Research On Preparation And Properties Of Laser Marking Polypropylene Composite Materials Based On Molybdenum Sulfide

Laser marking technology is widely used in text symbol marking and patterning modification on the surface of materials because of its fast,efficient,durable marking,and environmental friendliness.Polypropylene（PP）has a large output and a wide range of applications,but it is difficult to absorb near-infrared laser energy with a wavelength of 1064 nm,and it is almost difficult to produce carbonized and blackened markings.In order to improve the laser marking performance of PP materials,firstly,molybdenum disulfide（MoS₂）is selected as the laser-sensitive additive,and directly introduced into PP through a simple melt blending method to prepare PP/MoS₂ composites;Secondly,in order to improve the particle dispersibility of MoS₂ and its compatibility with the PP matrix,and to improve the laser-induced carbonization of the PP surface,and using free radical polymerization,a layer of easily carbonized polystyrene（PS）was grafted onto the surface of the MoS₂ particles to obtain the modified MoS₂-g-PS laser sensitive particles,and PP/MoS₂-g-PS composites are also prepared by melt blending;Finally,in order to overcome the low utilization rate and high cost problems of the traditional method of filling laser sensitive particles,the electrostatic force driven layer-by-layer（Lb L）self-assembly technology was used to build a multilayer composite film of polyethyleneimine（PEI）and MoS₂ on the surface of PP.The Lb L process is simple and the film thickness is adjustable.The PP/PEI/MoS₂composite material was prepared.The prepared three PP composite materials was laser marked using a semiconductor laser with a wavelength of 1064 nm,and characterized using metallographic microscope,optical microscope,scanning electron microscope（SEM）,transmission electron microscope（TEM）,color difference meter,X-ray photoelectron spectroscopy（XPS）),Fourier Transform Infrared Spectroscopy（FT-IR）,Raman Spectroscopy（Raman）,Thermogravimetric Analyzer（TGA）,X-ray Diffraction（XRD）.The surface morphology,structure,and composition of PP composite materials before and after laser marking was analyzed,and the marking performance of PP composite material（blackness,edge definition,color difference value,surface roughness,etc.）,the optimum addition amount,the best laser process parameters and the mechanism of laser marking discoloration were investigated.This work will provide a reference for the high-definition and contrast laser marking,anti-counterfeiting identification,and pattern modification applications of polyolefin materials.The main contents include:1.The PP/MoS₂ composite was prepared by introducing MoS₂ directly into PP through a simple melt blending method,and the influence of the amount of MoS₂,laser current intensity,laser scanning speed,and other process parameters on the marking performance of the composite was studied.The results show that the addition of MoS₂ enables the laser marking of PP materials under the laser irradiation at the wavelength of1064 nm.When the loading content of MoS₂ is 0.02 wt%,the laser marking current intensity is 11 A,and the laser marking scanning speed is800 mm/s,PP/MoS₂ composite material has the best laser marking performance;when the content of MoS₂ in the composite material system is 0.2 wt%or the laser marking current is 12 A,the surface of the material was severely ablated by the laser,or even bubbling,which affects the marking performance of PP composites.The main reason for the discoloration of PP/MoS₂ composite laser marking is that the MoS₂laser-sensitive particles can effectively absorb laser energy,causing local overheating of PP chains around the particles,making the PP composite pyrolyzed to generate amorphous carbon,thereby forming black markings.2.The modified laser-sensitive particles MoS₂-g-PS were introduced into PP by means of melt blending to prepare PP/MoS₂-g-PS composites.Compared with PP/MoS₂,the laser marking property of PP/MoS₂-g-PS composite material was improved.When the content of MoS₂-g-PS is 0.02wt%,the two-dimensional code pattern obtained by laser marking can be easily recognized,and the laser marking pattern has high definition.Because MoS₂ can effectively absorb near-infrared laser energy to produce photothermal conversion,while the PS layer coated on the surface of MoS₂ particles absorbs laser energy to form carbonized materials by itself.The synergic effect caused by the two components leads to a higher degree of carbonization and definition of laser markings.The introduction of laser-sensitive particles MoS₂-g-PS can effectively improve the laser marking performance of PP.A layer of PS on the surface of MoS₂ can effectively improve the compatibility of the laser-sensitive inorganic particles MoS₂-g-PS with the PP matrix.Compared with the PP/MoS₂ composite,the mechanical properties of the PP/MoS₂-g-PS composite were significantly improved.3.Using the Lb L self-assembly technology driven by electrostatic force,a multilayer film of polyethyleneimine（PEI）and MoS₂ was constructed on the surface of PP,and the PP/PEI/MoS₂ composite material was prepared,and its laser marking performance was investigated.The results show that:MoS₂ is uniformly distributed on the surface of PP material.When the layer number of the self-assembled multilayer composite films on the PP surface reaches 12,the laser marking pattern has a higher definition,compared with the traditional composite materials prepared by melt blending.The PP/PEI/MoS₂ composite material constructed by the Lb L self-assembly method has higher marking definition after laser marking.The PEI/MoS₂ multilayer film can effectively absorb laser energy and form a carbonized black marking.The degree of corrosion damage on PP surface after laser marking was small,and the mechanical properties of PP were maintained.