| In this research,to explore the modification mechanism and curing process of the UPR in Chinese Fir,the Chinese Fir impregnated with UPR was prepared to analyze properties such as mechanical properties and dimensional stability.And the modification mechanism,curing kinetics and curing reaction were researched systematically.This paper could broaden the efficient utilization of the fast-growing wood and enrich the basic theory of the impregnation modification of UPR.The main results of this paper was listed below:(1)The vacuum impregnation method was used to impregnated the Chinese Fir with UPR.The results indicated that,the effect of the vacuum degree to the curing weight percent gain was evident,while the vacuum duration was not.The optimal modification process of Chinese Fir,according to the curing weight percent gain and the quality of the modified wood after curing,was impregnated at-0.08 MPa vacuum for 30 min,120 min at atmospheric pressure with submersion in the modifier,and post-processing under a-0.09 MPa vacuum for 30 min without the modifier.(2)The modification mechanism of the UPR to the Chinese Fir was that UPR was closely adhereing to the surface of the cell cavity.And it was a kind of chemical bonding,then the mechanical properties and dimensional stability of the Chinese Fir impregnated with UPR was significantly enhanced than Chinese Fir itself.The results indicated that,the bending strength of the wood impregnated with and without post-processing was improved 71.65%and 112.85%,respectively,and the modulus of elasticity improved 58.28%and 67.13%,respectively.The average hardness of the modified wood was improved 14.22%.The dimensional stability of moisture and water absorption was both improved by unsaturated polyester resin impregnation,and the volume swelling ratio and water absorption was reduced obviously.The cell wall of the modified wood was more even than the untreated wood,and the thickness of the cell wall of the Chinese Fir,UPR-impregnated Chinese Fir with and without post-vacuum was 2.9 ?m,8.19 ?m,and 8.97 ?m,respectively.The hydroxyl group of the modified wood was decreased than the untreated wood,while the ester group was increased.(3)The curing kinetics and curing reaction of the UPR and UPR-impregnated Chinese Fir was analyzed for the curing process,pre-exponential factor,curing reaction order and curing dynamic equation.The results indicated that the apparent activation energy of UPR was 150.167 kJ/mol,the average pre-exponential factor was 1.07×1020.Although the the apparent activation energy of the UPR-impregnated Chinese Fir was lower than the UPR itself,the curing reaction temperature was higher than UPR.(4)The composition of gaseous production and the functional changes of the solid product was analyzed.The results indicated that,the gaseous production of the UPR during curing process was styrene and water,while the gaseous production Chinese Fir and modified wood was water only.The reaction during the curing of the modified wood was not only polymerization but also the reaction with the-OH of wood at the temperature of 50?-90?.(5)The heat transfer process of the UPR-impregnated Chinese Fir was analyzed and the transverse thermal coefficient of the modified Chinese Fir related to the volume fraction of UPR and porosity the modified wood was concluded.The results indicated that,the distribution of temperature of the modified wood was more even than the Chinese Fir at various environment temperature.The curing reaction was initiated at the temperature of 84.2?.The transverse thermal coefficient of the samples in this research was 2.79×104 cal/(cm ·?·s). |
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