Lubricant Additives

Olefi n Copolymer Viscosity Modifi ers 301

a higher ethylene content (see Figure 10.13). The latter property also manifests itself in lower CCS

viscosity. The MRV viscosity is also lower for OCP1 relative to the other amorphous OCPs, but this

is highly dependent on the particular PPD that was chosen for this study. The fact that most of the

oils displayed yield stress failures at –35°C shows that the PPD was not optimized for this particular

set of components.

As SSI decreases from OCP1 to OCP4, the polymer concentration needed to reach a KV target

of 10 cSt increases. In other words, polymer thickening effi ciency is proportional to shear sta-

bility index. Among the noncrystalline OCPs, increasing polymer level causes the CCS viscosity

to increase. Since all oils were formulated with the same base oil composition, high- temperature

HTHS is relatively constant, independent of OCP type. OCP4, the lowest molecular weight polymer,

should have the lowest degree of TVL, and it indeed has the highest HTHS viscosity of the group.

10.5.4.2 Comparative Study of 37 SSI OCP Viscosity Modifi ers

in an SAE 15W-40 Engine Oil Formulation

In this example, the base oil ratio and polymer concentration were adjusted to achieve the following

targets: KV = 15.0 cSt and CCS = 3000 cP at –15°C. The base stocks were American Petroleum

Institute (API) Group I North American mineral oils, the additive package was of API CH-4 qual-

ity level, and the PPD was a styrene ester type that was optimized for these base oils. All viscosity

modifi ers (see Table 10.7) were nominally 37 SSI according to ASTM D6278. Rheological results

are summarized in Table 10.8.

OCP3 is the same polymer as in Table 10.5. Although OCP8 and OCP9 are semicrystalline

LTOCPs, they represent different manufacturing technologies, broadly described in Figures 10.4

and 10.5, respectively. Incidentally, OCP1 in Table 10.5 was also manufactured by the tubular reac-

tor technology described in Figure 10.5.

TABLE 10.6

Rheological Properties of SAE 5W-30 Engine Oils Containing Different OCP

Viscosity Modifi ers

OCP1 OCP2 OCP3 OCP4

Polymer content (wt%) 0.58 0.71 0.73 1.05

Kinematic viscosity (cSt) at 100°C 10.17 10.09 9.99 10.10

Viscosity index 156 160 160 158

CCS viscosity (cP) at −25°C 3080 3280 3510 3760

MRV viscosity (cP) at −30°C 13,900 26,500 26,700 28,100

MRV viscosity (cP) at −35°C 40,100 Yield stress Yield stress Yield stress

HTHS (cP) 2.95 2.88 2.96 3.07

TABLE 10.7

OCP Viscosity Modifi ers Used in

Rheological Study in Table 10.8

Viscosity Modifi er Code Copolymer Type

OCP7 EPDM, amorphous

OCP3 EP, amorphous

OCP8 EPDM, LTOCP

OCP9 EP, LTOCP

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