Issue 35/2012 - Advances in neoprene production technology

Neoprene is an elastomer
prepared by homopolymerization or copolymerization reaction with 2-chloro-1,3-butadiene as the main monomer.
The progress of production technology is mainly reflected in the improvement of polymerization process, "three wastes" treatment and new product development, in order to further expand the application field
.

1 Polymerization process and post-treatment

In the polymerization process, DuPont shifted from a single-loop control system to a computerized distribution control system, using a touch screen to adjust the speed of the polymerization kettle agitator, the initiator flow rate and the temperature of the emulsion and cooling brine, improving the initiator flow control and emulsion temperature control, making the process more stable and significantly improving
Mooney viscosity control.

In the post-treatment of neoprene, a breakthrough has been made by spiral extrusion dehydration drying technology
.
The neoprene latex and coagulant enter a specially designed screw extruder at the same time, and the agglomerated latex is removed by back pressure in the dewatering section of the extruder
.
Compared with the frozen drum coalescing-layer hot air drying technology, spiral extrusion dehydration drying technology has great improvements
in energy consumption and labor intensity.
This technology has been developed to handle neoprene varieties
with poor frozen film-forming and banding.

Neoprene products have good stability and aging resistance, but the storage stability of raw rubber is poor, and it will be oxidized during storage to produce spontaneous crosslinking
.
To ensure the long-term performance of neoprene, effective antioxidants
must be added.
At present, domestic neoprene generally uses polyphenols or aromatic amine antioxidants, such as antioxidant-264, 1010, KY405, etc.
, the principle is to delay or prevent oxidation by capturing free radicals, but can not completely stop
oxidation.
From the perspective of aging mechanism, the most ideal anti-aging system is composed of antioxidants and hydroperoxide homolysis inhibitors (that is, auxiliary antioxidants), the latter accelerates the decomposition of a small amount of peroxide, which can improve the effect of phenolic antioxidants, commonly used auxiliary antioxidants mainly include phosphite, thioesters, etc
.
Researchers from Shanxi Synthetic Rubber Group Co.
, Ltd.
studied the stability effect
of trinonylphenyl phosphite (TNP) during the storage of neoprene raw rubber.
The experimental results show that the minimum dosage of the main antioxidant antioxidant 264 is 1.
3phr with 0.
3phr
TNP.
From the comprehensive consideration of protection effect and economy, the appropriate dosage of antioxidant 264 is 1.
5~1.
7phr, and the use of TNP can improve the aging resistance of neoprene, but the processing cost remains basically unchanged
.
The type of phenolic antioxidant is replaced from antioxidant 264 to 1010 or 2246, and TNP can improve the anti-thermal oxygen aging performance of neoprene, but the cost is slightly higher, and it can be selected
according to the specific use and use requirements of the product.

Through the degassing treatment of bonded neoprene, the residual amount of unreacted monomer can be reduced, thereby reducing the later volatilization of neoprene and meeting the requirements of
safety and environmental protection.
In addition, through the recycling of unreacted monomers in neoprene, the stability, balance and polymerization cycle
of latex can be improved.
At present, almost all the latex degassing methods used by neoprene manufacturers in the world are steam direct heating latex and two-stage vacuum flash type
.
Shanxi Synthetic Rubber Group Co.
, Ltd.
draws on the degassing technology of ordinary neoprene rubber latex and refers to the Tubular Degassing process route of DuPont Company of the United States, and establishes a production process using the secondary tubular degassing method, namely the primary recovery monomer and the secondary flash concentration and the degassing rate of more than
85%.

2 "Three wastes" treatment

The production of neoprene in China adopts calcium carbide method, which will produce a large number of high-concentration organic wastewater, which is highly toxic and contains acetylene, acetaldehyde, chloroprene, benzene, chlorobenzene, copper and other harmful substances, which is a kind of industrial wastewater
with serious pollution and great difficulty in treatment.
In recent years, the research on the treatment of industrial wastewater by sequential batch reactor (SBR) has attracted extensive attention
.
Researchers from Shanxi University used SBR-filtration-adsorption to treat
neoprene production wastewater.
The results show that using SBR-anthracite coal-quartz sand double-layer filter material filtration-activated carbon adsorption process, when the COD of the influent water is about 1020mg/L, the COD of the effluent is reduced to less than 40mg/L, the turbidity is reduced to 0.
75NTU, the color is reduced to 0, and the effluent can be reused for production
.

3 New product development

In terms of new product development, great progress has been made at home and abroad, and a variety of new products
with a wide range of applications have been researched and developed.

