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Application of glycerol in adhesives for wood panels KATSAMPAS ILIAS Foggia, Italy , April 2009 CONTENTS • • • • • • • CHIMAR HELLAS profile INTRODUCTION FORMALDEHYDE BASED ADHESIVE RESINS FORMALDEHYDE BASED ADHESIVE RESINS AND GLYCEROL NATURAL RESINS AND GLYCEROL GLYCEROL DERIVATIVES AND WOOD ADHSIVES CHIMAR R&D on “green” panel resins CHIMAR HELLAS profile • Developer and Provider of Industrial Technology for resins and chemicals for wood-based panels • Technology licensing, manufacturing support, application support for: formaldehyde resins, resin additives, field processes • Industrial Engineering and Plant Procurement: formaldehyde, UFC, resins, chemical additives • Research & Development: develops know-how in house • Training of client personnel • Technical support: remotely and on-site • Product testing: as per international standards INTRODUCTION WOOD ADHESIVE TECHNOLOGY : •The recorded history of bonded wood dates back at least 3,000 years to the Egyptians, and adhesive bonding goes back to early mankind (Skeist, I. and Miron, J. (1990). Introduction to adhesives. In: Skeist, I. (Ed.), Handbook of Adhesives. (3rd) Van Nostrand Reinhold, New York, chap 1.) •The conventional wood-based composite products are typically made with a thermosetting or heat-curing resin or adhesive that holds the lignocellulosic (wood) fibre together. •Wood composites are grouped into three general categories: plywood, particle and fibre composite •Commonly used resin–binder systems include phenol-formaldehyde, urea-formaldehyde, melamine-formaldehyde, and isocyanate. Examples of various wood composite products. plywood, OSB, particleboard, MDF, and hardboard. FORMALDEHYDE BASED ADHESIVE RESINS FORMALDEHYDE BASED ADHESIVE RESINS REPRESENT BY FAR (>95%) THE BIGGEST VOLUMES WITHIN THE WOOD ADHESIVES UF RESIN ADHESIVES: 85% MELAMINE BASED RESIN ADHESIVES: 10% PHENOL BASED RESIN ADHESIVES: <5% Condensation resins based on formaldehyde are formed by the reaction of formaldehyde with various chemicals like urea, melamine, phenol or combination of these substances. FORMALDEHYDE BASED ADHESIVE RESINS AND GLYCEROL •Glycerol in aminoplastic resins Glycerol is used a) as flexibilizer into the stiff chain of aminoplastic resins b) to improve the hydrophobicity c) to decrease the curing time Improving the performance of MUF resins, with the use of polyols, glycerol, 1,2,6-hexanetriol, sorbitol and others. Act as more effective solvents for melamine and higher molecular weight melamine resin fractions, they disrupt the colloidal state of MUF resins, both of which facilitate the homogeneous phase reactions and ensure better uniform network formation during curing. All of these additives function by addition to the end of the resin after preparation, or by addition to the glue-mix before resin application Glycerol derivatives can also be used as "latent", acid liberating hardeners for curing melamine resins. 3-Chloro-1,2-propanediol is also known as glycerol-αmonochlorohydrin and Glycerol dichlorohydrin (1,3-dichloro-2-propanol) •Glycerol in impregnation resins Woodbase materials, especially chipboard, which are coated with aminoplasticimpregnated paper webs are used in the manufacture of, for example, furniture components and work surfaces. Compounds containing hydroxyl groups, primarily glycols, or amido- or amino groups serve as plasticizers for impregnated papers. Glycerol is used most widely, however, due to the comparatively high cost of glycerol; it is combined with other cheap substances. One of the most readily available additives for glycerol based plasticizers is synthetic urea. • Glycerol as formaldehyde catcher The addition of glycerol reduces further the formaldehyde emissions by binding up remaining free volatiles into the polymer matrix and/or reacting with formaldehyde moieties to produce less volatile cyclic and polymeric formals. NATURAL RESINS AND GLYCEROL •Soy flour (SF) resins SF resins was found to be brittle, weak and difficult to process into useful binder. Glycerol has been reported to increase the flexibility and extensibility of soy protein plastics by reducing the interaction between protein molecules. The addition of glycerol provides better tensile and flexural properties on the composites binded with the natural resin. •Glyoxal/glycerol/ boric acid Interesting and environmentally friendly mixture suitable for wood dimensional stabilization. •Natural tackifying resin A potential additive in natural wood adhesives could also be the glycerol ester of gum resin which is made from gum resin or refined gum resin through esterification with glycerol GLYCEROL DERIVATIVES AND WOOD ADHESIVES • Hyperbranched polyether with hydroxyl end groups Hyperbranched polyether (HBP) obtained from glycerol blended with ureaformaldehyde improves the hardness (16%) and the compressive shear strength (17%) of the cured urea - formaldehyde polymer, whereas water absorption remains unaffected. Glycerol triacetate (triacetin) Used as a cure accelerator in various binder formulation such phenol – formaldehyde and tannin or lignin binder systems. Poly-glycerol and poly-glycerol ethers and esters Very interesting compound due to their high content of hydroxyl groups that can react either with formaldehyde (scavenger) or with urea or melamine to improve overall resin properties. •Diglycidyl ether (DGE) and polyglycidyl ether (PGE) type compounds Due to the reactivity of diglycidyl and polyglycidyl ether compounds with hydroxylated reactants like Lignin and or Tannin, they can potentially be applied in the wood adhesives field. •Polyethyleneglycols (PEGs), polyglycerol methacrylate (PGMA) Improve the dimensional stability of wood and its hydrophobicity CHIMAR R&D on “green” panel resins Resins derived from natural products or by-products: Tannin Lignin Cellulose Spent pulping liquor from paper production Biomass pyrolysis oil (bio-oil) and its fractions Extraction/liquefaction products of agricultural and forestry residues (cashew nut shell liquid (CNSL), liquefied wood, liquefied olive stones, vinasse) Starch Proteins (soy) Ilias Katsampas Chemical Engineer, PhD, Msc R&D department Chimar Hellas SA Sofouli 88, 55131 THESSALONIKI .: +30-2310424167, +30-2310424149 e-mail: [email protected], [email protected] www.chimar-hellas.com