Nacre-inspired interface structure design of polymer bonded explosives toward significantly enhanced mechanical performance

Peng Wang,You-long Chen,Li Meng,Yin-shuang Sun,Yu Dai,Xin Li,Jie Chen,Zhi-jian Yang ,Guan-song He

Institute of Chemical Material,China Academy of Engineering Physics,Mianyang,621900,China

Keywords:Polymer bonded explosives Nacre-like structural layer Graphene Cellulose Mechanical properties

ABSTRACT Realizing effective enhancement to the structure of interface region between explosive crystals and polymer binder plays a key role in improving the mechanical properties of the current polymer bonded explosives (PBXs).Herein,inspired by the structure of natural nacre which possesses outstanding mechanical performance,a kind of nacre-like structural layer is constructed in the interface region of PBXs composites,making use of two-dimensional graphene sheets and one-dimensional bio-macromolecules of cellulose as inorganic and organic building blocks,respectively.Our results reveal that the constructed nacre-like structural layer can effectively improve the interfacial strength and then endow the PBXs composites with significantly enhanced mechanical properties involving of creep resistance,Brazilian strength and fracture toughness,demonstrating the obvious advantage of such bioinspired interface structure design strategy.In addition,the thermal conduction performance of PBXs composites also exhibits noticeable enhancement due to the remarkable phonon transport capability endowed by the asdesigned nacre-like structural layer.We believe this work provides a novel design route to conquer the issue of weak interfacial strength in PBXs composites and greatly increase the comprehensive properties for better meeting the higher requirements proposed to the explosive part of weapon equipment in new era.

1.Introduction

Polymer bonded explosives (PBXs) consisting of ultrahighcontent explosive crystals (90-95% by weight) and small amount of polymer binder,are now widely used in both military and civil fields on account of their well-balanced high energy,good safety and easy-processing performance [1,2].However,the mechanical incompatibility between explosive crystals and polymer binder often makes the interface region of PBXs composites as the main weak points.As a result,the cracks and damage are possibly generated in the interface region during the storage,transportation and application processes which will severely threatens the use reliability and safety of the weapon systems[3,4].Hence,in order to further dramatically increase the environmental adaptability of the PBXs composites and better meet the higher requirements proposed to the explosive part of weapon equipment in new era,one of the key points is to greatly increase the mechanical strength of interface region in PBXs composites.

In recent years,considerable efforts have been devoted to strengthening the interfacial interactions of PBXs composites and one of the effective ways is to chemically modify the explosive crystals,endowing them with some specific functional groups which can form strong bonding interactions with polymer binder molecules[2,5-16].Among those chemical modification strategies,employing thein-situpolymerization of dopamine approach has attracted a lot of attentions of the scientific researchers,which not only possesses the advantages of facile preparation,good coating effect and strong interfacial interactions,but also provides a large amount of reaction sites derived from the resultant polydopamine(PDA) molecules for further chemical modification.He et al.used PDA to coat 1,3,5-triamino-2,4,6-trinitrobenzene (TATB) crystals and the results showed that the PBXs composites containing the TATB crystals coated with PDA exhibited largely improved mechanical properties (tensile and compression strength,etc.)due to the enhanced interfacial interactions between TATB crystals and polymer binder [2].Lin et al.had coated three kinds of explosive crystals which included TATB,2,6-diamino-3,5-dinitropyrazine-1-oxide (LLM-105) and 1,3,5,7-tetranitro-1,3,5,7-tetrazocane (HMX)with PDA and the subsequent fabricated PBXs composites also presented enhanced mechanical properties [11].Moreover,when some specific polymer chains such as hyperbranched polymer molecules were grafted onto PDA layer,the interfacial interactions could be further enhanced,leading to the higher improvement efficiency in mechanical properties of PBXs composites [12,14,15].Despite those progresses,the relatively weak constructed interfacial interactions(such as hydrogen bonding,polar interactions etc.)and poor intrinsic mechanical strength of the introduced interfacial reinforcing agent are not desirable for optimizing the structure of interface region.It is still in high demand to develop a novel effective strategy for significantly improving the strength of the interface structure.

