 15% CPE). Neoprene CPE waterproof coiled materials and neoprene CPE styrene butadiene rubber waterproof coiled materials have the advantages of high strength, high elasticity, high elongation, corrosion resistance, high temperature resistance, cold resistance, aging resistance, flame retardancy, etc. They are ideal waterproof materials of a new generation and have a broad market.
2. The production of plastic doors and windows by blending CPE and PVC has greatly improved its elasticity, toughness and low-temperature performance, and has good weather resistance, heat resistance and chemical stability. This kind of plastic doors and windows is cheap, corrosion-resistant, colorful and bright. It has more advantages than aluminum alloy doors and windows. It has replaced aluminum doors and windows to a large extent, and the market will become wider and wider.
3. Application in wire and cable sheath: The addition of CPE can improve its cathodic combustion performance, anti-aging performance and physical and mechanical properties. It can also be used as the main body to make wire and cable coating materials with excellent performance.
4. Adding CPE elastomer into PE can improve its printability, flame resistance and flexibility. When 5% CPE was added to HDPE, the adhesion between the obtained mixture and the ink was increased by three times. The PE hose for mining has good flame retardancy after adding CPE.
5. Application of CPE as main material: It can be used to manufacture rubber hoses with good performance of oil resistance, acid resistance, folding resistance, ozone resistance and Freon resistance. It is suitable for manufacturing hydraulic rubber hoses, cooler rubber hoses, fuel rubber hoses, etc. The cow like leather sole made with CPE as the main body has excellent performance.
6. Application of CPE in transmission belt: heat resistant transmission belt can be manufactured, and it also has good resistance to nonpolar solvent swelling. The adhesion and bending times between each adhesive layer of the transmission belt produced with CPE/NR/SBR adhesive are higher than those of the transmission belt made with pure adhesive, thus extending the service life. At the same time, it also improves the large shrinkage of the pure adhesive after calendering, and the poor permeability of the adhesive in textiles during calendering The molding belt embryo is easy to stick, which improves the weather resistance and flame retardancy of the transmission belt.
7. Blending of CPE with other rubbers: CPE has good compatibility with a variety of rubbers. When CPE and NR are blended, their wear resistance, fatigue resistance, acid resistance and alkaline resistance become better. Compared with NBR and CR, the price of CPE is lower. CPR and NBR can be used to make oil resistant rubber hose and oil resistant sealing products because of their oil resistance and excellent heat and oxygen aging resistance.
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