PIBSI is the primary dispersant in every modern PCMO formulation. In ACEA C-sequence low-SAPS PCMO (S/A ≤0.5–0.8%, S ≤0.3%), PIBSI at 5–8 wt% provides the complete dispersancy function - soot suspension, sludge prevention, varnish inhibition - while consuming none of the SAPS budget. The entire S/A allowance is available for Ca detergents and ZDDP. Higher MW PIBSI (1300+) is preferred for extended drain intervals (20,000–30,000 km OEM approvals for VW 507.00/BMW LL-04) where the dispersancy capacity must last longer. Standard MW (900–1300) is adequate for normal drain intervals in API SP/SN+ PCMO (7,500–15,000 km).

EGR-equipped heavy-duty diesel engines recirculate up to 25% of exhaust gas into the intake, massively increasing soot loading in the crankcase oil - Mack T-12 and Volvo T-13 engine tests specifically measure PIBSI-type dispersant performance under high-EGR soot conditions. High MW PIBSI (>1300) at 6–10 wt% is used in long-drain HDEO to maintain adequate soot-holding capacity across the full drain interval. At 4% soot loading (by weight in oil, the API CK-4 T-13 limit), the dispersant must still maintain oil kinematic viscosity within ≤12 cSt increase at 100°C - a direct measure of the PIBSI's ability to prevent soot-induced viscosity thickening. Higher MW PIBSI provides better viscosity control at high soot concentrations due to the more effective steric barrier of the longer PIB chains.

In gas engine oils (natural gas, biogas, landfill gas), the dominant oil degradation mechanism is not soot (gas engines have very low carbonaceous particulate) but NOₓ-induced nitration - NOₓ blow-by gases react with base oil to form nitro-compounds and nitroester oxidation by-products that increase oil viscosity and form polar deposits on valve train and piston crown surfaces. PIBSI's polar head group (succinimide ring, free –NH/–OH) is well-suited to adsorb these nitrated polar by-products and maintain them in suspension - supplementing the Ca salicylate detergent's surface-cleaning action. In marine TPEO (trunk piston engine oil), PIBSI at 3–8 wt% provides dispersancy in the crankcase sump where combustion by-products (including soot from marine diesel combustion) accumulate over long service intervals of 1,000–4,000 hours.

In long-service industrial lubricants (hydraulic oils ISO VG 32–68, rotary compressor oils, industrial gear oils GL-4/5), PIBSI at 1–4 wt% provides varnish precursor dispersancy - keeping polar oxidation by-products suspended in the bulk oil rather than accumulating as lacquer on servo valve spools, compressor surfaces, or gear tooth flanks. Low PIB MW grades (600–900) are preferred for industrial hydraulic applications where minimum viscosity contribution from the dispersant is desirable. In compressor oils handling process gases (air, N₂, CO₂), the zero-ash, zero-sulphur character of PIBSI ensures the dispersant contributes no decomposition products that could contaminate the process gas stream.

Q: What is the difference between PIB Mono-Succinimide (PIBSI) and PIB Bis-Succinimide? When should each be used?

In PIB Mono-Succinimide (PIBSI), one PIBSA unit is attached to one end of a polyamine chain - leaving the other end with free –NH₂ and –NH groups. In PIB Bis-Succinimide, two PIBSA units react with both ends of the polyamine chain - consuming the free amine groups in a second imidation to form the bis structure. The practical differences: (1) Mono-PIBSI retains more free basic nitrogen groups (un-reacted –NH, –NH₂) per molecule - giving higher basic N content and better performance in applications where polar group interaction with soot and oxidation by-products is the priority, such as standard PCMO and diesel HDEO sludge control; (2) Bis-PIBSI has a more symmetrical structure with lower free amine content but improved shear stability (the two PIB chains make it harder to shear-degrade under high mechanical stress) - preferred in high-shear applications like automatic transmission fluid (ATF), heavy-duty gear oil, and long-drain HDEO where shear stability of the dispersant itself matters. Sinolook supplies both; the next product in this series is PIB Bis-Succinimide.

Q: Why is nitrogen content (N%) the primary specification metric for PIBSI, and how does it relate to dispersancy performance?

Nitrogen content directly quantifies the number of basic polar groups (–NH–, –N<, –NH₂) per unit mass of dispersant - it is these polar groups that adsorb onto soot particles, polar oxidation by-products, and sludge precursors via H-bonding and Lewis acid-base interactions. Higher N% = more polar adsorption sites per gram = stronger dispersancy per kg of additive treated. In bench dispersancy tests (Blotter Spot Test ASTM D7843, Turbiscan soot stability, and engine sequence VH sludge test correlation), N% has the strongest single correlation with dispersancy pass/fail rating among all PIBSI parameters. Note: N% alone is not sufficient to characterise dispersancy - PIB MW must also be specified, since very high N% with very low PIB MW can give poor oil solubility; the optimum is a balanced N%/MW combination for each application viscosity grade and base stock.

Q: Can PIBSI partially replace a metallic detergent to reduce sulphated ash, and are there performance trade-offs?

PIBSI and metallic detergents perform complementary but non-interchangeable functions, so a direct replacement is not straightforward. PIBSI can partially substitute for detergent in one specific scenario: when the motivation is purely sludge/varnish control (Sequence VH performance) and TBN is not the driver - in that case, reducing Ca detergent treat and increasing PIBSI treat can maintain sludge performance while reducing S/A. However, PIBSI cannot replace the TBN (acid neutralisation), surface deposit control (ring belt cleanliness from Sequence IIIG/IIIH), or rust inhibition functions of the Ca detergent. In low-SAPS formulation development, the typical approach is to minimise metallic detergent treat rates (Ca sulfonate + Ca salicylate) to meet the S/A ceiling, then use PIBSI (±borated variant) at higher treat rates to compensate for the dispersancy reduction - rather than replacing one with the other.

Q: Does high MW PIBSI (PIB >2000) always outperform standard MW (PIB 900–1300) in engine tests?

Not universally. High MW PIBSI (>2000) outperforms standard MW in: (1) soot-induced viscosity thickening prevention under high-EGR soot conditions (Mack T-13, Volvo T-13); (2) long-drain dispersancy retention - the larger steric barrier is less likely to be displaced by competing soot particle–soot particle contact at high soot loadings (>3–4 wt%); (3) re-deposition prevention of already-dispersed material. However, standard MW (900–1300) outperforms in: (1) dispersancy at low soot concentrations (the higher N% per kg of lower MW PIBSI means more active sites at equivalent treat rate); (2) Sequence VH sludge (low-soot, polar by-product dominated test - more polar groups matter more than steric barrier size); (3) cold-temperature flow - lower MW = lower treat viscosity = less impact on cold-crank viscosity and MRV viscosity at −35°C. Most HDEO formulations therefore use a blend of standard and high MW dispersant grades to optimise across all these parameters simultaneously.

Ashless Dispersants Series: PIB Mono-Succinimide (PIBSI) ✅ · PIB Bis-Succinimide (next) · Borated PIBSI · Borated Bis-Succinimide · Boron-Phosphated Bis-Succinimide · Low Viscosity Dispersant