Research paperPreparation of Ureido-palygorskite and its effect on the properties of urea-formaldehyde resin
Introduction
Urea-formaldehyde (UF) resins are the most widely used adhesive which have been applied in plywood, particleboard, medium density fiberboard (MDF), oriented strand board (OSB) and other artificial boards due to their low cost, moderate cure temperature and other advantages (Akyüz et al., 2010, Boran et al., 2011). However, hydrophilic groups such as hydroxyl, amino and amide exist in the molecular chain of UF with a large emission of free formaldehyde leading to the poor water-resistance performance of UF (Dunky, 1998, Roumeli et al., 2012, Tong et al., 2010). On most cases, the adhesion strength is not satisfactory compared to the other adhesives used for lumbering. All these disadvantages seriously restrict the applications of UF.
Recently, inorganic nanomaterials have been widely used to prove the adhesive performance. Modification of adhesive plays an important role in enhancing its performances. Natural palygorskite clay is a silicate mineral that contains 70 to 80% palygorskite (PA); 10 to 15% montmorillonite, sepiolite and other clays; 4 to 8% quartz; and 1 to 5% calcite and dolomite (Haden and Schwint, 1967). Due to its various structures, such as fiber, rod-like and porous crystal structures, palygorskite has been extensively studied (Fan et al., 2009, Khorami and Nadeau, 1986, Pan and Chen, 2007). It has a channel of about 0.37 nm × 0.64 nm of cross section with reactive ―OH groups on its surface, and has excellent ion exchange capacity, which make PA widely investigated as an adsorbent for the removal of organic contaminants (Frost and Ding, 2003, Xue et al., 2010, Zhang and Wang, 2010). The diameter of a single-crystal is just dozens of nanometers, and the length may reach micron scale. The high aspect ratio of PA fiber makes it used in the reinforcement of polymer matrix including rubber, polyurethane, epoxy resins, etc. (Lan and Pinnavaia, 1994, Tian et al., 2003, Xu et al., 2009). Thus, PA shows preferable adsorptive capacity and exceptional reinforcing performance because of its unique crystal structure.
In this paper, we took full advantage of the porosity of palygorskite for the formaldehyde adsorption and its special one-dimension characteristic for the reinforcement, whose structure is largely different from the other clays such as kaolin, montmorillonite, halloysite and so on. γ-Ureidopropyltriethoxysilane (UPTES) containing ureido groups (NH2―OC―NH―) is a feasible modifier in the treatment of UF, and it is easy to be linked to UF resins since its functional group is similar to urea. Also, UPTES can be used for surface modification of PA by chemical or physical reaction and the combined capability of organo-PA and UF would be better than the individual component, which might improve effectively the whole performance of the composites. This work would set a positive example to PA applied in other polymers.
Section snippets
Materials and reagents
PA (purity 99%, grain size 100 mesh), whose aspect ratio is beyond 10, was supplied by Jiangsu NDZ Technology Group Co., Ltd. It has the following chemical composition (wt.%): 1.45% Na2O, 1.21% CaO, 10.50% Al2O3, 20.40% MgO, 64.39% SiO2, 0.12% K2O and 0.93% Fe2O3 as determined by X-ray fluorescence. The BET surface area is 132.75 m2/g, the BJH average pore volume is 0.44 cm3/g and the average pore diameter is 19.50 nm as determined by N2 adsorption–desorption experiment. UPTES was provided by
FTIR analysis
Structure changes of PA before and after modification were studied by FTIR spectra (Fig. 1). Compared to curve 1, two new peaks at 1568 cm− 1 and 1446 cm− 1 were observed on curve 2. The peak at 1568 cm− 1 is attributed to bending vibration of the N―H bonds existing in imino groups of UPTES and the peak at 1446 cm− 1 is assigned to the C―N stretching vibration (Wang et al., 2009, Yang and Liu, 2009). It also could be seen that the intensity of peaks at ~ 2930 cm− 1 and 800 cm− 1 in curve 2 increased
Conclusion
In this work, the results of FTIR, XPS, and TG-DTA confirmed that UPTES was grafted onto the surface of PA by chemical bonding successfully. Compared with the PA/UF composites, Ureido-PA/UF composites had the better waster-resistance and the higher thermal stability and it was found that Ureido-PA could increase the shear strength and decrease the free formaldehyde content of UF resins considerably. The porosity of palygorskite for the formaldehyde adsorption and its special one-dimension
Acknowledgments
This work was supported by the Natural Science Foundation of China (51002016), Technology Innovation Team of Colleges and Universities Funded Project of Jiangsu Province (2011-24), the Priority Academic Program Development of Jiangsu Higher Education Institutions (PAPD), Research and Innovation Plan Project for College Graduates of Jiangsu Province (CXZZ12_0185), Technology Support Plan of Jiangsu Province (BE2011125), Jiangsu Key Laboratory of Environmental Material and Environmental
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