Study Of Polyamide 12 Composites Applied To Selective Laser Sintering

Selective laser sintering(SLS)has attracted much attention because of its simple processing technology,high forming accuracy,large number of applied materials,and no structural restrictions on the structure of sintered components.At present,nylon 12(PA12)powder is the most widely used SLS forming material.In order to meet different performance requirements,a variety of micron inorganic filler modified PA12 composite powders have been developed,but these composites have a common shortcoming,its impact performance will be significantly lower,resulting in limited application scope.The study found that adding nano inorganic filler to a small amount of PA12 can not only improve the mechanical properties and thermal properties of the composites but also the impact of properties of materials.It has a good application prospect.The purpose of this paper is to prepare high toughness PA12 composites for SLS,and the performance of the composite powders are studied as well.Montmorillonite(MMT)is a common inorganic filler at present.After surfactant treatment,montmorillonite can be dissociated into nano flakes and dispersed in the polymer organic phase to form polymer composite materials.Cetyltrimethyl ammonium bromide(CTAB)and octedacy trimethyl ammonium bromide(OTAB)were used as organic intercalating cations to modify MMT.And the PA12/OMMT composites were prepared by the way of solution intercalation.The morphology of MMT and PA12/OMMT composites were characterized by XRD,FT-IR and SEM,the thermal stability of PA12/OMMT composites were characterized by TG,and their mechanical and thermal properties were also studied.The results show that when the treatment temperature was 80?,the surfactant was OTAB and its mass fraction was30% of the MMT,the MMT had the best modification effects,and the basal spacing of the MMT had increased from 1.24 nm to 2.13 nm,which indicated that the surfactant were successfully inserted into the nanostructure of the MMT.The OMMT were homogeneously dispersed in the PA12 matrix after organic modified,and the flowability and apparent density of the composite powder,the density and sphericity of the powder particles were much better than those of the pure PA12 powder,which improved the powder spreading efficiency and the forming precision of the sintered parts in the SLS process.The mechanical properties and thermal stability of thecomposite powder sample are obviously improved compared with the pure PA12 sample,especially the impact strength of the sample is increased by 34%.When the mass fraction of OMMT was 0.5%~1% of PA12,the comprehensive performances of PA12/OMMT were the best.Carbon nanotube(CNT)is a fibrous nanomaterial with excellent mechanical properties and thermal stability.It is a good composite material for polymer modification.However,CNT has a large specific surface area and is easy to agglomerate.Thus,CTAB,OTAB,sodium dodecyl benzene sulfonate(SDBS)and sodium dodecyl sulfate(SDS)were used to modify carbon nanotube(CNT)in different ultrasonic dispersion time.And PA12/CNT composites were prepared by the way of mechanical blending,and the properties of PA12/CNT composites were also studied.The results indicated that the CNT had the best dispersion effect when the SDBS has a mass fraction of 30% of the CNT in 4 hours.After the surface modification,the CNT were evenly adhered to pure PA12 powders with single form.And compared with pure PA12 powder,the flowability and apparent density of PA12/CNT composite powder have been greatly improved,which can improve the powder placement efficiency and sinter forming precision of composite powder in SLS process.And the mechanical properties and thermal properties of the composite powder sample have been greatly improved compared with the pure PA12 sample,especially the impact strength of the sample increased by 41%.When the mass fraction of CNT was 0.5%,the performances of PA12/CNT were the best.In conclusion,PA12/OMMT composite powder and PA12/CNT composite powder have high apparent densities,good sphericity of particles,and the composite materials have excellent mechanical and thermal performances,especially the impact toughness was improved significantly,provides two kinds of excellent properties of PA12 composite powder for SLS technology.