PLTC NR compound for a high duty offshore oil-production engineering application.

Tension leg oil field platforms are a relatively recent concept for oil rigs in that they are made to float (by means of inflatable pontoons) rather than stand on the sea-bed, so that their legs provide mobile links to a firm location on the sea-bed. (A crude analogy for these legs is the guy ropes used on tents when camping.) The floating platform is therefore subject to wind, tide and wave movements, etc., so that linkage points are necessarily made through beatings. The chosen design is a semi-spherical rubber to metal laminated beating, called a flexelement. Elsewhere in the platform, "flexjoints" are used, of similar construction but allowing flow of production fluid along their central axes. Both components must have sufficient stiffness and adequate rubber to metal bonding levels for engineering requirements of service (ref. 1), while allowing for the inevitable motions occurring offshore.

To aid the design of these critical components, a manufacturer has been one of a team of sponsors of a project in which novel processable low temperature curing (PLTC) natural rubber (NR) elastomers have been produced. The designated low temperature is 70 [degrees] C which, besides giving considerable energy savings during curing (a main thrust for this project), meant that reduced shrinkage from lower manufacturing temperatures will improve dimensional features throughout the finished flexelements and flexjoints.

Approach

During the initial stages of the curing process, flexelements are molded at 30 [degrees] C below their eventual curing temperature, which is in the normal range applying to NR. Following the same philosophy, as the target curing temperature for this project is 70 [degrees] C, then consequently the molding temperature should be 40 [degrees] C. A currently-used NR compound was supplied to be a benchmark control throughout the development, so that performances of experimental NR PLTC compounds could then be compared at their low processing and curing temperatures with those of the control at its normal processing/cure temperatures.

Clearly, to bring about molding at 40 [degrees] C, the compound needs to be more pliant than normal. For this, the essential constituent in these processable low temperature curing natural rubber formulations is liquid polybutenes (PB) of a form to induce compound moldability at 40 [degrees] C. The other class of essential ingredient for PLTCs is a group of particular ultra-fast accelerators to bring about the vulcanization at 70 [degrees] C. Hence the approach adopted was to achieve the correct degree of moldability at 40 [degrees] C and then develop the curing system. The first stage involved finding the best balance of base rubber and PB to satisfy all requirements. The PB chosen, with a molecular weight of 950, is termed PB 950.

Processability

In order to preclude any effects of scorch on the measured data, the flow rate analyses were performed on masterbatches. Flow rates were measured on a simple plunger capillary rheometer. It consists of a steel cylinder that contains the rubber, firmly screwed into one of a series of steel circular base plates, to make a pot. Each plate contains a hole of a specific bore diameter and length, the hole being drilled normally through its center. A band heater was fitted closely around the pot, with suitable temperature feedback control and another thermocouple to record actual temperature of the test compound when in place. A steel plunger was inserted into the pot after the test compound, and a desired constant pressure applied compressively to the rubber compound over a period of time by placing the equipment in a universal tester. On achieving equilibrium at test temperature, the rubber that consequently extrudes through the bore hole was cut off at intervals of one minute, and weighed, to give a flow rate for the particular hole dimensions being used. By increasing the pressure in desired increments, the measured flow rate of the rubber increased accordingly.

A target flow rate was first set by examining the control compound. Using various bore hole dimensions, the flow rates of the control rubber were investigated at a temperature 30 [degrees] C below its normal curing temperature - a temperature typically applying for normal NR compounds. From these results, it was decided that a 3 mm diameter and 20 mm length bore hole base plate gave rise to the best balance of reproducibility and sensitivity for making the necessary comparative flow rate tests. More preliminary testing was performed, now to assess the effects of increasing molding pressure. As molding pressure was increased, a non-linear form of increase in flow rate of control compound through this optimum hole at its normal high molding temperature was observed. These measurements were merely to lead to the optimum conditions for performing the flow rate analysis of PLTCs; it transpired that an applied force of 2 kN (giving a pressure of 2.83 MPa - 410 psi - with the plunger used) was the best to use for the ensuing PLTC development.