In nature,a lot of composites exhibit one or more intrinsic unique superior properties mainly resulting from their special components and structures.Absorbing inspirations from those natural composites,many advanced functional materials have been designed and fabricated successfully.Nacre,due to its integration of extraordinary strength and toughness resulting from the highly ordered brick-and-mortar arrangement of inorganic tablets of calcium carbonate(95 vol%)and organic biomacromolecules(5 vol%),has promoted the constructions of a series of nacre-mimic composites with remarkable mechanical performance thus far[17-25].Based on the outstanding mechanical,thermal and electrical properties,graphene as well as its derivatives have been extensively used as ideal inorganic building blocks for constructing nacre-like materials [19-27] and the final obtained materials always exhibit far superior mechanical performance including strength and toughness than that of natural nacre[25-27].On the other hand,the biomacromolecules of cellulose contains a large amount of hydroxyl groups which can form strong interactions with other materials.In addition,cellulose also exhibits the advantages of high specific strength and modulus,good biocompatibility and low cost.Thus,many researchers have adopted the cellulose molecules as the superior organic building blocks to construct artificial nacre-like materials [25-29].Considering the intrinsic weak mechanical strength of the interface structure of PBX composites,constructing strong and tough nacre-like structure in the interface region is expected to be a promising way for significantly improving the mechanical performance of PBX composites.

In the current study,we have successfully designed and fabricated a novel nacre-like structure(NLS)layer in the interface region of PBXs composites.The graphene sheets and cellulose were used as inorganic and organic building blocks,respectively.By optimizing the compatibility of NLS layer to the explosive crystals as well as the relative contents of building blocks in NLS layer,remarkable improvement in mechanical performance of PBXs composites was achieved only with quite a few amount loading of graphene and cellulose.This work provides a new avenue to conquer the issue of weak interfacial strength in PBXs composites and greatly increase the mechanical properties for better meeting the high requirements proposed to the explosive part of weapon equipment in new era.

2.Experimental section

2.1.Materials

TATB crystals with particle size about 20 μm were provided by Institute of Chemical Materials,CAEP,China.The copolymer of vinylidene fluoride (VDF) and chlorotrifluoroethylene (CTFE) used as the polymer binder was provided by Zhonghao Chenguang Chemical Industry Co.,Ltd.China.The water soluble graphene sheets with about 5 μm in width and 2 nm in thickness were purchased from Deyang Xitan Nano Technology Co.,Ltd.China which was shown in Fig.S1 in supporting information.The cellulose molecules prepared with the TEMPO-Mediated Oxidation method were purchased from Tianjin Woodelf Biotechnology Co.,Ltd.Dopamine hydrochloride and(hydroxymethyl)aminomethane(Tris,99%) were provided by Sigma-Aldrich.The other reagents of analytical grade were commercially purchased and all the materials and reagents were used as received.

2.2.Construction of NLS layer

First,the TATB crystals were coated with PDA molecules through the in situ surface polymerization of dopamine strategy according to the previous study[2].Then the PDA coated TATB(pTATB)were added into the aqueous solution containing the mixture of graphene sheets and cellulose molecules.After vigorous stirring for 2 h,the aqueous solution was heated to 90 ℃ to distill the water under stirring.When most of the water evaporated,the products were transformed into a vacuum oven at 60 ℃ for 24 h to remove the residual water.Through this way,the NLS layer was constructed on the surface of TATB crystals and the structure of NLS layer can be easily tuned by changing the mass ratio of graphene to cellulose.

