Nanocomposites Bonded With Montmorillonite-modified Phenol-Formaldehyde Resin

Polymer/Montmorillonite (MMT) intercalation is one of the most widely studied and most promising nanocomposites. China is rich in Ca-MMT mineral. Due to its particular intercalation chemistry and nanoscale layering with very high aspect ratio, high strength, ion-exchangeable and swellable characteristics MMT plays an important role in producing high-performance intercalation nanocomposites. The intercalated nano-compounding of phenol formaldehyde resin with MMT is a creative thinking and practice, which has important scientific significance and attractive application prospects. The intercalated compounding with inorganic MMT at the molecular level is a pioneer concept to improve or modify phenol formaldehyde (PF) resin. In this research, the technology of compounding PF resin with MMT on a nanoscale and applying the modified resin to manufacture wood composites was systematically put forward. This exploring research would provide a new idea to modify PF resin in a new approach to prepare wood composites.MMT-modified PF resins suitable for use in bonding wood composites were prepared through in-situ intercalated polymerization and polymer intercalated polymerization using several montmorillonites. The PF resin molecules were first intercalated into the clay layers, followed by the formation of nanocomposites when the MMT-modified PF resin was cured under pressure at high temperatures. The work dealt with the use of different types and quantities of montmorillonite nanoclays in the preparation of thermosetting PF and PUF resins under different reaction conditions, such as different F/P mole ratios. It was hoped that the use of MMT in resin synthesis would improve the performance of MMT-modified the resins in manufacturing wood panels/composites. The MMT-modified resins were studied with the analyses of wide angle X-ray diffraction analysis (XRD), Matrix assisted laser desorption/ionization time of flight (MALDI-TOF-MS), differential scanning calorimetry (DSC) and thermomechanical analysis (TMA), obtaining the following results:1. MALDI-TOF spectra confirmed that the phenolic resins prepared in this study had a three-dimensional structure. The PF moieties made up the main part in the PUF resin, and the linkages also were of the PF types. Therefore, the performance of PUF resin was similar to the conventional phenolic resins. PF resins with different F/P mole ratios had no evident effect on intercalation.2. PF resins modified with MMT exhibited better water resistance. The XRD results indicated that the layers of Na-MMT were intercalated some degree rather than exfoliated. It was confirmed by measuring the plywood performance that mixing PF and PUF resins with a small percentage of Na-montmorillonite (NaMMT) nanoclay resulted in improvement of water resistance of the resins. This result was attributed to a small increase in the nanoclay interlayer distance.3. Differential scanning calorimetry (DSC) and TMA indicated that Na-MMT hads an accelerating effect on curing PF and PUF resins. The modulus of elasticity (MOE) of plywood glue joints increased with increasing curing temperatures, and the glue joints with MMT-modified resins had the maximum MOE values. The appropriate amounts of MMT used in resin synthes is ranged from 1% to 3%.4. Adding urea as an additive during PF resin synthesis helped to improve the performance of Phenol Formaldehyde (PF) /Montmorillonite(MMT) nanocomposite. Results indicated that plywood bonded with PUF/MMT resin had higher dry and wet tensile (after boiled in water for 3 hrs) strengths than those plywood bonded with PF/MMT resin. The PF molecules might have better intercalated into the nanoclay interlayer by the aid of NH2+ of urea, which was attracted to the cation of the nanoclay interlayer.5. The MMT had good compatibility with water-soluble PF resin, and partially intercalated PF/MMT nanocomposites could be obtained easily. Results indicated that plywood bonded with the PF/MMT resin synthesized by one-step process displayed higher dry and wet (3h- boil) tensile strengths than plywood bonded with the resin synthesized by the two-step process. This is attributed to the fact that during one-step synthesis small phenol and formaldehyde monomers can infiltrate easily into and polymerize in MMT layers. During the two-step process, however, bulky polymeric PF molecules can not be easily intercalated into MMT layers. It is possible that PF coupled with MMT by formation of hydrogen bonds in the intercalated layers. Although a limited effect was observed in this study, the concept of using MMT to improve the performance of PF resins was quite evident. Therefore, preparation of PF/MMT nanocomposites is worthy of further studies.