For the PLTCs, the flow rate testing was carded out at the target molding temperature of 40 [degrees] C as discussed previously. In order to simulate production-mixing conditions, a series of masterbatch compound samples was worked on a two-roll mill at ambient temperature for twenty minutes prior to the test. Only one of the masterbatches at 40 [degrees] C satisfied the viscosity requirement of the control compound at its higher molding temperature with a slightly faster flow rate (lower viscosity). The formulation for this masterbatch is shown in table 1.

PLTC shelf life

The shelf life associated with pre-cure storage of the compound is a very important factor when developing low temperature curing compounds. For producing flexelements, etc., due to summer ambient temperatures in Texas being up to 40 [degrees] C, it was agreed that a shelf life for the PLTCs should be either five days at 40 [degrees] C or 50 days at 10 [degrees] C (for compound storage in a refrigerator). By defining shelf life in the same way as curemeter scorch ([t.sub.2]), a manufacturer's target line could be shown as an Arrhenius-type plot, included in figure 1. Also shown in the figure is the letter X which signifies in the same manner a period of two weeks at 23 [degrees] C, which is deemed a suitable period of time for a compound in a controlled comfortable environment to be left standing in a factory before being cured. Actual curemeter test data could then be added to the same figure for comparison purposes.

PLTC formulations

For the majority of the compounds, the curatives were added to the masterbatch on a cool mill in order to minimize scorch aspects. However, there were a few compounds where this procedure was not employed and a note is made to that effect at the time. Ultra fast accelerators ZDBCX (amine activated zinc dibutyl dithiocarbamate) and ZIX (zinc isopropyl xanthate) and established accelerator MBTS (originally intended here to act as an inhibitor) were initially investigated as an EV-type combination. This gave EV compound with a cure time 095 at 70 [degrees] C) of 88 minutes but a shelf life ([t.sub.2] at 40 [degrees] C) of only 100 minutes (Compound A in table 2). Based upon the result from this formulation, a series of further compounds was investigated (table 2) in which: The MBTS level was increased; and the MBTS was respectively substituted by Inhibitor E (N-phenyl-N(trichloromethyl sulfonyl)-benzene sulfonamide and Inhibitor G (N-cyclohexyl-thiophthalimide [CTP]). The curatives were normally incorporated at fairly low temperatures, below the melting points of the inhibitors. Thus, it was deemed worthwhile to see whether an improvement in cure time and scorch-delay characteristics would be achieved by the act of melting one of the new inhibitors during mixing, hopefully to improve the quality of its dispersion. Inhibitor E was first mill-mixed into Masterbatch A at 120 [degrees] C, which is 10 [degrees] C above its melting point (Compound D). The mix was then cooled down to room temperature and the remaining curatives added. All the compounds had curometry tests conducted at 40 [degrees] C, 70 [degrees] C and 100 [degrees] C. Table 2 shows the [t.sub.2] data.

The curometry results for Compounds B to E were compared with those of Compound A:

* Compound B - The 50% increase in the MBTS level not only reduced the cure time ([t.sub.95] at 70 [degrees] C) by over 20%, but also the shelf life by almost 10%. It appears that the MBTS has no inhibiting characteristics at the temperatures of interest here (although such characteristics were indicated by the [t.sub.2] values at the higher temperatures).

* Compound C - The MBTS was substituted by Inhibitor E, but the relevant changes in both cure time and shelf life were insignificantly different from those seen for Compound B.

* Compound D - This has the same formulation as Compound C, but Inhibitor E was melted, which resulted in the shelf life being greatly increased to 219 minutes; furthermore, the cure time was reduced to 62 minutes.

* Compound E - Inhibitor G was used instead of MBTS and produced a large reduction in cure time to 54 minutes, with the shelf life also showing an increase to 115 minutes.

Compound D (melted Inhibitor E) has the best combination of cure time and shelf life. However, while its Arrhenius plot is much closer to the target line than that for Compound A, it is still a significant distance away (figure 1).

[FIGURE 1 OMITTED]

Further investigations were carded out using greatly increased loadings of melted inhibitors E and G (Compounds F and G, respectively, in table 3.

Great improvements in shelf lives are seen for both Compounds F and G, especially for the former compound (as shown in figure 1), but in both cases the cure times associated with marching moduli are unacceptably long.