2.3.Preparation of PBXs composites

The typical water suspension method was used to prepare PBXs composites for the subsequent hot compression molding process[2,30].After the addition of polymer binder,the final PBXs composites with the NLS layer in the interface region between explosive crystals and polymer binder could be obtained.Subsequently,the products were subjected to a hot compression molding process under 120 ℃ and 400 MPa for 5 min to get the final PBXs composites (named as PBX-N composites) for further characterization and study.For comparison,the pure PBXs composites with only TATB crystals and polymer binder (named as PBX-0 composites)and PBXs composites with pTATB crystals and polymer binder(named as PBX-P composites)were also prepared.For all the PBXs composites,the contents of the explosive crystals were fixed as 95 wt% while the contents of other materials which include polymer binder,PDA layer and NLS layer were 5 wt% in total.

2.4.Characterization

The morphologies of the explosive crystals and PBXs composites were characterized with Field-Emission Scanning Electron Microscope (FESEM,JSM-6390LV,Zeiss).The Brazilian tests were analyzed using a universal testing machine (INSTRON 5582) at ambient temperature and the dimension of the specimen was 20 × 6 mm2(diameter × thickness).The creep properties of the PBXs composites were conducted by a dynamic mechanical analyzer (DMA 242C,Netzsch,Germany) with a three-point bending sample holder.The dimension of the specimen was 30 × 10 × 1.5-2 mm3(length × width × thickness).The thermal conductivity of the PBXs composites was tested by a 2500S Hot-Disk thermal constant analyzer with sample dimension of 20 × 6 mm2(diameter × thickness).

3.Results and discussion

3.1.Construction of NLS layer in the interface region of PBX-N composites

The construction process of NLS layer in PBX-N composites was schematically shown in Fig.1.In order to improve the compatibility of NLS layer to the explosive crystals,the TATB crystals are first coated with polydopamine (PDA) molecules through thein-situpolymerization of dopamine strategy according to the previous study[2].The water-soluble graphene sheets and cellulose are used here to guarantee their uniform dispersion states in the aqueous system.Moreover,the oxygen-containing groups of graphene sheets and cellulose are quite helpful for forming strong interfacial interactions with PDA molecules (indicated by the Fourier transform infrared spectra characterization in Fig.S1 in Supporting Information).During the mixing and distillation processes,the formation of strong π-π interactions,hydrogen bonding,etc.among PDA,graphene sheets and cellulose are expected to contribute to the adhesion of both graphene sheets and cellulose to the surface of pTATB crystals,which is beneficial to the formation of NLS layer [19,21,24].With further addition of polymer binder,the NLS layer is successfully constructed in the interface region between TATB crystals and polymer binder system targeted enhanced mechanical properties of the PBX-N composites after hot compression procedure.

The construction of NLS layer can change the surface morphologies of TATB crystals.As shown in Fig.2(a),the neat TATB crystals present relatively flat and smooth surface structure.After being coated by PDA molecules,the surface of pTATB crystals become rough and curled due to the formation of PDA aggregates(Fig.2(b))[2,12].With the addition of graphene sheets(marked as pTATB-G),as displayed in Figs.2(c) and 2(d),due to the strong hydrogen bonding and π-π interactions between graphene and PDA molecules,the graphene sheets are tightly adhered to the surface of explosive crystals (indicated by the red arrows in Fig.2(d)),which is the prerequisite for enhancing the compatibility between explosive crystals and the subsequent constructed NLS layer.After further incorporation of cellulose molecules(marked as pTATB-NLS),benefiting from the oxygen-containing groups of graphene sheets and cellulose,hydrogen bonding interactions are also formed in between them,which make the cellulose molecules tightly wrap the graphene sheets (as presented in Figs.2(e) and 2(f),the red and green arrows in Fig.2(f) indicate the graphene sheets and cellulose,respectively),forming a dense brick and mortar microstructure and completing the construction of NLS layer on the surface of TATB crystals.On the other hand,in the absence of PDA coating layer (marked as TATB-NLS),as shown in Figs.2(g) and 2(h),the interfacial interactions between NLS layer and TATB crystals are quite weak which cause the graphene sheets and the cellulose(indicated by the red and green arrows in Fig.2(h),respectively) almost detach from the TATB crystals.Thus,the results directly demonstrate the PDA coating layer is important to improve the compatibility of NLS layer to the explosive crystals.

