General overview of chlorinated polyethylene, vulcanization systems, compounding systems and an introduction to their application

General overview of chlorinated polyethylene, vulcanization systems, compounding systems and an introduction to their application
General overview of chlorinated polyethylene, vulcanization systems, compounding systems and an introduction to their application

Chlorinated polyethylene waterproof membrane

1. Understanding Chlorinated Polyethylene

Chlorinated polyethylene is a new type of elastomeric material synthesized by chlorination of high density polyethylene. According to content of chlorine, residual crystallinity and other technical indicators, chlorinated polyethylene products can be divided into chlorinated rubber products. chlorinated polyethylene (XM) and chlorinated resin-type polyethylene (CPE). When mass fraction of chlorine is from 30% to 40%, it will exhibit properties of an elastomer.

1.1 Difference between chlorinated polyethylene rubber (CM) and chlorinated polyethylene resin (CPE)

The chain of CM macromolecules contains a large number of randomly arranged chlorine atoms, regularity of molecule is low, and flexibility of macromolecules is increased, as a result of which CM exhibits characteristics of rubber;

The content of chlorine atom in CPE macromolecule itself is small and distributed in blocks, so that CPE molecule will have a long methylene chain segment, and macromolecule has a certain degree of regularity, which promotes formation of crystallization, so that CPE has a certain rigidity.

Chlorinated polyethylene made from HDPE low pressure polyethylene has better resistance to high temperature heat aging than chlorinated polyethylene made from high pressure polyethylene. Typically, for production of chlorinated polyethylene, polyethylene with a density of 0.93-0.96 g/cm3, an average molecular weight of 50,000-250,000 and a melt index of 0.01-2.0 g/10 min is used.

The degree of chlorination of chlorinated polyethylene has a great influence on its characteristics. Less than 15% chlorine is plastic, 16–24% chlorine is thermoplastic elastomer, 25–48% chlorine is rubber-like elastomer, and 25–48% chlorine is rubber. chlorine content 49-58%, similar to leather It is a semi-elastic hard polymer, at up to 73% chlorine it becomes a brittle resin.

When introducing about 27% chlorine into high pressure polyethylene, crystallization will completely disappear, and into high-density polyethylene with a higher crystallinity - about 30% chlorine, and crystallization will also completely disappear. The chlorine content of elastic rubber body is preferably 30 to 40%.

The chlorine content of commercial chlorinated polyethylene rubber is generally in range of 25-45%. As a rule, with an increase in chlorine content, oil resistance, gas permeability and fire resistance are improved; with a decrease in chlorine content, frost resistance, elasticity and resistance to bending under compression are improved.

General overview of chlorinated polyethylene, vulcanization systems, compounding systems and an introduction to their application

Chlorinated Polyethylene CPE/CM Performance Index

1.2. What are obvious properties of chlorinated polyethylene

Chlorinated polyethylene is a saturated polymer material, appearance of which is white powder, non-toxic and tasteless, it has excellent weather resistance, ozone resistance, chemical resistance and aging resistance, and has good oil resistance, fire resistance and staining resistance. Good impact strength (remains flexible at -30°C), good compatibility with other polymeric materials, high decomposition temperature, decomposition to form HCl, HCL can catalyze dechlorination reaction of CPE.

1.3. Characteristics of chlorinated polyethylene

①CPE is a saturated rubber with excellent resistance to heat aging, oxygen aging, ozone aging, acid and alkali resistance and chemical properties.

CPE has excellent oil resistance, among which excellent ASTM No. 1 and ASTM No. 2 oil resistance comparable to NBR, excellent ASTM No. 3 oil resistance, better than CR and comparable to CSM.

③CPE contains chlorine, which has excellent flame retardant properties and burns without dripping. It can be combined with antimony-based fire retardant, chlorinated paraffin and Al(OH)3 in a suitable ratio to obtain a fire retardant material with excellent fire retardant performance and low cost.