The EV development was showing great steps towards very long shelf lives, but unfortunately the cure times were being adversely affected. Thus, a fresh approach was adopted with the use of a higher sulfur content curative system (Compound H [table 4], which also includes relevant curemeter data, including torque data).

While the cure time at 70 [degrees] C is almost twice that for Com pound D, it is still at an acceptable level and with a shelf life (40 [degrees] C [t.sub.2] scorch) over twice as good as that for Compound D, as also indicated in figure 1. Hence, Compounds D and H possess recipes of two different types, both displaying promise. One (Compound H) accentuates shelf life features; although not to the ideal manufacturer's target line level, it was considered that the life attained led to a workable manufacturing scenario. On the other hand, Compound D would produce fully-cured material in a reasonable cure time at 70 [degrees] C, providing a rapid through-put of uncured compound was ensured.

Mechanical testing

Mechanical testing was restricted to one compound each from the EV and high-sulfur approaches - Compounds B and H, and the results were compared with the control data. It was not expedient at the appropriate time to test Compound D (preferred for the cure-linked reasons given above as the EV representative), but generally the project has not indicated differences in mechanical property levels for recipes of a similar type cured to [t.sub.95]. For the PLTCs, rubber-to-steel bond strengths after 70 [degrees] C curing were determined for B only, and compressive creep, fatigue and fluid absorption conducted for just Compound H.

Compound B

To see how a PLTC compound is affected by various curing/aging procedures, mechanical properties were measured before and after the following regimen was carded out for Compound B:

* Cure to [t.sub.95] at 70 [degrees] C (unaged);

* cure to twice the [t.sub.95] value at 70 [degrees] C (overcured);

* cure to [t.sub.95] and then age in an oven for 16 hours at 70 [degrees] C (aerobic postcure);

* cure in mold under pressure for 16 hours at 70 [degrees] C after [t.sub.95] (anaerobic postcure);

* cure to [t.sub.95] and aging in oven for seven days at 70 [degrees] C (aerobic aged);

* cure to [t.sub.95], oven-age still in mold (clamped) for seven days at 70 [degrees] C (anaerobic aged).

Procedures akin to these six were also carried out on the control compound, but at its normal high curing temperature. Both Compound B and the control compound were compression-molded to optimum values, results after mechanical testing being shown in table 5 for Compound B and table 6 for the control. For overcured and aged samples, values in brackets represent the change that has occurred from the unaged results. Some weight changes were also obtained to check on the PB volatility. For the compounds that had received anaerobic overcuring or aging, the change in weight could not be ascertained as specimens remained in the mold during aging, and flash became a complicating factor.

* Unaged - Comparing Compound B with the control compound, hardness, tensile strength and modulus are less, elongation at break value is roughly the same and the trouser tear is better. It was agreed that, generally, the mechanical values of Compound B would be acceptable for the application.

* Overcured - Compared with the unaged values, there is a large reduction in some of the mechanical properties of the compounds. When cured to twice [t.sub.95] (overcure), the control's trouser tear strength reduces by 74%, while Compound B decreases by 65%. The tensile values (tensile strength and elongation at break) reduce by about 25% for the control and about 5% for Compound B; modulus change is less for B. Overall, Compound B, when compared to the control, performs better after being cured to twice [t.sub.95].

* Aerobic postcure - The control compound has reductions in tensile values of about 70% and in trouser tear of 78%. Compared to the control, Compound B has slightly lower trouser tear reduction (64%) and much smaller reductions in tensile values, ca 30%.

* Anaerobic postcure - The trouser tear values for both compounds are all reduced by about 75%, while the reduction for the tensile data is of the order of 50% for the control and about 25% for Compound B. Thus, as with overcuing, Compound B generally performs better than the control after being postcured (aerobically or anaerobically).

* Aerobic aged and anaerobic aged - Some fluctuations occurred with data obtained after seven day aging. The reduction in trouser tear strengths for the control are of the order of 62%, and for Compound B, 87%. For the tensile values, the reduction in values for the control is about 48%, while for the Compound B the reduction is of the order of 70%. Compound B does not age aerobically or anaerobically as well as the control, except for modulus and hardness after the anaerobic treatment.

