改性脲醛树脂粘合基质块性能及其对黄瓜幼苗生长的影响

针对机械化移栽过程中,基质容易散落,造成根系损伤的问题,该研究采用了既具有粘合性又具有养分释放功能的生物降解胶黏剂粘合基质成块。测定了水解蛋白改性脲醛树脂的基本性能,基质块的孔隙度、EC值、pH值和抗压强度的变化规律,以及基质块对黄瓜幼苗生长的影响。试验结果表明,该改性脲醛树脂的氮素释放速率前期缓慢,后期较快,在第7周时养分释放率可达48%。添加50%改性脲醛树脂后,基质块的总孔隙度下降约8.4%,但还是能够满足黄瓜生长需要。然而添加改性脲醛树脂后基质块的EC由2.51 mS/cm下降到1 mS/cm左右,pH值基本保持不变。改性脲醛树脂在添加量50%时,抗压强度为0.14 MPa以上,能够满足机械手抓取的要求,也能够满足幼苗根系生长的要求。同时,叶面积、鲜质量、干质量比普通基质提高了89.86%、57.00%、79.2%。III-UF改性脲醛树脂的养分释放速率与黄瓜幼苗生长养分需求速率是一致的,该配方最有利于黄瓜幼苗的生长。添加胶黏剂后,每个颗苗只需增加0.0125元,从成本上看价格便宜,有利于推广应用。

Performance of substrate blocks glued by modified urea formaldehyde resins and its effect on cucumber seedlings

Abstract: In order to solve the problem of scattering substrates and the damaged root during the process of mechanized transplanting, the hydrolyzed soy protein modified urea formaldehyde resins were applied to glue the substrates together. The properties of modified resins, such as pH value, viscosity, solid content, density, curing time, and free formaldehyde, were characterized. The nutrient release rate of modified urea formaldehyde resins was characterized. The aeration porosity, water-holding porosity, EC, pH value, and compressive strength of the substrate blocks were also tested; the effect of the substrate block on the cucumber seedling was measured. The results show that the hydrolyzed soy protein modified urea formaldehyde resins can meet requirements of gluing the substrates together. The viscosity and curing time increase obviously. And, the solid content and free formaldehyde decrease a little. The reason is that the viscosity of hydrolyzed soy protein is higher than urea formaldehyde resins, and the solid content is lower than urea formaldehyde resins. The active groups in modified urea formaldehyde resins are fewer than unmodified urea formaldehyde resins. In addition, the space barrier from the soy protein causes the increased curing time, because the hydroxymethyl groups formed from active amino groups of hydrolyzed soy protein and formaldehyde are more stable than that formed from urea and formaldehyde. The nutrient release rate is an important indicator of the substrate block. Soil column leaching method was applied to characterize the nitrogen release rate. The nitrogen release rate in the first 3 weeks is slower. Then the nitrogen release rate is improved in the later time, and the release rate can reach 48% in the 7th week. The reason is the specific surface area increases as the time goes on. The aeration porosity, water-holding porosity, and total porosity of the substrate blocks are decreased by 6.6%, 9.0%, and 8.4% compared with the traditional substrate. The reason is that the porosity and the hydrophilic groups of the substrate are covered by modified urea formaldehyde resins. However, the porosity can meet the growth requirement of the cucumber seedling when the modified urea formaldehyde resins are added in the substrates in the proportion of 1:2. The EC of substrate block decreases from 2.5 to 1 mS/cm. The pH value of the substrate block remains unchanged. The compress strength of the substrate block is above 0.14 MPa, which can meet the requirement of grabbing of manipulator during the transplanting process. When the modified urea formaldehyde is added, the height, stem diameter, root length are improved by 27.81%, 15.40%, and 18.10%, respectively. And the leaf area, fresh and dry weight are improved by 89.86%, 57.00%, and 79.2%, respectively. In addition, the substrate blocks with 50% resins are suitable for the root growth of cucumber seedlings. III-H-UF is the best resins that the nutrient release rate is in accordance with the nutrient requirement characteristics of the cucumber seedlings. The formula of the substrate blocks is suitable for the cucumber seedlings growth. Every seedling tray increases by 0.9 yuan when blended with modified urea formaldehyde resins. And every seedling increases by 0.0125 yuan for seedling tray with 72 holes.