*Article* **Surfactant-Induced Reconfiguration of Urea-Formaldehyde Resins Enables Improved Surface Properties and Gluability of Bamboo**

**Lulu Liang, Yu Zheng, Yitian Wu, Jin Yang, Jiajie Wang, Yingjie Tao, Lanze Li, Chaoliang Ma, Yajun Pang \* , Hao Chen, Hongwei Yu \* and Zhehong Shen \***

> College of Chemistry and Materials Engineering, Zhejiang Provincial Collaborative Innovation Center for Bamboo Resources and High-Efficiency Utilization, National Engineering and Technology Research Center of Wood-Based Resources Comprehensive Utilization, Key Laboratory of Wood Science and Technology of Zhejiang Province, Zhejiang A&F University, Hangzhou 311300, China; m13070173339@163.com (L.L.); z541962382@icloud.com (Y.Z.); Y1tianWu@163.com (Y.W.); Yangjin\_0127@163.com (J.Y.); laowangwjj0126@163.com (J.W.); taoyingjie123@126.com (Y.T.); lilanze112@163.com (L.L.);

qq843543030@163.com (C.M.); haochen10@fudan.edu.cn (H.C.)

**\*** Correspondence: yjpang@zafu.edu.cn (Y.P.); yhw416@sina.com (H.Y.); zhehongshen@zafu.edu.cn (Z.S.); Tel.: +86-0571-6374-1609 (Y.P.)

**Abstract:** The high-efficiency development and utilization of bamboo resources can greatly alleviate the current shortage of wood and promote the neutralization of CO2. However, the wide application of bamboo-derived products is largely limited by their unideal surface properties with adhesive as well as poor gluability. Herein, a facile strategy using the surfactant-induced reconfiguration of urea-formaldehyde (UF) resins was proposed to enhance the interface with bamboo and significantly improve its gluability. Specifically, through the coupling of a variety of surfactants, the viscosity and surface tension of the UF resins were properly regulated. Therefore, the resultant surfactant reconfigured UF resin showed much-improved wettability and spreading performance to the surface of both bamboo green and bamboo yellow. Specifically, the contact angle (CA) values of the bamboo green and bamboo yellow decreased from 79.6◦ to 30.5◦ and from 57.5◦ to 28.2◦, respectively, with the corresponding resin spreading area increasing from 0.2 mm2 to 7.6 mm2 and from 0.1 mm2 to 5.6 mm2. Moreover, our reconfigured UF resin can reduce the amount of glue spread applied to bond the laminated commercial bamboo veneer products to 60 g m<sup>−</sup>2, while the products prepared by the initial UF resin are unable to meet the requirements of the test standard, suggesting that this facile method is an effective way to decrease the application of petroleum-based resins and production costs. More broadly, this surfactant reconfigured strategy can also be performed to regulate the wettability between UF resin and other materials (such as polypropylene board and tinplate), expanding the application fields of UF resin.

**Keywords:** surfactant; urea-formaldehyde resin; bamboo; laminated bamboo veneer; gluability