The aerobic overcure for the control compound causes more weight loss than that of Compound B when it undergoes aerobic postcure and aging. For both compounds, the maximum weight loss is only 2%. As the weight loss for the PLTC compound is in fact less than that for the control compound, then any loss of polybutene must be minimal.

Rubber to metal bonding

For flexelements and flexjoints, their successful deployment requires good levels of adhesion between the steel laminates and intervening rubber layers. This requirement is readily attained for normal NR systems, but it was deemed necessary to check a number of proprietary bonding systems to determine if they were still active at 70 [degrees] C curing temperatures. Preliminary work using peel adhesion tests has been performed on PLTC Compound B, again comparing with the control.

Peel adhesion testing was used to assess the rubber to steel bonding levels. Steel strips were grit-blasted (60/80 alumina) and solvent-treated, coated with adhesive layers (with suitable drying periods between and after coatings), and placed on the base of a plunger mold. 25 mm strips of masking tape were positioned on the ends of the strips, a PLTC compound layer ca 4 mm thick was placed to cover all of the strips, the plunger lid added, and molding/curing to [t.sub.95] at 70 [degrees] C performed. The masking tape ensured formation of tabs for subsequent gripping in the test machine jaws. The control compound was cured to [t.sub.95] at its normal high curing temperature. For testing, a strip was located horizontally in the lower test machine jaws, and 90 [degrees] peeling performed by pulling the rubber tab vertically upwards. Peel adhesion was taken as the mean of the most representative peaks on the test trace divided by the test piece width.

For Compound B, the Chemlok 289/290 primer/cover system was first assessed, to give an average strength value of 5.4 N/mm - a moderate value only, with no associated cohesive failure. Hence, a tacky tiecoat was added. With the Chemlok 289/290/286 combination, an average strength of 9.85 N/mm was obtained. The second system gave good bonding; the tested surfaces showed signs of fine-scale cohesive failure over the whole bonded area.

For the control compound, the 289/290/286 system gave an average strength value of 15.5 N/mm, while both the Chemlok 205/234B and 289/234B systems gave average strengths of 11.8 N/mm - both good values - as would be expected. See table 7 for additional background.

Compound H

The mechanical properties of Compound H cured to its [t.sub.95] value of four hours are shown in table 8, as are those of the control compound cured both to its [t.sub.95] value (15 minutes) and for four hours at its normal high curing temperature.

The mechanical properties of the 15 minute cure control compound are a little higher than those obtained previously at the same conditions (table 4). Compound H has a similar tensile strength, higher elongation at break and also much the greater trouser tear strength, but is slightly softer. These are good values, differences probably reflecting the lower hardness.

Creep testing in compression

Creep is a time-dependent increase in deformation under constant load. As it applies directly in a compressive mode to flexelement service, the decision was made to perform three compression creep tests on PLTC Compound H under realistic but simplified conditions to check long term performance. It is well-established that, at constant temperature, the rate of creep (and of its related time-dependent property stress relaxation) depends on the logarithm of time, providing that no chemical attack occurs. Hence, tests were performed at 23 [degrees] C to minimize any chemical effects, and to be within 10 or 20 [degrees] C of typical service temperatures. Each PLTC sample molded under compression was a rubber cylinder (diameter 30 mm, depth 13 mm) cured to optimum at 70 [degrees] C and Chemlok-bonded to steel discs at top and bottom; this depth equated to a typical layer thickness for a flexelement.

A compressive strain of 13% was applied and maintained, and creep tests then performed on three replicates using a Zwick universal tester. The deformations versus log time result are plotted in figure 2 and show good reproducibility. In each case, the load was applied in less than 20 seconds, and good linear plots of the subsequent creep stage were obtained. According to these, after 90 years (i.e., a working life of 30 years multiplied by a safety factor of three, as usual for offshore engineers), the extra deformation due to creep would be ca 0.75 mm, or less than 5.75% based on the original thickness of 13 mm. Of course, these values would need to be scaled up according to the actual strains (at 20% compressive strain, the creep after 90 years of 5.75% would be estimated to have increased to ca 9%), and the number of layers in the flexelement. However, clearly the ambient temperature creep level of this PLTC for such a long time is not excessive.

