Właściwości wybranych tworzyw drewnopochodnych wytwarzanych z udziałem nano-SiO2

Abstract

As an interdisciplinary field of science, nanotechnology is applied also in wood processing. Synthetic silica (nano-SiO2) is one of the most versatile and multipurpose nanomaterials: when introduced into a polymer matrix, it improves considerably the strength and heat-resistance of resulting nanocomposites. The main objective of this research work was to determine the effect of nano-SiO2 addition to urea-formaldehyde (UF) and phenol-formaldehyde (PF) resins on the properties of plywood and particleboards produced using them, and on this basis to propose new solutions. The purpose is to reduce the amount of binders required in the production of plywood and to improve properties of particleboards produced with the particles of nonwood raw lignocellulosic materials. Considering the fact that nanosilica shows a significant tendency to agglomerate, the goal of the work was also to determine the optimal degree of silica surface modification with a selected silane coupling agent, facilitating manufacture of boards with the best physico-mechanical properties. 3-Aminopropyl-triethoxysilane (APTES) was used as an adhesion promoter and surface modifier of inorganic fillers in many types of polymer systems, including phenolic, melamine and urea-formaldehyde systems. Such modification is applied mainly in the manufacturing of polymer composites, comprising various nanofillers. The scope of works included the preparation of plywood specimens bonded with nanocomposite adhesive resins applied at different loads per unit of veneer surface, manufacture of particleboards glued with a UF resin with various amounts of nano-SiO2 added, and preparation of plywood and particleboard specimens bonded with UF and PF resins with an addition of silica modified with various amounts of APTES. Taking into consideration an increasing interest in the use of alternative materials in the wood-based materials industry, especially in particleboard manufacturing, a part of the research work was devoted to particleboards supplemented with rape straw particles bonded with UF/nano-SiO2 resin. All the particleboards made were tested for their physico-chemical and hygienic properties according to the respective technical standards. The studies demonstrated that the use of nano-SiO2 as a filler for UF and PF resins in plywood manufacturing facilitated a considerable reduction in the adhesive resin load in the veneer bonding process. Even though the consumption of the nanocomposite adhesive resins was by 33% and 25% lower for the UF and PF resins, respectively, the obtained plywood specimens showed the required bonding quality. Moreover, formaldehyde emissions from the UF resins were also markedly reduced. Given the high cost of nanosilica production, such measures are of great economic importance and they are in line with the concept of sustainable development, promoting reduced consumption of raw materials, especially those posing environmental hazards. Moreover, modification of the UF resin with a properly adjusted amount of silica improves physico-mechanical and hygienic properties of particleboards: in those enriched with annual plant waste the use of nano-SiO2 in the UF resins faciliated a higher substitution of wood chips with straw particles. Particleboards with a 50% content of rapeseed straw particles and bonded with UF/nano-SiO2 resins met the requirements for type P2 particleboards. Bonding quality as well as strength of both plywood and particleboards bonded with nanocomposite adhesive resins can be further improved by modification of nano-SiO2 with the suitable aminosilane – APTES. An interesting observation made in the research work is also that some of the combustion properties of particleboards were also improved, mainly due to high barrier properties of nano-SiO2. As indicated by the preliminary flammability tests, introduction of small amounts of nano-SiO2 into the adhesive resin provides particleboards with greater fire resistance, which is manifested e.g. in lengthening board ignition time, limiting the burned area and increasing the oxygen index.