Chloroprene rubber

Introduction:

It is the first synthetic rubber developed commerically.In terms of consumption polychloroprene has become a most important speciality rubber for non tyre application

Special properties: excellent flame resistance

Properties:

Good ozone resistance
Good flame resistance

History if CR

The polychloroprene story started in 1925 with the synthesis of the monomer.

1938-  DuPont began marketing the polymer as neoprene.

1940-  Development of copolymer with sulfur made

1950-  Soluble sulfur free mercaptan modified grades were introduced.

1960- pre cross-linked grades were developed

1970- improved. Pre cross-linked grades were developed.

1980- xanthogen disulfide grades were developed

1990- Newly developed M and XD grades combining low Temperature flexibility, heat resistance and dynamic properties as well as low fouling.

The major Manufacturers of Chloroprene rubber are

1.  Denka

2.  Neoprene

3.  Bayprene 

4.  Tosch 

CROSS REFERENCE OF POLYCHLOROPRENE GRADES

Lanxess	DuPont	Denki	TOSOH	Distugil
Baypren	Neoprene	Denka Chloroprene	Skyprene	Butachlor
General Purpose
110	WRT	S40V	B-5	MC-10
111
112	WX	S40/41	B-10	MC-20
210	W	M40/41	B-30	MC-30
211	WM-1	M-30/31	B-31	MC-31
230	WHV	M100/120	Y-31	MH-31
	WHV-100	M130H	Y-30	MH-30
	WD	DCR-30
Pre-crosslinked grades
214	WB	EM30/40	Y-20E	ME-20
115	TRT	ES40	E-20	DE102
215	TW	MT-40	E-33	DE302
	TW100	MT100		DE305
Sulfur modified grades
510	GW	DCR40		SC202
610	GRT	PS-40	R-10	SC-10
611	GRT-M1
	GNA	PM-40
Adhesive grades
320	AD 20	A90	G-40S
330	AD 30	A100	G-40T
340	AD40	A 120	G-40S3
321	AC-S	TA85	G41H	MA41H
331	AC-M	TA95	G41K	MA41K

CR grades 

CR grades are classified based on the following types
1.Mooney viscosity :
Mooney viscosity is determined by the molecular weight.
Low to high . i.e 20 to 140 ML4/100 C.
Low viscosity for ease of Processing, good flow properties.
High Viscosity for improved strength, High loading capability.

2. Crystallization rate
CR crystallization rate classified as fast, medium and slow or very slow.
Slow: Slow for Items requiring long term stability,like bridge,bearing pads, etc.
Medium- For general goods like hoses, moulded items etc.
Fast- Specially for Contact Adhesives.

3.Gel Content( Pre Crosslinked )- Reduced Nerve, Smoother and faster extrusion and calendering.

Polymerised CR consist of four types of isomers but their composition rates vary depending on the polymerization condition.When CR has many trans 1-4 structure it crystallizes easily.

Grades with high crystallization is used as rubber adhesives.

4. CR is classified into the following based on the modified grades are.

1.Mercaptan modified
2. Sulfur modified
3.Xanthane modified
4.Pre crosslinked modified.

       

1. Mercaptan Modified:

This group contains non pre cross-linked, sulfur free, soluble homo co polymer.

2. Sulfur Modified:
Sulfur modified type is unique because it's molecular weight can be easily reduced through mastication.It is obtained by co polymerization of chloroprene with small amount of sulfur followed by peptization of the resulting co polymer in the presence of tetra alkyl thiuram disulfide.

Characteristics of sulfur modified

* Mooney viscosity can be reduced through mixing.
* Greater tear strength
* Superior adhesion to fibres, steel cord etc.
* Generates less dynamic heat
* However the heat resistance is inferior to that of mercaptan modified.

3.Xanthane Modified:
 
The xanthane modified type produces vulcanized product possessing a high level of mechanical strength due to its active polymer molecule terminal.
It can also be designed using inexpensive blends based on high loading formulation because this also offers high anti vibration performance.

4.Pre crosslinked grades:

It is particularly suitable for extruded and calendared grades.

Selection of Compound Properties versus CR Grades
Desired Property Grades	Grades
Optimum processing	Grades of low viscosity, precrosslinked grades
Best mastication	S-grades
Best tackiness	S-grades; grades of low crystallization tendency
Best green strength	Medium fast crystallizing grades, high viscous grades
Highly extended compounds	Grades of high viscosity; XD-grades
Best extrudability	Precrosslinked grades

Compounding:

ZnO and MgO

• CR can be crosslink ed by metal oxides alone.