④CPE is non-toxic, free of heavy metals and PAHs, and fully complies with environmental protection requirements.

CPE has high filling efficiency and can produce products that meet different performance requirements. CPE has good processability, Mooney viscosity (ML121 1+4) is in range of 50-100, and there are many grades to choose from.

1.4 Chlorinated polyethylene development history

In 1960s, German company Hoechst successfully developed and implemented industrial production for first time. my country started developing chlorinated polyethylene in late 1970s. "Aqueous phase slurry synthesis of CPE technology" was first successfully developed by Anhui Chemical Industry Research Institute, and production plants with a capacity of 500-1000 tons/year with various scales were built in Wuhu, Anhui, Taicang, Jiangsu and Weifang, Shandong. . In early 1990s, Shandong Weifang Chemical Plant introduced a 6,000 ton complete set of CPE production equipment from Germany. In beginning, it produced resin-type chlorinated polyethylene, which was mainly used as an impact modifier for PVC and a flame retardant modifier for engineering plastics such as ABS.

In China, Yaxing Chemical (Weifang) has an annual output of 120,000 tons of CPE typerubber and resin. It is largest chlorinated polyethylene manufacturer in Asia. The performance of product is stable and quality is excellent. The trade name is Weiprene., main grades are 135A, 135B and so on. Internationally, at end of 2005, Dow Chemical (Dow Chemical) acquired CPE product line of original Dupont Dow Elastomer (DDE) Chemical, which has superior performance. Trade name Tyrin, but main product brand Tyrin CM0136, Tyrin CM0636 wait.

Second, Chlorinated Polyethylene Curing System

Chlorinated polyethylene is a saturated rubber that cannot be effectively cured with conventional sulfur curing systems. The vulcanization system is divided into four main vulcanization systems:

① Thiourea system, ② Peroxygen system, ③ Thiadiazole system, ④ Dimercaptoamine triazole salt system.

2.1. Thiourea

The former application of chlorinated polyethylene vulcanization system is thiourea system, most effective of which is Na-22, but Na-22 has a slow vulcanization rate, poor aging performance, high compression set, and Na-22 is a serious carcinogen and emits an unpleasant odor when vulcanized. Its use is restricted abroad.

2.2. Peroxygen System

At this stage, application of chlorinated polyethylene vulcanization system is more mature than application of peroxide vulcanization system, which has a faster vulcanization rate, good physical properties of products, and small compression set. The peroxide system can be used in production of tapes, and products have good physical properties, heat resistance and oil resistance. When combining system, addition of auxiliary cross-linking agents, such as TAIC, TATS, TMPTM, GVA-2, can significantly improve its physical and mechanical properties and heat resistance. Because peroxide is a free radical cross-linking reaction, some acidic excipients will interfere with free radical formation, so such excipients should not be used. However, peroxide is not suitable for low-pressure shapeless vulcanization and has high processing requirements, so it is difficult to use in most rubber product manufacturing processes.

2.3. Thiadiazole system

EataMixTCHC is a non-toxic composite curing agent for chlorinated polyethylene. TCHC can use cheap aromatic oil as a plasticizer, and vulcanizate has excellent performance. The activity of MgO has little effect on physical and aging properties of vulcanized rubber in TCHC system.with an iodine absorption value of 150, and can replace expensive imported high-activity magnesium oxide, greatly reduce production costs.

The application cost is much lower than foreign thiadiazole systems, and it can be applied in various vulcanization processes, including low temperature, moldless vulcanization, no pressure vulcanization and low pressure vulcanization. The vulcanization rate of rubber compound in this system is high, physical properties of vulcanized rubber are excellent, compression set is low, thermal oxygen resistance, ozone aging and oil resistance are good, and it is also effective. rubber hoses. The vulcanization rate of TCHC is lower than that of peroxide, but it can be vulcanized at a lower temperature, without pressure and without mold, and vulcanizate has excellent performance.