[FIGURE 2 OMITTED]

Fatigue life

The basic form of assessing fatigue performance of rubbers uses a fracture mechanics approach. The established procedure is to develop log/log plots of crack growth rate (dc/dn, in mm.) versus tearing energy (T, in kJ/[m.sup.2]) using results from dynamic testing in which samples are repeatedly stretched and relaxed. Simple geometries are used for the samples, with associated equations for calculating tearing energies.

To prepare for testing, a crack is introduced half way along one of the sides to be stretched. The initial crack must be uniform and sharp (preferably from a new scalpel blade), being ca 20 mm long for pure shear samples and 0.5-1 mm for the extension ones.

The fatigue performance across the main crack growth stage of PLTC Compound H has been compared with those of the control compound at two cures, and found to be very similar (table 9), all data measured for the three samples fitting on the same straight line (figure 3). This is encouraging regarding the performance of the PLTC. Moreover, as the tear strength of PLTC Compound H was much higher than those of the control at optimum (short cure) and long (four hour, representing surface-cure conditions) times, the catastrophic regions should be further displaced for the PLTC, as indicated by the arrows at the top of figure 3.

[FIGURE 3 OMITTED]

Sea water exposures

In order to give some indication of the long term effect of exposing Compound H to sea water, greatly accelerated conditions were used. Two samples underwent a 49 day exposure in boiling sea water. Both samples were discs of 30 mm diameter and 8 mm length that had been cured for four hours at 70 [degrees] C. In order to represent the geometry of the service situation, i.e., of a flexelement, one of the samples had metal discs bonded to the top and bottom surfaces during curing (termed shielded). Both samples were fully immersed in the boiling sea water, and weighed periodically. The results for both the shielded and the free samples are plotted in figure 4.

[FIGURE 4 OMITTED]

A sea water extraction test carried out on the free sample of Compound H resulted in a weight loss of about 2% (assessed by weighing after post-test drying). Taking this into account, the final (49 day) absorbed value of just over 1% shown in figure 4 for the free compound should really be ca 3%, although still rising slowly. The shielded compound has contact with the sea water restricted to the peripheral surface, which results in the sea water having very little effect on any weight change during the time of this test, as evidenced by the final weight increase of about 0.25%. Remembering the square root nature of the time axis, it will take approximately five years for this plot to reach 1% as shown. In reality, for flexelement service, the surface-to-bulk ratio of the component will be much less than here, so the shielding effect will be even greater. Furthermore, use of sea water at 100 [degrees] C is a huge acceleration on rates appropriate to actual service temperature.

Preliminary assessment of new curative system

A recently developed ultra fast accelerator, 2,2'-dithio(ethyl ammonium)-bis(dibenzyl dithiocarbamate) has recently been incorporated into an EV system with masterbatch 1 (75/25 NR/PB 950) (see table 10). As well as curing quite rapidly, the Arrhenius-type plot of the scorch times produced from these data has a steeper slope than for most of the other compounds, with a lower log rate level throughout. Consequently, its shelf life plot crosses the target line just below X in figure 1 - the target point for 23 [degrees] C. This result gives a good indication that an improved PLTC in terms of the combination of relatively-short cure time and adequate shelf life for the application in mind should be possible.

Conclusions

The successful development of premium duty natural robber sulfur-cure compounds curable at 70 [degrees] C, and hence associated with reduced manufacturing energy and thus environmental costs, has been achieved. Ultra-fast accelerators mentioned here and liquid polybutene are essential ingredients. Good magnitudes of properties relevant to the high-duty offshore oil platform application which provided the focus of the project were achieved, including tensile properties, tear strength, air-aging resistance, rubber-to-steel bonding, crack growth fatigue and compressive creep. In some cases, the PLTC property levels have surpassed those of the high-temperature-cured NR control compound, the material currently used for this application.

