Luo Bin, Jia Zhuan, Jiang Hongrui, Wang Shuangfei, Min Douyong
College of Light Industry and Food Engineering, Guangxi University, Nanning 530004, China.
Guangxi Key Laboratory of Clean Pulp & Papermaking and Pollution Control, Guangxi University, Nanning 530004, China.
Polymers (Basel). 2020 Aug 14;12(8):1825. doi: 10.3390/polym12081825.
The low reactivity of lignin hinders its application as a phenol substitute in phenol-formaldehyde (PF) resin. Therefore, the combination of fractionation and phenolation was adopted to enhance the reactivity of lignin for preparing a phenol-formaldehyde resin adhesive. Sugarcane bagasse kraft lignin and its fractions were employed to replace 40 wt% of phenol to prepare a PF adhesive. The fractionation increased the reactivity of lignin, however the as-prepared lignin-based PF (LPF) hardly met its application requirements as an adhesive. Therefore, the phenolation of lignin under an acidic condition was adopted to further improve its reactivity. The phenolated lignin was characterized by FTIR, gel permeation chromatography, and NMR, indicating its active sites increased while its molecular weight decreased. The phenolated lignin was used to replace 40 wt% of phenol to prepare a PF adhesive (PLPF) which was further employed to prepare plywood. The results indicated that the combination of fractionation and phenolation effectively enhanced the reactivity of lignin, and eventually improved the properties of the PLPF and its corresponding plywood. The free formaldehyde content of PLPF decreased to 0.16%. The wet bonding strength of the as-prepared plywood increased to 1.36 MPa, while the emission of formaldehyde decreased to 0.31 mL/L.
木质素的低反应活性阻碍了其作为酚醛（PF）树脂中酚类替代品的应用。因此，采用分级分离和酚化相结合的方法来提高木质素的反应活性，以制备酚醛树脂胶粘剂。采用甘蔗渣硫酸盐木质素及其馏分替代40 wt%的苯酚来制备PF胶粘剂。分级分离提高了木质素的反应活性，然而，所制备的木质素基PF（LPF）作为胶粘剂几乎无法满足其应用要求。因此，采用酸性条件下的木质素酚化来进一步提高其反应活性。通过傅里叶变换红外光谱（FTIR）、凝胶渗透色谱法和核磁共振（NMR）对酚化木质素进行了表征，结果表明其活性位点增加而分子量降低。用酚化木质素替代40 wt%的苯酚制备PF胶粘剂（PLPF），并进一步用于制备胶合板。结果表明，分级分离和酚化相结合有效地提高了木质素的反应活性，并最终改善了PLPF及其相应胶合板的性能。PLPF的游离甲醛含量降至0.16%。所制备胶合板的湿胶合强度提高到1.36 MPa，同时甲醛释放量降至0.31 mL/L。