The effect of constructed NLS layer to the chemical structure of the explosive crystals were investigated by FTIR and Raman spectra characterizations.As shown in Fig.3(a),for pure TATB,the characteristic peaks of FTIR spectrum at 3206 and 3313 cm-1are respectively attributed to the symmetric and asymmetric stretching vibrations of -NH2group while the stretching vibration of-NO2group appears at 1323 cm-1[13-15].After coating PDA and further construction of NLS layer,the corresponding explosive crystals exhibit the similar FTIR spectra due to the strong absorption effect of pure TATB crystals.However,the intensities of characteristic peaks at 1323,3206 and 3313 cm-1decrease especially for pTATB-NLS crystals owing to the coating effect of NLS layer which does not possess the above the characteristic absorption peaks.Furthermore,the Raman spectra provide further evidence of the coating effect of PDA and NLS layer.As shown in Fig.3(b),after modification,the intensities of the characteristic peaks of pure TATB including nitro groups are significantly weakened,especially for pTATB-NLS crystals,because of the absence of nitro groups in NLS layer,indicating the successful construction of NLS layer on the surface of explosive crystals.

Fig.3.(a) FTIR and (b) Raman spectra of TATB,pTATB,and pTATB-NLS crystals.

3.2.Surface properties

In order to investigate the compatibility of NLS layer to polymer binder,the contact angle measurements were conducted to characterize the surface properties of the corresponding explosive crystals.As shown in Fig.4,for pure TATB crystals,the contact angles of water and diiodomethane are 80.57°and 30.25°,respectively,indicating the low wettability to water due to the low surface energy and non-polar characteristic [2,12,14].After modification with PDA,the corresponding water contact angle slightly decreases while diiodomethane contact angle slightly increases,as the PDA coating layer endows the TATB crystals with a large amount of hydrophilic functional groups including catechol,amine and imine [2,12].With the further addition of graphene sheets,the water contact angle increases while diiodomethane contact angle decreases,compared with that of pure TATB crystals.This may be possible due to the non-polarity of the introduced graphene sheets.When the NLS layer is finally constructed on the explosive crystals,due to the graphene sheets are the main components of NLS layer,the results show that the water and diiodomethane contact angle of pTATB-NLS crystals are closed to which of pTATB-G crystals,revealing that the non-polarity of pTATB-NLS crystals is also enhanced to certain extent.

Fig.4.Contact angle measurements with test fluids of water and diiodomethane for TATB,pTATB,pTATB-G,and pTATB-NLS crystals.

Furthermore,the surface tensions of the explosive crystals as well as the interfacial adhesive work between explosive crystals and polymer binder can be quantitatively calculated exploiting the geometric mean equation and harmonic average equation [2].The as-obtained results were listed in Table S1.It can be seen that,after coating PDA layer,the dispersion component (γd) decreases while polarity component (γp) increases compared with that of pure TATB,resulting in bigger polarity difference between pTATB and non-polar polymer binder,which is not helpful for enhancing the interfacial adhesion work based on the principle of polarity similarity [14].On the other hand,when the NLS layer is further constructed,the results are opposite,for which γdincreased and γpdecreased,indicating the improved compatibility between pTATBNLS crystals and non-polar fluoropolymer.Accordingly,the remarkable mechanical performance of NLS layer combined with the good interfacial compatibility are expected to dramatically enhance the interfacial strength of PBXs composites.

