Modification Of Polypropylene-based Wood-plastic Composites By Using Inorganic Nano-fillers

With the continuous development of society,people pay more and more attention to green environmental protection,and wood-plastic composite materials are widely concerned by the society as a green environmental protection material.Wood-plastic composite material is a material made by mixing wood fiber,flax,sisal,agricultural and forestry waste and other plant fibers with polymer materials.It not only has the natural appearance of wood,but also has the ease of processing of polymer materials.The broad application prospects can replace the use of wood to a certain extent,and achieve the effect of saving forest resources and reducing costs.However,due to the introduction of a large number of plant fibers,wood-plastic composite materials also have some problems,such as poor melt flow,unstable melt flow,poor heat resistance,and poor flame retardancy.With the continuous development of nanotechnology,the application of nano-inorganic fillers is becoming more and more extensive.Nano-inorganic materials usually have the advantages of high hardness,strong heat resistance,and strong flame retardancy.Aiming at the problems of wood-plastic composite materials,the thesis uses nanoinorganic fillers to modify polypropylene-based wood-plastic composite materials,and systematically studies the relationship between material preparation,structure and performance.This paper first studied the effect of wood flour on polypropylene plastics,and found that with the increase of wood flour,the mechanical properties of polypropylene-based wood-plastic composites improved,but the melt flow rate and initial thermal decomposition temperature decreased.Using fumed silica and precipitated silica modified polypropylene-based woodplastic composites.Compared with precipitated silica,fumed silica has mechanical properties and Vicat on polypropylene-based wood-plastic composites.The increase in softening temperature is more obvious.The addition of silica will reduce the processing performance of the composite material,so the effects of three lubricants of PE wax,polyethylene glycol,and zinc stearate on the nano-silica filled wood-plastic composite materials were further studied.The results of the melt flow rate test found that PE wax has the best lubricant effect,followed by polyethylene glycol and zinc stearate.Capillary rheological test results show that the lubrication effect of each lubricant will change under different shear rates.Under high shear rate,zinc stearate has the best lubrication effect,followed by PE wax and polyethylene glycol.Rotational rheological test results found that zinc stearate has the best lubrication effect under the condition of small strain,followed by PE wax and polyethylene glycol.But under the condition of large strain,the lubricating effect of PE wax is better than zinc stearate.The addition of lubricant will cause the mechanical properties of the nano-silica filled wood-plastic composites to be reduced,of which the PE wax system has the smallest decrease,followed by polyethylene glycol and zinc stearate.Subsequently,in this paper,the method of preparing nano-silica by the sol-gel method and combining with the alkali treatment process were used to modify the wood flour in situ to prepare the wood flour / nano-silica hybrid.Scanning electron microscopy and Fourier infrared spectroscopy systematically studied the physical and chemical properties of the hybrid.The results of the study found that nano-silica was successfully generated in situ on the surface of wood flour,and the initial decomposition temperature of the hybrid was less modified.The wood flour has been increased by 11.9 ° C and the thermal stability of the wood flour has been improved.On this basis we further explored the application of hybrids in polypropylene-based wood-plastic composites.The results show that when the amount of nano-silica added is the same,wood-plastic composites prepared by in-situ modification have higher mechanical properties than wood-plastic composites prepared by directly adding nano-silica.When the amount of hybrid is 40wt%,the Vicat softening temperature of the composite material reaches 130.4 ?,which is 17.1 ? higher than the sample prepared by directly adding nano silica.When the amount of hybrid is 20wt%,the initial decomposition temperature of the composite is 380.9 ?,which is 34 ? higher than that of the sample prepared by directly adding nano silica.With the increase of the amount of hybrids,the oxidation induction period of the composite material showed an upward trend and then decreased.When the amount of hybrids was 20wt%,the oxidation induction period of the composite material reached 20.64 minutes.Observation through an electron scanning microscope revealed that wood-plastic composite materials prepared by directly adding nano-silica will show the phenomenon of wood flour shedding,while wood-plastic composite materials modified in situ with nano-silica have no obvious wood flour shedding The phenomenon shows that by in-situ preparation of nano-silica on the surface of wood flour,the combination of wood flour and matrix can be effectively improved.Finally,this paper uses alkali to treat the waste alkali produced by wood flour,and uses reverse drop method to generate nano-magnesium hydroxide in situ on the surface of wood flour to prepare wood flour / nano-magnesium hydroxide hybrid(MW).It is beneficial to improve the flame retardant performance of the composite material,and at the same time,it is also helpful to solve the problem of recycling the waste lye.The physical and chemical properties of wood flour / nano-magnesium hydroxide hybrids with different ratios of wood flour and nano-magnesium hydroxide were characterized by Fourier infrared spectroscopy,scanning electron microscope,X-ray diffraction,etc.The experimental results showed that magnesium hydroxide in wood The powder surface was successfully prepared in situ.And further systematically studied the application of wood flour / nano-magnesium hydroxide hybrid in polypropylene-based wood-plastic composites.The study found that as the ratio of magnesium hydroxide increases,the horizontal burning rate of the composite material decreases and the oxygen index increases.When the amount of hybrid is 20wt% and the ratio of wood flour to nano magnesium hydroxide reaches 1: 3,the composite The horizontal burning speed of the material reaches 17.89 mm / min,and the oxygen index reaches 18.9.With the increase of the amount of hybrid,the flame retardant performance of the composite material has been significantly improved.When the amount of the hybrid with the ratio of wood flour to nano magnesium hydroxide of 1: 1 reaches 50wt%,the horizontal burning rate of the composite material It fell to 4mm / min and the oxygen index reached 19.8.