2.4. Triazole dimercaptoamine salt system

The triazole dimercaptoamine vulcanizing agent is a single substance that combines effective groups of a thiadiazole vulcanizing agent and an accelerator (n-butyraldehyde and aniline condensate) that overcomes effect of thiadiazole and accelerator on rubber crosslinking. Finally, uneven distribution of bonds makes rubber-stitched body a stable structure. Compared to thiadiazole system, salt also changes pH of system by introducing special groups, from strong acidity to neutrality, changing adverse effect of acidic excipients on system, making rubber more reactive when crosslinked. . Therefore, crosslinked chlorinated polyethylene rubber of this system has a qualitative improvement in physical properties or chemical properties. Aromatic oil, magnesium oxide and magnesium hydroxide can be used as raw materials, suitable for low temperature conditions of vulcanization process without pressure and low pressure, high vulcanization speed, faster than thiadiazoles, less additives, favorable unit price, no decomposition within vulcanization temperature range and odorless, environmental protection and non-toxic.

Third Chlorinated Polyethylene Coordination System

3.1. Strengthening filling system

Chlorinated polyethylene is a non-self-reinforcing rubber that requires a reinforcing system to achieve good strength. Its reinforcing filler system is similar to that of general purpose rubber. The reinforcing agent is mainly composed of carbon black and silica. Bonding vinyl to frame. Chlorinated polyethylene has high filling properties, and filling system mainly includes calcium carbonate, talc, clay, etc.

3.2. Plasticizing system

Ester-based plasticizers and aromatic-based plasticizersHydrocarbons are most commonly used plasticizers for chlorinated polyethylene, such as dioctyl terephthalate (DOTP), dioctyl adipate (DOA), trioctyl trimellitate, aromatic oil, etc., their solubility parameters are close to CM. and they have good compatibility. Production of dioctyl phthalate (DOP) has been discontinued due to environmental concerns. The use of DOA and DOS in a rubber compound can endow rubber compound with excellent cold resistance, and DOS is very suitable for situations where both heat resistance and low temperature resistance are required.

3.3. Stable protection system

Chlorinated polyethylene releases hydrogen chloride when heated or cured (peroxide-free curing system), so acid absorbing stabilizers such as calcium stearate, barium stearate, tribasic lead sulfate, or magnesium oxide should be used in formulation. .

Brother Toughness Note: Some customers also use Renprene TPV + CPE. Because there is no stable protection system, they find that they burn out during injection molding, and injection molding temperature is only 170 ° C. 180°C.

Fourth, use of chlorinated polyethylene

In production of thermoplastic resins, CPE can be used not only alone, but also with polyvinyl chloride (PVC), polyethylene (PE), polypropylene (PP), polystyrene (PS), ABS and other resins, and even polyurethane. (PUR) mixed use.

In rubber industry, CM can be used as a high performance high quality specialty rubber, and with ethylene propylene rubber (EPR), butyl rubber (IIR), nitrile rubber (NBR), chlorosulfonated polyethylene (CSM) and other rubber compounds.

Chlorinated polyethylene can be used as a modifier for PVC, ABS and other polyolefins, can improve toughness of PVC and improve printability and fire resistance of vinyl, is used to produce non-flammable and chemical resistant floor materials, artificial leather, panels, etc. Can be used to improve strength and fire resistance of adhesives. It can also be used in production of foams, films, sheets, laminates, etc.

General overview of chlorinated polyethylene, vulcanization systems, compounding systems and an introduction to their application

Chlorinated polyethylene microporous foam

Chlorinated polyethylene can not only be used as an impact modifier for hard PVC products, but also widely used in production of plastic windows and doors and pipes, and as a special rubber to replace neoprene in wire and cable and hose tape industries.

Source: Macromolecule Network and other unknown early authors organized by Brother Tough Team

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