3.3.Mechanical properties

As mentioned above,the weak interfacial strength is one of the main issues which results in the poor mechanical performance of PBXs composites.Here,the effect of the constructed NLS layer to the mechanical performance of PBXs composites was investigated in detail.The creep resistance property is directly related to the dimensional stability of the PBXs composites,which is quite important for the security and reliability of the weapon system.Fig.5(a) shows the creep behaviors of the PBXs composites under the stress of 4 MPa and the temperature of 25 ℃.As displayed,all the PBXs composites do not present creep failure with the applied test condition for 90 min.With the coating of PDA molecules,the creep strain of PBX-P composites decrease obviously due to the enhanced interfacial interactions,which is consistent with the previous reports[2,12].Moreover,after further construction of NLS layer with only 0.5 wt% content,the creep strain of the PBX-N composites decreases further as well.When the mass ratio of graphene to cellulose is 9 : 1,an optimized creep resistance performance was achieved(marked as PBX-N(9-1)in Fig.5(a)),with the creep strain of less than 0.01%,demonstrating the greatly improved dimensional stability compared with that of PBX-0 composites for which the creep strain was about 0.02%.The best mass ratio of graphene to cellulose for the enhancement of the creep resistance properties of the PBXs composites is also similar to that of the natural nacre which consists of 95 vol% inorganic calcium carbonate and 5 vol% organic biomacromolecules [20],indicating the effectiveness of the bioinspired interface structure design strategy.

Fig.5.(a)Creep strain curves;(b)Brazilian stress-strain curves;(c)Comparison of Brazilian performance and(d)fracture toughness of the PBX composites.The total content of NLS layer was 0.5 wt%.

The tension performance of the PBXs composites is also crucial for structure integrity of the weapon system.As shown in Fig.5(b),the representative stress-strain curves of PBXs composites were obtained from Brazilian test.It can be seen that,after the modification of PDA,both the Brazilian strength and the fracture strain are increased to some degree,due to the enhanced interfacial interactions between explosive crystals and polymer binder.After the further incorporation of NLS layer,the Brazilian strength and fracture strain continued to increase greatly.The best improvement efficiency in tension performance is also obtained under the mass ratio of graphene to cellulose of 9 : 1 and the corresponding Brazilian strength and fracture strain are dramatically increased to 9.26 MPa and 0.28%,which are 51.1% and 55.6% higher than those of PBX-0 composites,respectively.The enhancement efficiency in Brazilian performance of PBX-N composites is also superior in contrast to most of other PBXs composites reported previously except for the example which required quite tedious and complex preparation procedures (Fig.5(c)) [14],demonstrating the advantage of the bioinspired interface structure design strategy proposed in this study.In addition,the fracture toughness of the PBXs composites can be figured out by integrating the stress-strain curves[31,32] and the corresponding results are shown in Fig.5(d).It is clearly seen that through constructing the NLS layer,the toughness of PBXs composites are significantly improved with a maximum enhancement efficiency of 127.3% for PBX-N (9-1) composites compared with PBX-0 composites.Those results have thoroughly signified the superiority of the bioinspired interface structure design strategy proposed in this study.To further illustrate that the superior mechanical performance of PBX composites was ascribed to the successful construction of NLS layer of NLS layer to the explosive crystals,the creep and Brazilian tests were also conducted for the PBXs composites with sole graphene and cellulose.As shown in Fig.S2,the corresponding PBXs composites only present quite limited improvement efficiency in creep and tension properties,indicating that the superior mechanical performance of PBX-N composites is ascribed to the synergistic enhancing effect from the combination of graphene and cellulose.In another word,the NLS layer constructed in the interface region of PBX-N composites plays a key role in improving the mechanical performance.Moreover,the PBXs composites without PDA coating layer were also fabricated and the corresponding mechanical properties(shown in Fig.S2) were much inferior to which of PBX-N (9-1)composites.The results directly indicate that the presence of PDA coating layer could improve the interfacial compatibility of the constructed NLS layer to the explosive crystals,which is also important for achieving superior mechanical performance.

