Abstract This paper presents a study of two crucial synthesis parameters of the alkaline-acid process of UF resin synthesis: condensation formaldehyde/urea (F/U) molar ratio and U feed rate during the methylolation step. The differences in the polymeric structures and the performance of the ensuing resins on particleboards (PBs) properties were analyzed and compared with a standard resin. The molecular weight distribution of the resins was monitored by gel permeation chromatography/size exclusion chromatography (GPC/SEC) and the unreacted oligomers by high-performance liquid chromatography (HPLC). The PBs produced were analyzed following European standards for mechanical tests and formaldehyde emission. The data obtained were also submitted to a statistical analysis. The results obtained showed that the use of low molar ratios yield higher internal bond strength (IB) values and lower formaldehyde emissions (F). In turn, the effect of urea feed rate during the methylolation step on IB values depends on the F/UII molar ratio used: (i) a reduction for the higher final molar ratio used, and no effect for the lowest final molar ratio used. Moreover, the statistical analysis carried out showed that F/UII molar ratio has significance on almost all of the resins’ characteristics. The resin used as standard yielded the best results when the final F/U molar ratio was 1.10 and the resulting PBs presented values of internal bond (IB) of 0.51 N mm−2 and formaldehyde content (F) of 5.1 mg/100 g o.d.b., complying with the market requirements. Additionally, the effect of resin ageing was also studied and the PBs prepared using the best resin upon fifteen days of its production presented similar IB values and even lower F content in relation to those obtained using fresh resin.

中文翻译：

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碱-酸法合成脲醛树脂的合成参数研究

摘要 本文研究了 UF 树脂合成的碱酸工艺的两个关键合成参数：缩合甲醛/尿素 (F/U) 摩尔比和羟甲基化步骤中的 U 进料速率。分析了聚合物结构的差异以及随后的树脂在刨花板 (PB) 上的性能，并与标准树脂进行了比较。树脂的分子量分布由凝胶渗透色谱/尺寸排阻色谱 (GPC/SEC) 监测，未反应的低聚物由高效液相色谱 (HPLC) 监测。按照欧洲机械测试和甲醛释放标准对生产的 PB 进行分析。获得的数据也提交给统计分析。获得的结果表明，使用低摩尔比会产生更高的内键强度 (IB) 值和更低的甲醛释放量 (F)。反过来，羟甲基化步骤期间尿素进料速率对 IB 值的影响取决于所使用的 F/UII 摩尔比：(i) 所使用的较高最终摩尔比的减少，并且所使用的最低最终摩尔比没有影响。此外，进行的统计分析表明，F/UII 摩尔比对几乎所有树脂的特性都具有重要意义。当最终 F/U 摩尔比为 1.10 且所得 PB 的内键 (IB) 值为 0.51 N mm-2 和甲醛含量 (F) 为 5.1 mg/100 g odb 时，用作标准的树脂产生最佳结果，符合市场要求。此外，