• Zinc oxide (ZnO) and magnesium oxide (MgO) are the most frequently used metal oxides;
•  lead oxides are used instead for optimal water,acid alkaline resistance.

• In the absence of zinc oxides the rheometer curve is rather flat. 
• Although the state of cure is increased, the crosslinking density remains low if zinc oxide is used alone.
• Best results are obtained with a combination of zinc oxide and magnesium oxide.
• There is a tendency to ‘‘marching modulus’’ characteristics if high levels of both metal oxides are used.
• The combination of 5 phr ZnO and 4 phr MgO is particularly favorable.

Red lead
For  improved water resistance, a lead oxide, usually 20 parts of red lead , may replace the magnesia /zinc oxide combination.
For health reasons, it should always be added as a dispersion,90% in EPDM. Owing to more limited reactivity with hydrogen chloride, stabilization is less efficient.

Carbon Black:

CB are preferred for processing and properties, Neoprene does not need high reinforcement,

•        HAF- For high abrasion Resistance ,MT- It is used for the soft compounds.
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•          The most highly reinforcing blacks N110 (SAF) or  (ISAF) can, under optimized mixing conditions, give the best tensile and tear strength values, dispersion difficulties in practice lead to N330 (HAF) or N326 (HAF-LS) being the finest particle carbons generally use.
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•            For most applications, N550 (FEF), N683 (APF), N660 (GPF), N772 or 774 (SRF) or N990 (MT) blacks, or blends, enable specification and service requirements to be met. N550, N683 or N660, alone or blended with N772 or N774 are preferred for extrusion or calendering Application.
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•            Where requirements permit, economical compounds may be prepared using high loadings of N772 orN774 or N660 blacks, with significant levels of plasticizer. 
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•          Alternatively, blends of N772 or N774 with mineral fillers such as china clay or whiting can be considered where compression set and physical property requirements are modest.

Fillers

Silica

•           Precipitated Silica- 10- 15 phr for improved tear strength.
•           Precipitated silica, preferably with up to 3 parts triethanolamine or other dispersing aid         if used at high  levels, gives the highest levels of tensile strength, elongation and tear          resistance.
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Calcined Clay

            Calcined clay- Electrical application, coloured compounds    Calcined clays are used for best          compression set and electrical properties.

             Calcium carbonate- Low cost

•            Talc- Coloured extrusion compounds.e most commonly used mineral fillers in Neoprene are precipitated silica, calcium silicate, china clay and whiting. 
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•          Hydrated alumina may be incorporated to raise ignition temperatures and limiting oxygen index values.
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•          Platy talc may be incorporated for good extrusion and electrical properties.

•           China clays may be hard or soft depending on the degree of reinforcement and loading required. 
•           Whiting finds limited use as a cheap non-reinforcing filler but it adversely affects weather    resistance. If used, a stearate coated precipitated grade is preferable.

Processing Aids:


 Processing aids include lubricants, tackifiers, and agents for controlling viscos­ity and nerve. Stearic acid, microcrystalline waxes, and low-molecular weight polyethylenes make good lubricants. 

          Hydrogenated rosin esters and coumarone­ indene resins are preferred as tackifiers. Viscosity modification may be achieved in either direction.

         Plasticizers:

•          Mineral Oil- Low cost
•          Naphthenic Process oil, compatible Upto 15 Phr
•          Aromatic oil Preferred for good building tack, inhibits crystallisation but limits low temperature flexibility and it will discolour and can stain on contact. Ester- relatively expensive 
•          Best low temperature flexibility but encourage  crystallization, reduce physical properties and ozone resistance, Light colored and do no stain .Volatility may be a problem, DOS is best for Low Tg
•           Vegetable Oils Such as rapeseed - good low temperature properties, excellent heat resistance.

•          The plasticizers and softeners most often used in neoprene are low-cost petroleum derivatives. Amounts ranging from 10 to 20% by weight of the filler load­ing are usually required for processing reasons alone.

• .         When the total amount of petroleum plasticizer fails to exceed 20 to 25 parts per 100 of neoprene, naphthenic oils may be used. These have the advantage over aromatic oils of not darkening light-colored vulcanizates or staining contacting surfaces. 
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•         When plasticizing oils are used in greater amounts in order to produce very soft vulcanizates or to accommodate the high amounts of filler used in low-cost compounds, aromatic oils are recommended to insure compatibility.
•            Petroleum plasticizers seldom improve the flexibility of a vulcanizate at                                low temperature.
•             Dioctyl sebacate is excellent for this purpose, although many other organic chemicals, mostly high-molecular-weight esters, are widely used.

