A well-dispersed and uniformly shaped detonation nanodiamond (DND) was produced and coated over micron scale RDX in various amounts to form four kinds of DND coating composites (NDRs). In order to confirm the optimal coating amount and its effect on the thermal properties, the thermal decomposition and kinetics were studied by DSC, TG and DPTA techniques. The critical temperature of thermal explosion (T_b) and the self accelerating decomposition temperature (T_SADT) both exhibit an interesting volcano-shaped changing trend and rank in an increasing order of NDR4 < NDR1 < RDX < NDR3 < NDR2. This indicates that the DND coating amount, ranging from 1/7 to 1/5, provides NDRs with better thermal safety than RDX. The thermolytic kinetic parameters (E_a and A) and activation thermodynamic parameters (ΔS^≠, ΔH^≠ and ΔG^≠) are sorted in the following order: NDR1 < NDR4 < NDR2 < NDR3. The gas emission and reaction rate constant of the initial thermal decomposition have the same order. The results show that the DND coating could improve the reactivity of the NDRs and the effect is proportional to the coating amount. However, excessive coating that is more than 1/3 conversely hinders decomposition and gas diffusion, like a layer of protective shell. The isoconversional activation energy (E_a) varies with the conversion extent (α) at the initial stage of α = 0.1–0.5, which indicates that the thermal decomposition of the NDRs is a multi-step process including the secondary reaction or catalytic reaction. However, the E_a values are almost independent of α when α = 0.6–0.9, with the mean values in an increasing order of NDR1 < NDR4 < NDR2 < NDR3.

Flame-retardant rigid polyurethane foams incorporating N,N-(pyromellitoyl)-bis-l-phenylalanine diacid ester glycol have been prepared. After adding N,N-(pyromellitoyl)-bis-l-phenylalanine diacid ester glycol, the density and compressive strength of the polyurethane foams were seen to decrease. The flame retardancy of the polyurethane foams has been characterized by limiting oxygen index, upper limit–94, and cone calorimeter tests. The polyurethane foam with 2.27 wt% N,N-(pyromellitoyl)-bis-l-phenylalanine diacid ester glycol gave a highest limiting oxygen index of 33.4%, and the peak heat release rate of polyurethane foam reduced to 19.5 kW/m² from 47.6 kW/m² of PU-0 without N,N-(pyromellitoyl)-bis-l-phenylalanine diacid ester glycol. Upper limit–94 revealed N,N-(pyromellitoyl)-bis-l-phenylalanine diacid ester glycol did not change the burning rating, and all polyurethane foams had passed V-0 rating. The thermal stability of polyurethane foams has been investigated by thermogravimetric analyzer. N,N-(pyromellitoyl)-bis-l-phenylalanine diacid ester glycol significantly increased the initial decomposition temperature of polyurethane foams and their residues. In addition, the morphology of residual char from the flame-retarded polyurethane foams after cone calorimeter tests has also been characterized by digital photographs. The results indicated that N,N-(pyromellitoyl)-bis-l-phenylalanine diacid ester glycol significantly enhanced the strength and compatibility of the char layer formed by the polyurethane foams. These results indicate that N,N-(pyromellitoyl)-bis-l-phenylalanine diacid ester glycol can improve both the quality and quantity of the char, which has a significant effect on the flame-retardant properties of the foam.

A well-dispersed micron-scale detonation polycrystalline diamond (DPD) was prepared and modified on RDX particles, preparing four DPD-modified RDX (DMR) composites with the modification amount increasing from 1/9 to 1/3. The effect of modification on the thermal decomposition and kinetics of RDX was studied using dynamic pressure measuring thermal analysis (DPTA), differential scanning calorimetry (DSC) and thermogravimetric analysis (TG) techniques. As the modification amount increased, the gas emission, reaction rate constant, decomposition temperature, and kinetic and thermodynamic parameters of the composites increased firstly and decreased afterwards. The DPD had a catalytic effect on the thermal decomposition of RDX, but this effect was not in linear correlation with the modification amount. The DPD-modification amount of 1/7 had the optimal catalytic effect. For DPD modification of less than 1/7, the thermal decomposition of RDX was accelerated by DPD. As the modification amount exceeded 1/7, the excessive DPD modification conversely hindered the decomposition of RDX. The thermal decomposition kinetics demonstrated that the thermal decomposition of the DMRs conformed to a multi-step reaction mechanism involving a catalytic reaction and a secondary reaction, while they had the same rate-determining step, which is the scission of the N–NO₂ bonds of RDX. The DPD modification changes the reaction pathway and reaction rate to affect the decomposition mechanism and kinetics.