Preparation And Properties Of Propellant Heat-shrinkable Coating Materials

Loading Solid Propellant coating technology is one of the important directions in the field of propellant charge.For a long time,using the traditional methods such as wrapping and covering to coat Large-diameter ratio propellant will cause many problems including poor quality,low coating efficiency,and many defects in the coating process.In this paper,shape memory polymers were applied in the field of propellant coating,which provides a new idea to solve the coating problems.There are no related reports at home and abroad,so this research is meaningful for military applications.In this paper,LDPE（Low Density polyethylene）,EPDM（Ethylene-Propylene-Diene Monomer）and EVA（Ethylene-vinylacetate copolymer）were used as matrix materials.Flame retardants,antioxidants and processing aids were added into the matrix materials.The heat-shrinkable tube used in propellant field were prepared by blending,extrusion,radiation crosslinking,heat expansion and cooling processes.The performance of blends including Fire-resistant,shape memory,thermal stability,rheological and mechanical properties was evaluated and analyzed.Three parameters in the blending process,mixing temperature,mixing time and rotor speed were optimized by an orthogonal experiment.The results showed that the rotor speed was the most important factor affecting the material properties,followed by the mixing temperature,and the mixing time.Setting the mixing temperature to 135℃,the mixing time to 20 min,and the rotor speed to 100 r/min,the obtained materials have the better mechanical properties.The tensile strength and elongation at break were 18.1 MPa and 740%.The performance of different formulations at different radiation doses had been studied in this article.The results showed that the comprehensive performance of the material was better when 25%decabromodiphenylan（DBDPE）–trioxide（Sb₂O₃）,5%LDPE and 5%EVA-g-MAH were added into the material and then the sample was irradiated with a radiation dose of 120KGy.According to the test results,the limiting oxygen index of the material was27.1,the tensile strength and elongation at break were 25.1 MPa and 742%,the shape fixing rate and shape recovery were 99.2%and 99.0%,and the gel content was 78.9%.Besides,the material has good rheological properties and is easy to process.After optimization of the process and formulation,the extrusion process of the single-screw extruder was simulated by Polyflow software.The effects of screw inner diameter D₁,D₂,screw pitch L and different heating schemes on the extrusion process were studied.Setting the values of D₁,D₂and L to 40mm,58mm and 65mm and using stepwise heating method can help to obtain the sample which has the better quality.The developed coating tube was used to coat propellant and this coating process was properly designed and tested.The results showed that,setting the temperature to 95℃and setting the heating time to 5 min,the heat-shrinkable tube and the propellant could be closely adhered,and the coating quality was very good.