Developments in compounding.

Developments in compounding

The problem of estimating the future needs when related to compounding depends on the compounder's relationship to his working environment.

Perhaps this is best illustrated by the diagram described by B.S. Garvey, Jr. in the first edition (1959) of "Rubber Technology" (figure 1).

However, it is obvious from the flow diagram that only a large organization would have all of the departments as shown above. Smaller companies in many instances do not have research groups to back up product development and production.

In these instances, the chief compounder (or only compounder) has to depend on the information received from material manufacturers and suppliers. But the diagram does reflect the ideal situation regarding compounding in the 1980s and in future years even though the idea was written over 30 years ago. The compounder's function is best described in the 1978 Vanderbilt Rubber Handbook as follows:

"He must be able to select the proper elastomers and additives available to meet the conditions of the finished product. This requires a thorough understanding of the following:

* Properties of the elastomers available.

* Vulcanization or curing systems to give the potential properties needed.

* Modifying materials which give the required physical properties and aging resistance.

* Compounds must be able to process properly depending on processing equipment.

* Commercial compound design, and

* How to test and evaluate raw materials and finished products."

From this standpoint, the compounder must be well aware of the changes being made in the production and availability of elastomers and the ingredients used in rubber manufacture. This will be the basis for the following discussion in this article.

Availability of ingredients

A survey was made using the "Blue Book: Materials, compounding ingredients, machinery and services for rubber" for three periods, 1968, 1980 and 1989 to illustrate the changes occurring in the industry over this period of time in order to show trends that occur due to OSHA requirements, buy-outs and mergers.

Naturally, this source has changed its contents over this time period, however, the trends are still a good indication of how the industry has changed or may change during the next decade or two. The number of suppliers has increased over the past 10 years, as indicated in table 1.

Table : Table 1 - Blue Book suppliers

1968 1980 1989

Material and ingredient

  suppliers                       Not listed      288       344
Custom mixing                     Not listed       23        57

Machinery and equipment

suppliers (with products) Not listed 275 332

From this information, it is obvious that there is still a large increase in the number of suppliers over this period, and furthermore, the growth in the use of custom mixers has increased 230%, indicating that this is a cheaper way of processing or that the custom mixer is supplying a quality product to the smaller producer of molded rubber products, thus eliminating his need for expensive mixing and testing equipment.

Elastomers

The International Institute of Synthetic Rubber Producers (IISRP) indicates that total rubber consumption will increase 11% from 1988 to 1993 (10.9 to 12.1 million tons). How this increase will affect production and sales of each individual elastomer remains to be seen.

Table 2 shows the number of listings for each elastomer for these periods (Blue Book data).

Table : Table 2 - number of listings

Elastomer 1968 1980 1989

Natural rubber

  Standard international grades          31        35        35
  TSR (SMR types)                         3         9         9
  Specially prepared grades               4         6         6
  Modified                                2         4         4
                              Total      40        54        54

Synthetic rubbers

  Acrylics                               13        16        16
  Chloronated polyethylene                0         4        14
  Chorosulfonated polyethylene            4         7         6
  Epichlorohydrin                         2         5         8
  Ethylene-acrylic                        1         1         7
  EPM                                     1         7        10
  EPDM                                   11        50       101
  Fluorocarbons                          10        28        75
  Butyl                                  28        16        22
  Nitrile                               106       166       229
  Butadiene                              25        23        47
  Chloroprene                            25        43        67
  Polyisoprene                           13         5         8
  Polynorbornene                          0         0         5
  Polysulfides                           10         8        15
  Silicones                              71        55       104

Synthetic rubbers

SBRs

    Solution and block                   NL        31        35
    1000 (Hot)                           39        25        18
    1500 (Cold)                          52        28        18
    1600                                 32        17         9
    1700                                 67        22        14
    1800                                 74        26        29
    1900                                 35        11         9
    Cold latex                           49        16         7
    Hot latex                            88        34        25
  Styrene-isoprene                        0         1         6
  Thermoplastic elastomers                8        10        66
  Transoctenamer                          0         0         1
  Urethanes                              42        84        90
  Vinyl acetate/ethylene                  0         2        10
  S-B resins                             11         4        11
  Reclaims and regrinds                  33        33        33
Reprocessed synthetic rubber              0         7        35

There has been no change in the number of natural rubber grades over the last 10 years, however, production is estimated to increase 9.8% from 1988 to 1993. Over the last 20 year period (1968-1989), only small changes in listings occurred for the acrylics (13 to 16), chlorosulfonated polyethylene (4 to 6), polysulfides (10 to 15) and little or no change for S-B resins.