Flame retarders

antimony trioxide

organic bromine compound

Processing:

• CR in general is available in the chip form.CR can be processed in mill using conventional or upside down technique.
• Add MgO at early stage and not to exceed dump temp of 130° C to prevent undesirable side effects.
• For high quality, low loaded compounds a two stage mixing in recommended with 1 day rest CR with S type shows mill sticking processors may assist in better mill release.
• Reversion not a problem so curing temp of 240°C are possible.
• Stearic acid 0.5-1 phr for CR to improve processing and reduce mill sticking.
• For CR with textile or metal bonding resorcinol type is used but because if scorching effect modified grades of resorcinol diacetate are recommended.
• Blowing agents used in other diene rubber are also suitable for CR.
• Compounding for special requirement.

Physical Properties:

• Polychloroprene vulcanizates possess good physical strength, and with optimum formulations, the level is comparable to that of NR, SBR, or NBR.

• Tear resistance of CR vulcanizates is better than that of SBR. Tear propagation resistance of CR vulcanizates containing active silica may be greater than that of those with natural rubber. 

•  The compression set of CR is low over a wide range of temperatures from -10 degree C to 145 degree C.
• For CR, testing is commonly run at -10 degree C, the temperature at which optimum crystallization occurs. It is possible to improve the low-temperature compression set to less than 50% at -30 degree C by using the most crystallization resistant CR 
• The abrasion resistance of CR is comparable to that of NBR 

Abrasion resistance:

To improve the Abrasion resistance N330 or 326 40 parts can be added N326 particularly useful where abrasion resistance is required.

H      High Strength at Elevated Temperatures

•         Precipitated silica up to 40 parts, preferably with up to 3 parts triethanolamine or other surface-active dispersing aid, is particularly effective in retaining vulcanizate physical properties at temperatures to 200°C short term.

Tear Resistance

• Sulfur modified grades are good than other grades. They possess excellent flex fatigue resistance with usually adequate compression set resistance. 

• Among fillers, precipitated silica with a dispersing aid is the best but other minerals such as silicates and hard clays may also give better tear values than most carbon blacks, at the expense of  poorer compression set resistance.

•  N326 (HAF-LS) carbon black can give a good balance of tear and set properties provided that good dispersion is achieved,oil addition should be avoided during incorporation of the black. 

• Resinous plasticizers such as coumarones or alkyl aromatic, at 5 parts also help achieve optimum tear strength. Natural rubber, 10–20 parts, may also assist but inevitably diminishes oil and ozone resistance.

Electrical Properties 

•  Neoprene is not normally considered a primary insulating material. To optimize its capabilities, mineral fillers should be specified for their higher insulation resistance and dielectric strength as compared with carbon blacks.

•     Platy talcs such as Mistron®Vapor are recommended for dielectric strength. 
•     Ester plasticizers should be avoided. 

•     Up to 15 parts naphthenic oil may be incorporated but a hydrocarbon resin, such as Kenflex ®A-1, will optimize insulation resistance.

•       Where antistatic properties are essential, incorporation of conductive furnace blacks such as    N283 (CF) or N472 (XCF) will achieve this, as in other elastomers

Food Contact

• In order to chose the material for food grade the required safety data sheet and technical data sheet  of each base polymer can be referred.

•   ETU is not an acceptable accelerator.Alternatives to ETU are chosen. Mixland®+ SD 75 GA F250 in combination with Mixland®+ DPG 80 GA F140  is one of the alternative for Na free solution from arkema group.

          Flame resistance

•        The inherent self-extinguishing characteristics of all Neoprene grades may be enhanced or diminished by compounding.

•          Chlorinated paraffins varying between 40 and 70% combined chlorine contents, solid or liquid, may be used both to plasticize and to increase the available chlorine level.Blends of solid and liquid chlorinated paraffins also reduce sticking tendencies.  

•           Hydrated alumina enhances self-extinguishing characteristics and raises auto-ignition temperatures. It may be used in combination with carbon blacks to achieve tensile requirements. China clays and calcium silicate are also used but do not have the specific effects of hydrated alumina. 
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•          Other additives to enhance self-extinguishing include antimony trioxide, alone or preferably as a synergistic 3:1 combination with decabromo biphenyl ether

•           Magnesium hydroxide finds use as a smoke suppressant. 

