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© Fraunhofer WKI , Pesaro, Italy Andreas Zillessen, Harald Schwab Quality Assesment Fraunhofer Institute for Wood Research Wilhelm-Klauditz-Institut WKI Braunschweig Limiting the Formaldehyde Emission of Wood Based Panels – Developments in Adhesives Technologies
© Fraunhofer WKI Content Introduction Process Engineering Scavengers Isocyanates Biogenic Adhesives Other Possibilities Summary
© Fraunhofer WKI Introduction - Formaldehyde Emission- Toxic Respiratory Irritation Carcinogenic (IARC Group 1) Marutzky 2008 E1 :Blue Angle:CARB (Phase II): 0.1 ppm 0.05 ppm (EN 717-1) ppm (ASTM E 1333) Formaldehyde:
© Fraunhofer WKI Introduction - Adhesives for Wood Based Panels - ~ 90% of the WBP are produced using UF resins + Availability of raw materials + High reactivity + Low Costs ! Formaldehyde emission Moisture resistance Marutzky 2007
© Fraunhofer WKI Process Engineering Raw materials Flake drying Hot press conditions Density profile Various parameters of the production process of wood based panels influence the formaldehyde emission + Easy to implement May slow down production process or increase the costs
© Fraunhofer WKI Process Engineering Process ParameterCH 2 O-Emission density of the top layer moisture content before pressing hot pressing temperature hot pressing time For some parameters the magnitude of the influence strongly depends on the F/U ratio.
© Fraunhofer WKI Scavengers Scavengers can be added to the resin or the dried flakes Formaldehyde scavengers react with the free formaldehyde in the panel Amine containing chemicals or polyphenols like tannins can be used as scavengers + Simple method to reduce formaldehyde emission Higher costs May influence other properties
© Fraunhofer WKI Isocyanates - as alternative adhesives - Adhesives based on MDI and its oligomers can be used as resins for the production of flake and fibre boards. During the curing process the MDI reacts with water to form a polymeric network. PMDI reacts with several types of surfaces. n = 0-9 PMDI + No formaldehyde + Moisture resistance + Improved mechanical properties Higher costs Poor processability Toxicity of monomers
© Fraunhofer WKI PMDI can also be used as an additive for UF resins The addition of PMDI increases the mechanical properties PMDI also act as an accelerator for UF resins UF resins with lower F/U ratios can be used in combination with PMDI Mixtures of PMDI and UF resins have to be processed quickly due to their low stability Isocyanates - as additives - + Lower cost compared to PMDI + Improved mechanical properties Higher costs compared to UF resins Poor processability Toxicity of monomers
© Fraunhofer WKI Proteins Tanins Lignins Starch and other Polysaccharides Biogenic Adhesives - Overview - Different bio-based adhesives can be used for the production of wood based panels + Bio based raw materials Variations in the quality of the raw materials Limited availability
© Fraunhofer WKI Biogenic Adhesives - Proteins - Proteins have been used as wood adhesives since historical times. Proteins from animals (casein, albumin) or plants (wheat, soya, corn) can be used as source for raw materials. Protein dispersion can be used as adhesives purely or in combination with crosslinking agents like formaldehyde. Most promising are mixtures of proteins with PF resins. + Good adhesion to wood Low moisture resistance High alkali content Competition with food production
© Fraunhofer WKI Tanins are polyphenolic compounds which can be extracted from wood (e.g. quebracho) or bark (e.g. mimosa). Tanins can be used as formaldehyde based resins or with other reactants like hexamine. Tanins also undergo an autocondensation reaction which can be catalyst by different hardeners. Tanins also can be used as additive to conventional UF resins to reduce the formaldehyde emission. Biogenic Adhesives - Tanins - + Reactivity + Versatility High costs
© Fraunhofer WKI Lignins are polyphenols and one of the major components of wood and accrue during the paper production process. Lignins show a very low reactivity, e.g. towards formaldehyde, and cannot be used in industrial production processes so far Lignins can be used in combination with other adhesives, e.g. UF,PMDI or PF. Biogenic Adhesives - Lignins - + Low Costs + Availability Low reactivity Strong variations in quality
© Fraunhofer WKI Starch and other polysaccharides can directly be used as wood adhesives. Mostly starch is used as modifier for other adhesives, eg. UF or PF. Polysaccharide can also be used as raw material for the production of chemicals for other adhesives systems, eg. furanic resins. Biogenic Adhesives - Starch - + Availability Low moisture resistance Competition with food production
© Fraunhofer WKI Other Possibilities Alternative adhesives PF resins MUF resins PVAc Substitution of Formaldehyde Other aldehydes Hexamine Coatings
© Fraunhofer WKI Summary There are several ways to further decrease the formaldehyde emission of wood based panels produced with UF resins. Further decrease in the formaldehyde content Use of scavengers Combinations of UF resins with PMDI or other adhesives If the requirements concerning the formaldehyde emission increase further other adhesives system become more interesting PMDI Combinations of biogenic adhesives and conventional resins Thank you For your Attention
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