Large increases occurred for the ethylene-acrylics (1 to 7), EPDMs (11 to 101), fluorocarbons (10 to 75), nitriles 106 to 229), butadienes (25 to 47), chloroprenes (25 to 67), silicones (71 to 104), and especially the thermoplastic elastomers (8 to 66) and the urethanes (42 to 90).

The large growth in EPDMs is mainly due to its use in single ply roofing material. EPDM is now second in usage after the conventional roofing materials, replacing Hypalon as the most popular elastomer for this usage.

Listing decreases occurred for butyl (28 to 22), polyisoprene (13 to 8), and especially for the various types of SBR (436 to 164). This decrease for SBR shows that the number of producers is decreasing, but predicted SBR usage will increase 8.8% from 1988 to 1993, as predicted by the IISRP. It must be noted that the number of listings in many cases either indicates a reduction in the number of producers or a decrease in the grades that are available. For example, the number of black-oil masterbatches and oil masterbatches has decreased probably due to a decrease in the types of oil and blacks available.

Table 3 illustrates the rapid growth in the number of producers of thermoplastic elastomers since the production of the Solprenes in 1963 and the Kratons in 1964.

Table : Table 3 - thermoplastic elastomers

                              Number of manufacturers
Product type                  1975      1985      1987
  Polyurethane TPE               3         8        10
  Styrene-diene blocks           2         3         6
  Polyolefin blends              1         7        18
  Styrene-EB blocks              1         1         1
  Copolyester-ester              2         4         5
  PVC-TPE                        0         2         3
  Polyamides                     0         2         3
  Others                         1         1         4
                        Total   10        28        50

Elastomer latices

Table 4 shows the listing for the various elastomeric latices over the same time period (1968-1989). For each elastomeric latex type there was a decline in the total number of listings with the disappearance of fluoro, isoprene-acrylonitrile, butadiene, butyl and isoprene latices. However, these are probably available on a special order basis. Both nitrile and SBR latices declined in their listings (45 to 16) and (25 to 13), respectively.

Table : Table 4 - latex listings

Elastomeric latices                     1968      1980      1989
  Acrylics                                19        14        22
  Fluoro                                   0         2         0
  Isoprene-acrylonitrile                   0         1         0
  Natural rubber                          12        12        14
  Nitrile                                 45        15        16
  Chloroprene                             13        14        13
  Styrene-butadiene                       25        50        13
  Vinyl pyridine                           3         7         5
  Butadiene                                1         0         0
  Butyl                                    1         0         0
  Isoprene                                 2         0         0

Elastomeric latices

In all cases there was a decline in the total listings for each latex, with the complete disappearance of fluoro, isoprene-acrylonitrile, butadiene, butyl and isoprene latices. Apparently there was insufficient demand for these products.

One of the greatest failures has been the inability of anyone to produce a synthetic polyisoprene latex with all the characteristics of natural rubber latex. The only latex listed in 1969, produced by Shell, never had all the properties desired in a latex of this type.

Although SBR listings have decreased from 25 to 13, the predicted usage of these latices will increase 8.8% from 1988 to 1993 (IISPR data).

Compounding ingredients

Table 5 shows the listings for some of the major ingredients used in elastomeric compounds for both dry rubber and latex materials. It should be noted that many of the listings for individual materials are high as there are so many forms available for the same ingredient, ie., powdered, rod-form, pastes, dispersions, elastomeric blends and micro-encapsolates, etc.

