Study On The Bonding Properties Of Larch,Birch And Oak

Bonding properties of Larch , Birch and Oak with aqueous polymer isocyanate adhesives were studied in this paper. First, effects of grain orientation of Larch s Birch and Oak on bonding properties were studied in this paper. The results showed that: dry compressing shear strength of quarter-sawn board of Larch was 1.41 times of flat-sawn board of Larch in normal conditions; wet compressing shear strength of quarter-sawn board of Larch was 0.29 times of flat-sawn board of Larch for repeatedly boiling samples. While dry compressing shear strength of quarter-sawn board of Birch was 0.91 times of flat-sawn board of Birch in normal conditions; wet compressing shear strength of quarter-sawn board of Birch was 1.23 times of flat-sawn board of Birch for repeatedly boiling samples. While dry compressing shear strength of quarter-sawn board of Oak was 1.22 times of flat-sawn board of Oak in normal conditions; wet compressing shear strength between quarter-sawn board and flat-sawn board of Oak for repeatedly boiling samples had no difference.The reasons that cause those phenomena were also analysised in this paper. The main reason why quarter-sawn board of Larch had greater dry compressing shear strength than flat-sawn board of Larch in normal conditions was great difference between springwood and summerwood of Larch. The reasons why quarter-sawn board of Larch had smaller wet compressing shear strength than flat-sawn board of Larch for repeatedly boiling samples were as follows: first of all, antiswelling efficiency between springwood and summerwood of Larch was different; secondly, pits of Larch had great effect on this aspect. The main reason why quarter-sawn board of Birch had smaller dry compressing shear strength than flat-sawn board of Birch in normal conditions was that Birch had different shear strength to the grain between quarter-sawn board and flat-sawn board. Meanwhile xylary rays in flat-sawn board were transversely cut and left a lot of pores in the flat-sawn board, so adhesive can enter these pores and turn into adhesive nail. While these pores provided a kind of tunnel for water, so cause this phenomenon that wet compressing shear strength of flat-sawn board of Birch was smaller than that of quarter-sawn board of Birch. The possible reason why quarter-sawn board of Oak had greater dry compressing shear strength than flat-sawn board of Oak in normal conditions was that ratio of springwood on quarter-sawn board and flat-sawn board was different. Because the strength of springwood was very low, the strength of board which included more springwood was low. The main reason why there was no difference in wet compressing shear strength between quarter-sawn board and flat-sawn board was that quarter-sawn board had a lot of pits on radial cell wall and in flat-sawn board xylary rays were transversely cut and left a lot of pores which provided a kind of tunnels for water.Secondly, comparison of bonding properties of Larch , Birch and Oak was studied. The results showed that : the dry compressing shear strength of Oak in normal conditions wasthe greatest ; the dry compressing shear strength of Birch in normal conditions was the second. The dry compressing shear strength of Larch in normal conditions was the lowest. The factors (such as wettability, roughness, surface chemical composition) affecting their bonding properties were researched.Thirdly, surface treatment of Larch was studied. The results showed that: the dry compressing shear strength of Larch treated with H2O2 solution was raised by 15%, FTIR results showed that carbonyl of Larch treated with H2O2 increased. Wettability of Larch treated with H2O2 solution was better than untreated wood by measuring surface contact angle.Last ,adhesive theories between wood and aqueous polymer isocyanate adhesives for wood were studied.There was chemical reaction between API adhesive and wood by FTIR and ESCA. The results of DSC showed that: the reactive energy between API adhesive and wood was greater than main agent and curing agent of API adhesive.