To study the mechanical behavior of the corresponding PBXs composites in deeply,the morphologies of the fracture surface after Brazilian test were characterized through FESEM method which are shown in Fig.6.As displayed in Figs.6(a)and 6(b),for PBX-0 composites,a large amount of smooth explosive crystals(marked by the red arrows) as well as big cracks (indicated by the red curve in Fig.6(a)) are exposed,indicating the occurrence of interfacial debonding between explosive crystals and polymer binder resulting from the weak interfacial strength.After being coated with PDA(as shown in Fig.6(d)and 6(e)),the interfacial bonding strength is improved which resulted in the less exposed TATB crystals,smaller cracks (marked by the red oval in Fig.6(d)) and more fracture damages of polymer binder system (marked by the red arrows in Fig.6(e)).With the subsequent construction of NLS layer,notable distinctions can be found clearly in Fig.6(g) and 6(h) for PBX-N(9-1) composites.The NLS layer is tightly adhered to the surface of explosive crystals (marked by the red oval in Fig.6(g)) and no obvious cracks are found.Beyond the NLS layer,the signs of fractured polymer binder molecules are observed (indicated by the blue oval in Fig.6(h)).The above fracture morphologies demonstrate the strong interface structure between explosive crystals and polymer binder in PBX-N composites which can effectively avoid the interface fracture and greatly contribute to the mechanical enhancement of the composites as discussed above.Fig.6(c),6(f)and 6(i) schematically show the reinforcing mechanism of the constructed NLS layer to the PBXs composites.For PBX-0 composites,due to the interfacial incompatibility between TATB crystals and polymer binder,under the stimulation of external force,the cracks are easily ignited and further propagated along the interface region (as shown in Fig.6(c)),leading to the poor mechanical performance.After being coated with PDA,as shown in Fig.6(f),the interfacial bonding strength is enhanced which can inhibit the occurrence and growth of the cracks,thus,resulting in better mechanical properties compared with PBX-0 composites.Finally,with successful construction of NLS layer,as presented in Fig.6(i),the strength of the interface structure is significantly improved which greatly avoids the generation and propagation of the cracks,endowing the resultant PBX-N composites with excellent mechanical performance.

Fig.6.FESEM images of the fracture surface morphologies of (a),(b) PBX-0 composites,(d),(e) PBX-P composites and (g),(h) PBX-N (9-1) composites after Brazilian test,respectively.(b),(e)and(h)are the amplification of(a),(d)and(g),respectively.Schematic representation of the interfacial debonding behaviors of(c)PBX-0,(f)PBX-P and(i)PBXN (9-1) composites.

The finite-element method (FEM) simulations were also conducted to study the mechanical reinforcing effect of the NLS layer to the PBXs composites under uniaxial tension.As shown in Fig.S3,the PBXs composites are modeled by a 2D Voronoi representative volume element in which the volume fractions of the explosive crystals and the binder system are 95% and 5%,respectively.To simplify the simulation,a linear constitutive model was adopted for both the explosive crystals and binder system.The failure of crystal-binder interface was modeled by the cohesive zone model(CZM) approach and a bilinear traction separation law was employed to depict the failure behaviors.This method has been demonstrated to be reasonable and effective to qualitatively analyze the failure of composites,especially for which contain plenty of interfaces.To compare the response of PBX-0 and PBX-N(9-1) under uniaxial tension,stronger interfacial parameters between crystals and binder system were adopted to simulate the strengthening effect of the NLS layer.Material failure parameters used in the simulation are listed in Table S2.The results indicate that with the construction of NLS layer,the strength of both interface region and binder system is dramatically enhanced.For further elucidation of the failure process of the PBXs composites,typical deformation snapshots of the composites during tension process are presented in Figs.7 and S4.As can be seen that,under the similar strain condition,PBX-N(9-1)composites exhibit much better cracks resistant capability compared with that of PBX-0 composites.In terms of PBX-0 composites,obvious cracks start to appear at the strain of 0.168%(as indicated by the blue arrow in Fig.7(b)),while for PBX-N (9-1) composites,before the strain increased to 0.226%,there are no noticeable cracks.The maximum tensile stress during the whole tension process increased significantly from 6.38 MPa of PBX-0 composites to 9.63 MPa of PBX-N(9-1) composites (as exhibited in Fig.S4),which are also closed to their corresponding experimental Brazilian strength (6.13 MPa and 9.26 MPa).The detailed simulation process is presented in the Supporting Information.Thus,here the FEM simulations again demonstrate the superior mechanical performance of PBX-N(9-1)composites,which should also be assigned to the delicately designed NLS layer as discussed above.