Because neoprene is inferior to saturated rubber such as ethylene propylene rubber and chlorosulfonated polyethylene due to its heat resistance, it is constantly being replaced
by saturated rubber in many applications.
However, hydrochloroprene has good low temperature resistance and ozone resistance, which is very suitable for the manufacture of hoses, tapes, gaskets, seals and shockproof rubber products
.
The hydrogenation of neoprene rubber adopts a homogeneous catalytic process with triphenylphosphine rhodium chloride/triphenylphosphine
chloride.
Hydrochloroprene exhibits some unique properties after oxide vulcanization, suitable for the manufacture of high-performance industrial rubber products, especially automotive rubber parts and anti-vibration rubber products
for construction projects.
The hydroneoprene on the market now includes DCR32, Denka Chloroprene M70, Denka Chloroprene S40 and so on
.
The performance of hydrogenated neoprene rubber is related to the variety of raw materials and the degree of hydrogenation, the higher the degree of hydrogenation, the better the heat resistance, but the cold resistance and ozone resistance decrease
.
It is worth noting that the vulcanization of hydrogenated neoprene is more difficult than that of ordinary neoprene, and special vulcanization formulations are required, such as peroxide vulcanization systems
that are less commonly used in ordinary neoprene vulcanizates.

High Mooney viscosity neoprene rubber has excellent cohesion energy, widely used in rubber adhesives and high fill rubber products, foreign high Mooney viscosity neoprene rubber products are Neoprene WHV 100, Neoprene WHV, Bayer243, Bayer253, Denka M139L, Denka M130H and so on
。 The researchers of Shanxi Synthetic Rubber Group Co.
, Ltd.
adopted a control process that combined the polymerization formula with the termination at the appropriate conversion rate, which not only obtained a finished glue with stable performance, but also adapted to the existing production process
。 In the presence of 4phm (the best emulsification system formula) disproportioned rosin, 0.
5phm stearic acid, 0.
35phm sodium lauryl sulfate, 0.
5phmLomar PW emulsification system, 2-chloro-1,3-butadiene was polymerized by using a regulator under the conditions of water/oil mass ratio of 1.
05 and 38~42 °C, and a high Mooney viscosity neoprene
with a similar quality to similar foreign products was obtained 。 The use of 2-chloro-1,3-butadiene monomer with a purity greater than 97.
5% to control the monomer conversion rate at 83%~87% is conducive to improving the storage stability
of high Mooney viscosity neoprene.

In order to improve the thermal stability of neoprene, Bayer has developed a copolymer of chloroprene with carboxyic acid amide, carboxylic anhydride and/or carboxylic acid monomer (low gel type and high gel type), which can be used
as a modifier in combination with neoprene.

DuPont has introduced a series of directly soluble bonded neoprene, which has better adhesion performance than traditional varieties, and has better
spray and brush properties.
By eliminating the need for pre-plasticizing, adhesive formulation time can be reduced by approximately 40%.

Due to the different viscosity grades, the effective time, solubility and solvent dosage of the adhesive bonding can be controlled
.
DuPont has also developed highly elastic, heat-resistant neoprene for the manufacture of automotive engine mounts suitable for use with sulfur-regulated neoprene; Developed bonded neoprene latex with good heat resistance and strong initial adhesion; Developed ethyl methacrylate, hydroxyethyl methacrylate grafted neoprene rubber and methyl methacrylate grafted neoprene latex that
do not change color.

Nippon Electrochemical Corporation has developed neoprene with high rigidity and tear strength, shock-absorbing neoprene, anti-blocking waterproofing membrane pre-coated adhesive, and neoprene with high rigidity and good moldability
.
In order to adapt to the development of adhesives to water-based types, carboxylated neoprene latex (Denka Chloroprene 115)
was also developed.

Researchers from South China University of Technology and Chongqing Changshou Chemical Co.
, Ltd.
jointly developed a preparation method
for powder neoprene and granular neoprene.
The emulsifier aqueous solution of monovalent metal salt is added to the neoprene latex, and powder neoprene and granular neoprene particles are prepared by heat treatment, agglomeration and hardening steps, and then filtered, washed, dehydrated and dried to obtain a finished product
with stable storage and good fluidity with a particle size distribution of less than 1.
0mm for the former and a particle size distribution of 1.
0~5.
0mm for the latter.
The coating on the surface of powder neoprene and granular neoprene particles prepared by this method is the coating isolatant generated during the preparation process, and the coating effect is good
.
By adjusting the coalescing conditions, a variety of powder neoprene and granular neoprene that meet the requirements of the current national standards can be prepared with different particle size
distributions.