•           Hydrocarbon-based plasticizers and process aids should be avoided or severely restricted since they support combustion.

Building Tack

• Aromatic plasticizers give more tack than naphthenicor ester types.
•  Other tack promoters are coumaroneindene resins, especially liquid types, wood rosin and phenolic resins such as Koresin. 
• Aromatic oils are more prone to cause troublesome roll sticking than other types.
•  As noted under Processing Aids, 3–5 parts high-cis 1,4-polybutadiene can alleviate problems of excessive roll sticking. 
• To maintain building tack no dusting agents should be applied to sheeted stocks. Batch-off liners should be nonstick

     Adhesion:

•         Combination of HAF with 10 phr precipitated silica improve the bond strength  Plasticizer - Aromatic oil.
•         For direct bonding to non ferrous metals such as brass or zinc may be accomplished without  using primer  by 1.5 phr of sulphur . In these case ETU derivative should be avoided.

    Compression Set resistance:

•        For recovery from compression at low temperature the minimum level of water plasticizer such         as 10 parts DOS should be used.

    Crystallization resistance:

•         Inclusion of 1 phr sulphur will retard vulcanization crystallization at he expense of heat aging      and compression Set resistance.

    High strength at elevated temperature:

•        Precipitated silica Upto 40 parts preferably with 3 parts triethanolamine or other surface active   dispersing acid is effective.  

   
Vibration Dampening:

•         High-mechanical damping is diametrically opposite to the requirements for high resilience. A typical application is machinery mountings in a hot and/or oily environment.

•          Appropriate compounds are usually highly filled with soft black, china clay and aromatic oil hence high Mooney Neoprene WHV or WHV-100 or M 100, Y-31 or MH-31  are preferred. 
•            ETU acceleration is required for practical cure times and minimum creep in service.

Resistan ce to Fun gi and Bac teria

                

R         Rubber  articles in contact with soil for longer periods of time are liable to attack by soil bacteria and fungi . This can lead to underground cables being destroyed.In contrast to the majority of other rubber types , CR shows a surprisingly higher level of resistance to these microorganisms. This resistance can b e further enhanced  the use of fungicides such as Vancide 51Z and a fungus -resistant plasticizer polyether-[di (buto xy-et hoxy-ethyl) formal].

 Application:

Vibration damping:

• High-mechanical damping is diametrically opposite to the requirements for high resilience. 
• A typicalapplication is machinery mountings in a hot and/or oily environment. 
• Appropriate compounds are usually highly filled with soft black, china clay and aromatic oil hence high Mooney Neoprene are indicated. 
• ETU acceleration is required for practical cure times and minimum creepin service. 

Hoses:

• CR is the classical elastomer for hose covers. Industrial hydraulic hoses, either medium- or high-pressure types, currently contain CR covers.
•  For cost reasons, blending with SBR is practiced. CR covers are also used where hoses resistant to oil and ozone are required. tubes and general tubing for the automotive industry.Other applications of importance are suction and discharge hose covers and tubes and general tubing for the automotive industry.

Molded Goods

•  Bellows and seals for various applications, of which axle boots are a typical example  are made from CR.  The compound is designed to have excellent low temperature, flex, ozone,  and weather resistance.
• CR has been used for many years as the elastomer of choice for bearings in  machinery and bridges.

Belting

•      CR is the dominant elastomer for power trans mission and timing belting.
•      Other uses include various industrial belts.

•     The compound is designed for excellent flex resistance.
•     The polyester fiber is used for good dynamic compression resistance.
•      Mining conveyor belts are based on CR where stringent flame retardance requirements               must    be fulfilled .
•     Flame retardant mineral fillers used in combination with a chlorinated wax are                            recommended  along with a Silica filler for abrasion and tear resistance.

Extrusion 

• Automotive  and building profiles in the hardness range of 50 Shore A to 90 Shore A and sponge pro files have been in use for many years.
•  In the construction industry, some CR has been replaced by EPDM for cost reason s; however, CR is still the prefer red polymer if flame retardance and some oil resistance are required.

Wire and Cable

CR is the polymer of choice for cable jacket s in heavy duty applications like transport,mining, welding , and others.

Miscellaneous

• Some other applications are rollers for the printing and textile industry, coated fabrics, membranes, air bags, tank linings, closed cell sponge surf, and diving suits.