摘要
研究了压缩和热处理因素对密实化杨木单板的密度、尺寸稳定性的影响。研究结果表明:压缩前单板含水率应低于15%,随着压缩压力的增大和温度的升高,单板的密度逐渐增大,与未处理单板相比,压力为10 MPa时,压缩单板的密度增幅达98.8%,压缩温度140℃时密度增加了81.4%,加压时间对密度有较显著影响,在加压时间8 min时密度达0.748 g.cm-3,但随着时间的增加,热解使压缩单板密度有所降低;各压缩因素对20℃条件下的厚度回弹率和70℃水煮回弹率的影响趋势一致,且回弹率均高于50%,杨木单板最佳的压缩工艺参数为初含水率≤15%,压缩压力8 MPa,温度140℃,时间8 min。热处理使木材中纤维素、半纤维素、木素等成分也发生了化学变化,使吸湿性最强的半纤维素热解,含量下降,吸水性羟基数量减少,表现在经热处理后的压缩单板,回弹率明显低于压缩杨木单板,但随着热处理温度的升高和时间的延长,压缩杨木单板失重率逐步增加,密度呈下降趋势。为保持压缩单板的密度,热处理温度和时间分别不宜超过210℃和40 min。
The influence of compression and heat-treatment on density and dimensional stability of densified poplar veneer was studied.By changing the elements of hot-pressing and heat-treatment,such as the initial moisture content,compression pressure,temperature and time,heat-treatment temperature and time,the properties of poplar had significant improvement.Results indicated that the initial moisture content should be below 15%.As compression pressure and temperature increased,density continuously improved.When pressure reached 10 MPa,the density was 98.8% higher than untreated veneer,and it was 81.4% higher as the compression temperature rose to 140 ℃.Hot-pressing time showed a density increase of 0.748 g·cm-3 for 8 min.Pressed veneer in 20 ℃ and 70 ℃ water had a recovery of set of over 50%.Optimal treatment parameters for densified poplar veneer were initial moisture content under 15%,pressing temperature of 140 ℃,pressing pressure of 8 MPa,and time of 8 min.Chemical component analysis showed that cellulose,hemicellulose and lignin changed with heat-treatment,especially the content of hemicelluloses decreased,and degradation of the strongest hygroscopicity of hemicellulose led to a reduction of hydroscopicity hydroxyl.With higher temperatures and longer times,the weight-loss ratio gradually increased and density decreased.Thus,to maintain density,the temperature should be below 210 ℃,and the time should be less than 40 min
出处
《浙江农林大学学报》
CAS
CSCD
北大核心
2013年第4期536-542,共7页
Journal of Zhejiang A&F University
基金
江苏省科技厅富民强县项目(BN2009220)
关键词
林业工程
杨木单板
压缩
热处理
密度
回弹率
forest engineering
poplar veneer
compression
heat-treatment
density
recovery of set