Table : Table 5 - compounding ingredients

Rubber compounding ingredients          1968      1980      1989
  Accelerators                           277       437       718
  Activators                             200       226       384
  Retarders                               25        45        47
  Vulcanization agents                   140       254       433
  Antidegradants and inhibitors          356       341       476
  Chemical and heat stabilizers          135        72        62
  Homogenizers                             0         4        13
  Peptizers                               31        14        25

Processing aids and dispersing

    agents                                87       126       205
  Tackifiers                             122       166       167
  Platicizers and softeners              741       570       601
  Short fiber reinforcing materials        0         0         5
  Carbon blacks                          117       158       131
  Other black materials                    4        11        22
  Non-blacks                             362       320       423

Adhesive, bonding and sealing

    agents                                72       147       186
  Blowing agents and blow promoters       58        63        76

Dusting, dipping and washing

    materials                             64       103       129
  Finishes                                 0        51        62
  Lubricants (molds and internal)        184       209       237
  Odorants and non-staining agents        54        16        13

Latex compounding materials

  Anti-blocking agents                     6         7        10
  Anti-foaming agents                     36        54        51
  Anti-webbing agents                      3         2         5
  Coagulants                              11        15        40
  Creaming agents                          1         3         1
  Dispersing agents                       42        39        40
  Gelling agents                          11        10        14
  Preservatives                            4         9         5
  Stabilizers and emulsifiers             93        55         8

Thickening, viscosity stabilizers 

    and reducers                          19        20        26
  Wetting agents                           7        21        10

However, predicted production will increase from 382 to 400 million pounds from 1988 to 1989, according to a Chemical and Engineering News April 17, 1989 story. All U.S. producers ([is greater than] 20) are running at full or near capacity for the manufacture of these items. The C&E News article indicates that there are over 50 suppliers in the U.S. alone with some of the manufacturing in other countries. This figure does not include fillers, colorants, plasticizers and softeners. It is interesting to note that there is a trend toward supplying many of the compounding ingredients as dispersions or elastomeric blends. Some examples are shown in table 6.

Table : Table 6 - blends and dispersions

                                        1968      1980      1989
                                            Listings available
Accelerators   Dispersions                35        56        67
               Elastomers blends          39       134       183
Activators     Dispersions                 8        42        38
               Elastomer blends           11        57        69
Vulcanization  Dispersions                16        40        39
  agents       Elastomer blends           13        79        89
Antidegradants Dispersions                50        15        13
  and inhibitors Elastomer blends          0         4        12

Many of the dispersions are for latex use and this is especially noticeable with antidegredants and inhibitors since a large decrease has occurred since 1968. The increase in elastomeric ingredient blends reflects both the storage stability and the ease of measuring and using these materials.

The decrease in carbon black listing from 1980 to 1989 shows the effect of eliminating the manufacture of channel blacks and several grades of both thermal and furnace blacks.

In the third edition of "Rubber Technology," J.T. Byers predicts that perhaps 11 grades of carbon black have a "questionable future" and may be dropped due to decreasing use and some of the structure levels may be discontinued from manufacture.

The Blue Book in 1980 listed 40 grades as compared to 32 in the 1989 edition. Apparently the trend is continuing. The compounder must be aware of these changes and be willing to make substitutions when necessary before supplies are not available. He needs the aid of both the producer and supplier to prevent serious problems in his production of vulcanized goods. This is also important when considering all of the compounding ingredients that he uses.

Summary

The usage and supply of the basic materials utilized by the compounder seem to be on an even keel since many of the items still available may function to produce a satisfactory vulcanizate, however, he has to be prepared to replace items as they are discontinued or eliminated by OSHA's requirements.

Fortunately, there are newer modifications of elastomers being developed (hydrogenated nitrile and epoxidized natural rubber are two examples) which aid the compounder in the selection of basic elastomers. In the past two decades, instrumentation has been computerized to the point where mixing, processing, vulcanization and testing data is stored and can be recalled when needed.

This type of instrumentation, curemeters for example, has greatly aided the compounder in developing compounds and aids in maintaining quality control of production items, as the search for uniformity will continue.