| As a new type of engineering material,geocell has a three-dimensional network structure.It was first used in soft foundation areas such as desert and beach.It has excellent mechanical properties,anti deformation ability and strong lateral limiting force.It plays a key role in soft foundation road construction.With the development of society,the application scope of geocell has been further expanded,which plays a role in the reinforcement of railway,dam,slope and other foundations.Therefore,in order to meet the engineering needs,people have further requirements for the performance of geocell materials.Therefore,this subject mainly focuses on how to improve the mechanical properties and tensile strength of welded joints of geocell materials based on HDPE to meet the engineering requirements.Taking high density polyethylene（HDPE）as matrix,nylon6（PA6）as reinforcing phase and HDPE grafted maleic anhydride（HDPE-g-MAH）as compatibilizer,an orthogonal experimental table of three factors and four levels L16（43）was designed.The geocell composites were obtained by twin-screw extrusion granulation and single screw extrusion calendering.After the mechanical properties of each formula were tested,the tensile strength of the composites was obtained by orthogonal analysis.The optimum ratio was HDPE/PA6/HDPE-g-MAH=60/20/20.The formula and process were adjusted,and the roll speed of the calender was adjusted under the fixed single screw temperature and speed.It was found that the comprehensive performance of the composite was the best when the calendering rate was 16 rpm.Later experiments were carried out on this basis.Then,ultra-high density polyethylene,nano-Si O2and PA nanofiber nucleating agent were added in one-step method to blend with the composites directly and process them into the required experimental samples.After the study,it was found that adding a small amount of ultra-high density polyethylene can improve the crystallinity of the composite,increase the Vicat softening point by 2.2℃.With the increase of content,the impact strength is nearly twice higher than that of pure HDPE,and the tensile strength of the welding joint is increased by 98.6%,but the tensile properties and elongation at break of the material are reduced.The addition of nano-Si O2and PA nano fiber nucleating agent reduced the tensile strength and increased the elongation at break of the composite.When the content of nano-Si O2was 4 phr,it was 725.4%,and when the content of nucleating agent was 0.9 phr,it was 776.4%,which exceeded that of pure HDPE and improved the toughness of the composite.Both of them have no significant effect on the Vicat softening point of the composites,but the tensile strength of the welded joint is greatly improved.Then,through two-step method,PA6 was modified with organic montmorillonite（OMMT）.It was found that when the content of OMMT was 3 phr,the comprehensive performance was the best,and the tensile strength reached the highest of 82 MPa.OMMT existed in PA6 in partial peeling state,which could induce the formation of PA6γCrystal form,which plays the role of heterogeneous nucleation.On this basis,after adding PA nano nucleating agent,the tensile strength is the highest when the content of nucleating agent is0.9 phr,which is 17.4%higher than that of pure PA6,and the impact strength is 26.5%higher than that of pure PA6 when the content of nucleating agent is 0.5 phr.The crystallinity of the composite increases with the content of nucleating agent.When PA6/OMMT/nucleating agent（100/3/0.5）,the comprehensive performance is the best.The study of modified PA6,HDPE and HDPE-g-MAH under different processing temperature and calendering rate shows that the tensile strength of the composite increases significantly at lower processing temperature.With the increase of calendering rate,it can induce molecular chain orientation,improve PA6 crystallinity,improve the mechanical properties of the composite in orientation,and gradually increase the tensile strength of the welding joint. |
