Abstract Lap joints were prepared by gluing spruce plates with three types of adhesives (phenol-resorcinol-formaldehyde, PRF; one-component polyurethane, PUR; and epoxy, EP). The joints were exposed to 140 °C and 170 °C for 24 h (20, 40, 60, 80, 180 and 1140 min) and then loaded in four-point bending to verify the behavior of glued lap joints in building structures exposed to fire in its initial stage and stressed in transverse direction. The lap joint strength was compared to that of spruce specimens exposed to the same conditions and of the same stressed area. The failure mode of lap joints was evaluated visually; the failure mode was caused by exceeding the transverse load capacity of bulk wood. The strength of spruce fell by 40% after exposure to both temperatures for 20 min and next decrease began after 80-minute exposure at 170 °C as a result of the beginning of hemicellulose decomposition. Only PUR improved the spruce strength at 20 °C (by 30%) and at both temperatures except that after exposure to 170 °C for long time (3 and 24 h). The PUR-spruce lap joints revealed very good fire resistance for the initial fire exposure (80 min at 140 °C and 40 min at 170 °C). The strength of both PRF and EP lap joints was the same as that of spruce at 20 °C but PRF improved the spruce strength at 140 °C after 20-minute exposure (by 45%) and at 170 °C, where PRF lap joints bore the load irrespective of wood degradation. The EP lap joints revealed the worse thermal resistance due to rubber state of incompletely post-cured and degraded EP. To evaluate adhesive structure and its prospective change after thermal exposure and to evaluate the influence of adhesive thickness, the adhesives were cured in a form of bulk and thin films and tested by Thermogravimetry (TGA), Differential Scanning Calorimetry, Fourier Transformed Infrared Spectroscopy (FTIR) and evolved gas analysis (EVA) using TGA-FTIR. Curing and post-curing process was shown to be thickness dependent only in case of EP. Low-molecular components detected during adhesives heating were products of PUR and PRF post-curing and of unreacted hardnener decompositon in case of EP. All adhesives were degraded after thermal exposure to both elevated temperatures.

中文翻译：

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胶合云杉横向受力搭接接头的耐时温性能及胶粘剂热分析

摘要 通过用三种粘合剂（酚-间苯二酚-甲醛，PRF；单组分聚氨酯，PUR；和环氧树脂，EP）粘合云杉板制备搭接接头。将接头暴露在 140 °C 和 170 °C 下 24 小时（20、40、60、80、180 和 1140 分钟），然后进行四点弯曲加载，以验证暴露于高温下的建筑结构中胶合搭接接头的性能。火灾初期，横向受力。将搭接强度与暴露于相同条件和相同应力区域的云杉试样进行比较。搭接接头的失效模式通过目视评估；失效模式是由超过散装木材的横向承载能力引起的。在两种温度下暴露 20 分钟后，云杉的强度下降了 40%，而在 170°C 下暴露 80 分钟后，由于半纤维素开始分解，下一次强度开始下降。除了在 170°C 下长时间暴露（3 和 24 小时）之外，只有 PUR 提高了云杉强度在 20 °C（30%）和两种温度下的强度。PUR-云杉搭接接头在初始火灾暴露（140°C 下 80 分钟和 170°C 下 40 分钟）时显示出非常好的耐火性。PRF 和 EP 搭接接头的强度在 20 °C 时与云杉的强度相同，但 PRF 在 140 °C 暴露 20 分钟后（提高 45%）和 170 °C 时提高了云杉强度，其中 PRF 搭接接头无论木材降解情况如何，都可以承受负载。由于EP不完全后固化和降解的橡胶状态，EP搭接接头显示出较差的耐热性。为了评估热暴露后粘合剂的结构及其预期变化并评估粘合剂厚度的影响，将粘合剂以块状和薄膜形式固化，并通过热重法 (TGA)、差示扫描量热法、傅里叶变换红外光谱 (FTIR) 进行测试) 和逸出气体分析 (EVA)，使用 TGA-FTIR。仅在 EP 的情况下，固化和后固化过程才与厚度有关。在粘合剂加热过程中检测到的低分子成分是 PUR 和 PRF 后固化的产物以及在 EP 情况下未反应的硬化剂分解产物。所有粘合剂在热暴露于两种高温后都会降解。粘合剂以块状和薄膜的形式固化，并通过热重法 (TGA)、差示扫描量热法、傅里叶变换红外光谱 (FTIR) 和使用 TGA-FTIR 的逸出气体分析 (EVA) 进行测试。仅在 EP 的情况下，固化和后固化过程才与厚度有关。在粘合剂加热过程中检测到的低分子成分是 PUR 和 PRF 后固化的产物以及在 EP 情况下未反应的硬化剂分解产物。所有粘合剂在热暴露于两种高温后都会降解。粘合剂以块状和薄膜形式固化，并通过热重法 (TGA)、差示扫描量热法、傅里叶变换红外光谱 (FTIR) 和使用 TGA-FTIR 的逸出气体分析 (EVA) 进行测试。仅在 EP 的情况下，固化和后固化过程才与厚度有关。在粘合剂加热过程中检测到的低分子成分是 PUR 和 PRF 后固化的产物以及在 EP 情况下未反应的硬化剂分解产物。所有粘合剂在热暴露于两种高温后都会降解。在粘合剂加热过程中检测到的低分子成分是 PUR 和 PRF 后固化的产物以及在 EP 情况下未反应的硬化剂分解产物。所有粘合剂在热暴露于两种高温后都会降解。在粘合剂加热过程中检测到的低分子成分是 PUR 和 PRF 后固化的产物以及在 EP 情况下未反应的硬化剂分解产物。所有粘合剂在热暴露于两种高温后都会降解。