1. Limiting the Formaldehyde Emission of Wood Based Panels – Developments in Adhesives Technologies
, Pesaro, Italy
Andreas Zillessen, Harald Schwab
Quality Assesment
Fraunhofer Institute for Wood Research
Wilhelm-Klauditz-Institut WKI
Braunschweig

2. Content Introduction Process Engineering Scavengers Isocyanates
Biogenic Adhesives
Other Possibilities
Summary

3. Introduction - Formaldehyde Emission-
Toxic
Respiratory Irritation
Carcinogenic (IARC Group 1)
Marutzky 2008
E1 : Blue Angle: CARB (Phase II):
0.1 ppm ppm (EN 717-1) ppm (ASTM E 1333)

4. 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

5. Process Engineering
Various parameters of the production process of wood based panels influence the formaldehyde emission
Raw materials
Flake drying
Hot press conditions
Density profile
Easy to implement
May slow down production process or increase the costs

6. Process Engineering Process Parameter CH2O-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.

7. 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

8. 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

9. Isocyanates - as additives -
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
Lower cost compared to PMDI
Improved mechanical properties
Higher costs compared to UF resins
Poor processability
Toxicity of monomers

10. Biogenic Adhesives - Overview -
Different bio-based adhesives can be used for the production of wood based panels
Proteins
Tanins
Lignins
Starch and other Polysaccharides
Bio based raw materials
Variations in the quality of the raw materials
Limited availability

11. 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

12. Biogenic Adhesives - Tanins -
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.
Reactivity
Versatility
High costs

13. Biogenic Adhesives - Lignins -
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.
Low Costs
Availability
Low reactivity
Strong variations in quality

14. Biogenic Adhesives - Starch -
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.
Availability
Low moisture resistance
Competition with food production

15. Other Possibilities Alternative adhesives PF resins MUF resins PVAc
Substitution of Formaldehyde
Other aldehydes
Hexamine
Coatings

16. Summary Thank you For your Attention
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