| The traditional hot waxed wood technology is a kind of wood surface coating technology with green environmental protection and excellent decorative effect,but the natural beeswax used has the disadvantages of low output,high cost,poor heat resistance and durability,low adhesion and easy to fall off,which can not completely meet hot waxing decoration quality and industrial needs of mass production.Replacing natural beeswax with polyethylene wax with a wide range of sources,low cost,non-toxic,high melting point and stable physical and chemical properties will be a new way to expand the application of hot waxing technology in the field of wood decoration and protection.However,there are still some problems in the use of polyethylene wax hot waxing,such as low adhesion and poor flexibility after film formation.The chemical modification of polyethylene wax is an effective way to solve the poor performance of hot waxing.Therefore,in order to obtain high quality polyethylene wax suitable for hot waxed wood,polyethylene wax was modified by grafting maleic anhydride-methyl methacrylate co-monomer.Modified polyethylene wax suitable for hot waxed wood process was prepared to replace beeswax.The optimized properties of modified polyethylene wax hot waxed wood were obtained by adjusting the hot waxing temperature and time.By adding oxidized paraffin and modified polyethylene wax,the hydrophobicity,wax layer adhesion,thermal stability and UV aging resistance of modified polyethylene wax hot waxed wood were further improved.The bonding mechanism of modified polyethylene wax and composite wax with wood surface and interface was revealed from the structure and characteristics of modified polyethylene wax and composite wax,the chemical composition of wood and the bonding characteristics of the interface between wax and wood.The main research contents and results of this paper are divided into the following five parts:(1)Polyethylene wax was modified by grafting maleic anhydride-methyl methacrylate co-monomer.The chemical properties,thermal properties,chemical structure and crystallization properties of the modified polyethylene wax were analyzed and compared with those of beeswax.The results show that the co-monomer grafting can effectively increase the acid value of polyethylene wax.Under the conditions that the mass ratio of the two monomers is 1/1,the total amount of monomer is 8 wt%of polyethylene wax,the amount of initiator is 2 wt%,and the reaction temperature is 150?,the acid value of modified polyethylene wax is consistent with that of beeswax and accords with the provisions of national standards,and the simulation of the main chemical properties of beeswax is realized.By comparing with the structure and properties of beeswax,it is found that the thermal stability and melting temperature of modified polyethylene wax are much better than that of beeswax,its crystal structure is similar to beeswax,and the cyclic anhydride and ester groups introduced by co-monomer grafting make polyethylene wax also have polar groups.(2)Based on the study of the surface and interface properties of modified polyethylene wax hot waxed wood under different hot waxing temperature and time,an optimized properties of hot waxed wood was proposed and the bonding mechanism between wax and wood surface and interface was revealed.The results showed that the modified polyethylene wax was successfully filled in the wood cell lumina and cross-linked with the wood matrix by esterification of the grafted anhydride group with hemicellulose or lignin hydroxyl groups in the wood cell wall.When the hot waxing temperature is 180? and the hot waxing time is 40 min,the modified polyethylene hot waxed wood shows the best surface properties.Its surface water contact angle and water uptake after immersion for 192 h are similar to those of beeswax hot waxed wood.Compared with beeswax hot waxed wood,its surface roughness(Ra)and maximum thermal weight loss rate are reduced by 84%and 24%,respectively,and its surface gloss and adhesion of wax layer are increased by nearly 5 times and 4 times respectively.Modified polyethylene wax can replace beeswax in the process of hot waxed wood.(3)The changes of color,gloss,water uptake,contact angle,adhesion of wax layer and surface morphology and chemical changes of beeswax and modified polyethylene wax hot waxed wood during UV accelerated aging were tested.The aging mechanism of beeswax and modified polyethylene wax and their effects on the resistance to UV-induced oxidative degradation of wood were analyzed.The results showed that after aging for 480 h,the total color difference and gloss loss rate of modified polyethylene wax hot waxed wood decreased by 58%and 73%respectively compared with untreated wood,and decreased by 51%and 60%compared with beeswax hot waxed wood,respectively.The reduction of wax layer adhesion and surface contact angle was 26%and 9%respectively,which was lower than 77%and 21%of beeswax hot waxed wood.The water uptake after aging was 37.1%,which was lower than 45.3%of beeswax hot waxed wood.The improvement of wood surface discoloration and gloss loss by modified polyethylene wax hot waxing is better than beeswax.Modified polyethylene wax hot waxed wood basically maintains its hydrophobicity and wax layer adhesion after aging.Through the comparative analysis of the surface micro-morphology and chemical changes,it was found that the UV-induced oxidation resistance of the wax layer of the modified polyethylene wax is stronger than that of the beeswax,and it has a better protective effect on the photodegradation of wood exposed for a long time.(4)In order to further improve the hydrophobicity,wax layer adhesion and thermal stability of modified polyethylene wax hot waxed wood,the composite wax hot waxed wood test was carried out by adding oxidized paraffin and modified polyethylene wax.The effects of the addition of oxidized paraffin on the properties of hot waxed wood and the bonding mechanism between wax and wood surface and interface were analyzed by studying the surface and interface properties of composite wax hot waxed wood with different amount of oxidized paraffin.The results show that the addition of oxidized paraffin improves the penetration of modified polyethylene wax into wood,promotes the infiltration of wax to the micro-pores on the wood surface and the filling in the cell lumina,and makes the distribution of wax deposited in the cell lumina more uniform.In addition,the addition of oxidized paraffin can not only improve the reaction probability between modified polyethylene wax and wood hydroxyl group,but also inhibit the thermal decomposition of modified polyethylene wax and improve the thermal stability of wood.When the mass ratio of modified polyethylene wax to oxidized paraffin was 70/30,the composite wax hot waxed wood showed the best surface properties,and its water uptake after immersion for 192 h was 10%lower than that of modified polyethylene wax hot waxed wood.Compared with the modified polyethylene wax hot waxed wood,the surface water contact angle and wax layer adhesion increased by 13%and 32%,respectively.(5)The changes of color,gloss,water uptake,contact angle,adhesion of wax layer and surface morphology and chemical changes of modified polyethylene wax and its oxidized paraffin composite wax hot waxed wood during UV accelerated aging were tested.The aging mechanism of the wax layer of modified polyethylene wax and composite wax and its effect on the resistance to UV-induced oxidative degradation of wood were analyzed.The results showed that after aging for 480 h,the total color difference and gloss loss rate of composite wax hot waxed wood decreased by 76%and 88%respectively compared with untreated wood,and decreased by 43%and 57%respectively compared with modified polyethylene wax hot waxed wood.The reduction of wax layer adhesion and surface contact angle was 13%and 5%respectively,which was lower than that 26%and 9%of modified polyethylene wax.The water uptake after aging reached 25.6%,which was lower than 37.1%of modified polyethylene wax.The improvement of discoloration and gloss loss of wood surface by composite wax hot waxing is better than that of modified polyethylene wax.The change of wax layer adhesion caused by aging is further reduced by the use of composite wax hot waxing,and the composite wax hot waxed wood still maintains higher surface contact angle and lower moisture content after aging.Through comparative analysis of surface micro-morphology and chemical changes,it was found that the addition of oxidized paraffin enhanced the ability of modified polyethylene wax to resist UV oxidative degradation,reduced the UV radiation penetration,and had a better protective effect on the photodegradation of lignin.The composite wax hot waxed wood showed long-term photostability after aging. |
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