Lubricant Additives

294 Lubricant Additives: Chemistry and Applications

viscosity at low temperatures than noncrystalline or amorphous copolymers of similar molecular

weight. For this reason, the class of EP copolymers having ethylene content greater than ∼60 wt%

are often called low-temperature OCPs or LTOCPs. A rheological comparison of two LTOCPs

and one conventional OCP viscosity modifi er in several SAE 5W-30 oil formulations is seen in

Figures 10.10 and 10.11. These data illustrate the low-temperature rheological benefi ts of LTOCPs.

A number of workers have cautioned, however, that the long ethylene sequences of LTOCPs

are similar in structure to paraffi n wax and can interact with waxy base oil components at low

temperatures. In many cases, they require specially designed pour point depressants (PPDs) to

function properly in certain base stocks. Thus, LTOCP viscosity modifi ers have been impli-

cated in problems such as MRV failures in comingled fresh oils [105] and used passenger car

lubricants [106,107].

FIGURE 10.10 Cold cranking simulator (CCS) viscosity for six SAE 5W-30 lubricant formulations, each

blended with one of three viscosity modifi ers: LTOCP1, LTOCP3, or OCP1. Within each base oil type, the

ratio of high and low-viscosity base oils was kept constant.

2000 2500 3000 3500 4000

Sun Tulsa

Exxon

Chevron RLOP

Sun HPO

Mobil Paulsboro

Safety Kleen

CCS viscosity (mPa s) at − 25 °C

LTOCP1

LTOCP3

OCP1

FIGURE 10.11 Mini-rotary viscosity results for six SAE 5W-30 lubricant formulations, each blended with

one of three viscosity modifi ers: LTOCP1, LTOCP3, or OCP1. Within each base oil type, the ratio of high and

low-viscosity base oils and the type and concentration of pour point depressant were held constant.

0 10,000 20,000 30,000 40,000 50,000 60,000

Sun Tulsa

Exxon

Chevron RLOP

Sun HPO

Mobil Paulsboro

Safety Kleen

MRV TP-1 (mPa s) at − 35 °C

LTOCP1

LTOCP3

OCP1

Yield stress failures

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