Table 1 - NR/polybutene masterbatch
formulation

Compound                         I

Natural rubber, SMR CV60        75
PB 950                          25
Zinc oxide                       5
Stearic acid                     2
Carbon black, HAF (ASTM N330)   45
Antioxidant/antiozonant, 6PPD    3
Antiozonant wax                  2
Table 2 - first NR/polybutene formulations and
curemeter data

Compound               A       B       C      D *      E

Masterbatch I        157.9   157.9   157.9   157.9   157.9
Sulfur                 1.3     1.3     1.3     1.3     1.3
MBTS                   0.2     0.3      --      --      --
Inhibitor E             --      --     0.2   0.2 *      --
Inhibitor G             --      --      --      --     0.2
ZDBCX                  2.0     2.0     2.0     2.0     2.0
ZIX                    2.0     2.0     2.0     2.0     2.0
[t.sub.2], (40
 [degrees] C) min.     100    90.8    88.6     219     115
[t.sub.2], (70
 [degrees] C) min.    9.30    12.8    11.8    14.7    11.4
[t.sub.2], (100
 [degrees] C) min.     2.2     3.4     2.3     2.7     2.1
[t.sub.95], (70
 [degrees] C) min.    88.0    68.6      67      62      54

* Retarder melted by milling at appropriate high temperature
Table 3 - NR/polybutene formulations and
curemeter data

Compound                                    F              G

Masterbatch I                              157.9          157.9
Sulfur                                       1.3            1.3
Inhibitor E                                2.0 *             --
Inhibitor G                                   --          2.0 *
ZDBCX                                        2.0            2.0
ZIX                                          2.0            2.0
[t.sub.2], (40 [degrees] C) min.             950            351
[t.sub.2], (70 [degrees] C) min.            25.6           20.5
[t.sub.2], (100 [degrees] C) min.            3.3            4.0
[t.sub.95], (70 [degrees] C) min.  [much greater  [much greater
                                   than] 180 (+)  than] 180 (+)

* Retarders melted by milling at appropriate high temperatures

(+) Values applying at maximum time limit of curemeter trace;
  marching moduli
Table 4 - formulation and curemeter data for
Compound H

Compound                                H

Masterbatch I                         157.9
Sulfur                                 2.25
MBTS                                   0.2
ZDBCX                                  0.5
ZIX                                    0.5
[t.sub.2], (40 [degrees] C) min.       578
[t.sub.2], (70 [degrees] C) min.       26.0
[t.sub.2], (100 [degrees] C) min.      4.91
[t.sub.95], (70 [degrees] C) min.      107
[t.sub.max], (70 [degrees] C) min.     228
Table - 5 mechanical properties of Compound B

(69 min. @        Weight   Modulus at     Tensile
70 [degrees] C)   change  100% strain,   strength,
                              MPa           MPa

1 unaged            --        1.8           20.8
2 2 x [t.sub.95]
 cure               --     2.0 (+8.2%)  21.1 (+1.5%)
Postcure
3 Aerobic          0.8%    2.8 (+50%)   15.4 (-26%)
4 Anaerobic         --     2.9 (+55%)   17.0 (-18%)
Aged
5 Aerobic          1.5%    4.4 (+136%)   6.3 (-70%)
6 Anaerobic         --     3.7 (+101%)   7.3 (-65%)

(69 min. @        Elongation      Trouser    Hardness,
70 [degrees] C)   at break, %      tear,        IRHD
                                   N/mm

1 unaged              542          31.9          56
2 2 x [t.sub.95]
 cure             570 (-5%)    11.1 (-65%)     56 (0)
Postcure
3 Aerobic         383 (-29%)   11.5 (-64%)  59.5 (+3.5)
4 Anaerobic       404 (-25%)    7.3 (-77%)    61 (+5)
Aged
5 Aerobic         142 (-74%)    3.1 (-90%)  66.5 (+10.5)
6 Anaerobic       170 (-69%)    4.4 (-86%)  62.5 (+6.5)
Table 6 - mechanical properties of the control compound

(15 min.*)        Weight   Modulus at     Tensile
                  change  100% strain,   strength,
                              MPa           MPa