Fig.7.Typical deformation snapshots of PBXs during tension process: (a)-(d) PBX-0 and (e)-(h) PBX-N (9-1) composites.

3.4.Thermal conduction performance

Apart from the mechanical performance,improving the thermal conduction performance is also highly desirable for enhancing the environmental adaptability of PBXs composites [3,33-35].Here,the thermal conduction properties of PBX-N composites were also investigated due to the introduction of highly thermally conductive graphene sheets.As presented in Fig.8(a),with construction of NLS layer,the PBX-N composites exhibit noticeable increase in thermal conductivities.For PBX-N (9.5-0.5) composites,the thermal conductivity reaches up to 0.956 W m-1K-1,the value of which is 37.0% higher than that of pure PBXs composites.Interestingly,the thermal conduction performance of PBX-N composites is superior compared with that of the corresponding PBXs composites with sole graphene sheets(named as PBX-G composites).As reported in previous study,the nacre-like layer by layer structure benefits to form continuous conductive pathways where the phonons can transfer effectively while in the composites with random graphene dispersion state,the phonons are hard to migrate [36,37].This is owing to the higher thermal conductivities of PBX-N composites(as shown in Fig.8(b)).Constructing the NLS layer in PBXs composites not only dramatically increases the mechanical performance,but also exhibits good potential to improve the thermal conduction property,manifesting a quite overwhelming strategy for the fabrication of PBXs composites with remarkable environmental adaptability.

Fig.8.(a)Thermal conductivity of PBX-N composites and the corresponding PBX-G composites with sole graphene;(b)Schematic representation of the phonon transformation in the PBX-N and PBX-G composites,respectively.

4.Conclusions

Here we have proposed a bioinspired interface structure design strategy for greatly improving the mechanical performance of PBXs composites.Inspired by the structure of natural nacre which possesses outstanding mechanical properties,a kind of novel NLS layer is successfully constructed in the interface region of PBXs composites,exploiting graphene sheets and cellulose as the inorganic and organic building blocks,respectively.Our investigation results have shown that the interfacial strength can be largely enhanced after the construction of NLS layer,endowing the PBXs composites with significantly improved mechanical properties.The resultant creep resistance,Brazilian strength and fracture toughness are dramatically increased 51.7%,51.1% and 127.3%,compared with pure PBXs composites in this work and are also superior to most of other PBXs composites reported previously,implying the obvious advantage of this bioinspired interface structure design strategy.In addition,the thermal conduction performance of PBX-N composites also exhibits noticeable enhancement due to the good phonon transport capability endowed by the constructed NLS layer.This investigation paves a new way to the rational design of PBXs composites targeted remarkable mechanical performance and thermal conductivity,which can satisfy the practical demand of the explosive part in weapon equipment.

Associated content

Supporting Information.FTIR spectra of graphene and cellulose,surface tension of TATB,pTATB and pTATB-NLS crystals and the corresponding interfacial adhesive work between explosive crystals and polymer binder,creep strain curves and Brazilian stressstrain curves of the PBXs composites,the schematic of finite element model,failure parameters in CZM for PBX-0 and PBX-N(9-1),typical deformation snapshots of PBXs during tension process.

Notes

The authors declare no competing financial interest.

Declaration of competing interest

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

Acknowledgments

The authors acknowledge the financial support from National Natural Science Foundation of China (Grant No.21875230,22275173,U2030202).

Appendix A.Supplementary data

Supplementary data to this article can be found online at https://doi.org/10.1016/j.dt.2022.10.013.