Effect of Surface‐Modified Cellulose Nanofibers on the Properties of High Solid Content HMX Propellants

High solid content nitramine propellants are attractive for high‐chamber‐pressure tank weapons because of their high energy density, but their low‐temperature mechanical reliability remains limited. In this work, cellulose nanofibers (CNFs) were surface‐modified with cetyltrimethylammonium bromide (CTAB), oleic acid (OA), and 3‐aminopropyltriethoxysilane (APTS), and introduced at 0.5 wt.% into an octogen (HMX) nitramine propellant. Their effects on thermal decomposition, combustion behavior, and mechanical properties were then examined. Structural characterization confirmed that all three treatments altered the CNFs surface chemistry and improved compatibility with the nitrocellulose/plasticizer matrix. DSC and TG results showed that CNFs incorporation did not noticeably change the main decomposition sequence or overall thermal stability of the propellant system. Closed‐bomb tests likewise indicated only limited changes in overall combustion behavior, while temperature remained the dominant factor controlling the burning response. By contrast, the mechanical effect of CNFs was more evident under low‐temperature conditions. Among the modified samples, CTAB‐CNF showed the highest average impact strength at −40°C, increasing it from 4.10 kJ m − 2 to 5.05 kJ m − 2 . The observed behavior may be associated mainly with interfacial effects introduced by CNF surface modification. These results show that tailoring CNFs surface chemistry is a feasible way to improve the low‐temperature mechanical reliability of high solid content nitramine propellants without sacrificing their intrinsic thermal and combustion characteristics.