1 Unaged            --        1.95          24.3
2 2 x [t.sub.95]
 cure               --     3.0 (+54%)   19.7 (-19%)
Postcure
3 Aerobic          2.4%    4.2 (+115%)   7.5 (-69%)
4 Anaerobic         --     3.0 (+52%)   13.3 (-45%)
Aged
5 Aerobic           --     5.0 (+156%)  16.3 (-33%)
6 Anaerobic         --     4.7 (+143%)  13.1 (-46%)

(15 min.*)        Elongation     Trouser      Hardness,
                   at break,      tear,         IRHD
                       %          N/mm

1 Unaged              561         29.3           63
2 2 x [t.sub.95]
 cure             404 (-28%)    7.6 (-74%)     68 (+5)
Postcure
3 Aerobic         158 (-72%)    6.4 (-78%)     70 (+7)
4 Anaerobic       280 (-50%)    6.7 (-77%)   70.5 (+7.5)
Aged
5 Aerobic         265 (-53%)   10.6 (-64%)   73.5 (+10.5)
6 Anaerobic       226 (-60%)   11.3 (-61%)     74 (+11)

* At its normal high curing temperature
Table 7 - additional background on Chemlok
materials

Chemlok 205 is a general purpose metal primer used
with a variety of adhesive topcoats to provide adhesion
and corrosion resistance to the metal substrate.

Chemlok 234B is one of the topcoats that is used over
Chemlok 205. The Chemlok 234B can be used in rubber
lining where the lined component is cured in an autoclave.
It is often used with chlorobutyl compounds, but
works with NR also.

Chemlok 289/290 is a system approach with the Chemlok
289 being a primer (similar to Chemlok 205) and the
Chemlok 290 is the adhesive. This system is used for
rubber lining where the cures are done either in an autoclave
or in pressureless steam cures. The Chemlok
289/290 cures via a diffusion mechanism, while the
Chemlok 234B requires a much higher activation temperature
and thus is best suited for autoclave cures in
the 150 [degrees] C range.

Chemlok 286 is a tacky tie cement that is used when
rubber lining with natural rubber. It is not recommended
to mix the systems, thus Chemlok 205 should be used
together (with 286 for NR) and the 289/290 should be
used together (with 286 for NR).
Table 8 - mechanical properties of Compound H and control

                   Modulus
                   at 100%   Tensile   Elongation  Trouser  Hardness,
                   strain,  strength,   at break,   tear,     IRHD
                    MPa       MPa          %        N/mm

Compound H          2.7       21.2        516       37.8       53
Control
 (15 min. cure *)   3.2       22.1        443       21.5       67
Control
 (4 hr. cure *)     3.5       19.2        369        8.9       66

* At its normal high curing temperature
Table 9 - tear strength of Compound H and control

Sample  Strength,    T      Sample     Strength,   T      Sample
No.       N/mm     kJ/m2      No.        N/mm     kJ/m      No.

Ha       31.6      153.4  Control 15a    22.2      2    Control 4ha
Hb       38.6      214.6  Control 15b    17.7     89.6  Control 4hb
Hc       29.6      138.4  Control 15c    21.4     64.1  Control 4hc
H        33.3      168.8  Control 15     20.4     83.3  Control 4h
Mean T                      Mean T                79.0    Mean T

Sample  Strength,    T
No.       N/mm     kJ/[m.sup.2]

Ha        22.2        17.2
Hb        17.7        30.1
Hc        21.4        26.8
H         20.4        24.7
Mean T

N.B. control 15 = 15 minute cure at its normal high curing
temperature; 4h = 4 hour ditto.
Compound H cure 4 hours @ 70 [degrees] C;. a,b,c signify replicate
testpieces
Table 10 - formulation and curemeter data for
Compound I

Compound                                 I

Masterbatch I                          157.9
Sulfur                                  0.5
P25 PM75                                3.33
SAA30 PM50                              2.0
[t.sub.2], (40 [degrees] C) min.       3,350
[t.sub.2], (70 [degrees] C) min.        109
[t.sub.2], (100 [degrees] C) min.       10.0
[t.sub.95], (70 [degrees] C) min.       314
[t.sub.max], (70 [degrees] C) min.      424

References

(1.) M. Hogan, proceedings of "Oilfield Engineering With Polymers," conference, London, publ. MERL, Hertford, U.K., pp. 188-199 (1998).