In this research the interaction and influence of carbamide-formaldehyde resins (low molarity ratio carbamide:formaldehyde) and paraffin emulsions on the quality of V20 type of three-layer particle boards was examined. The particle boards were made from industrially produced deciduous wood chips with a large
share of high density wood. The laboratory analysis was made to determine the characteristics of wood chips, carbamide-formaldehyde resins and paraffin emulsions, together with defining the quantities of each necessary component for producing experimental laboratory particle boards. Each series of laboratory particle boards having the nominal thickness of 17 mm was produced using the same technological parameters, except for different paraffin emulsion quantities. The resin share in the outer layer of the particle boards was 11%, and in the inner layer 8,5%. Ammonium-chloride was used for polymerisation in the outer layer having the share 3 %, and in the inner layer 0,3%. Pressing time was 4 minutes and 30 seconds, using the 3,2 Mpa pressure. There were 9 series each consisting of three types of particle boards. The first type of particle boards was without paraffin emulsion. The second type of particle boards had 0,3; 0,6; 0,9 and 1,2% share of paraffin emulsion. The paraffin emulsion was made in the particle board factory.
The physical and mechanical properties were tested according to DIN standards. The formaldehyde quantity was determined according to WKI method. The achieved results show that the addition of paraffin emulsion has a great influence on increasing the hydrophobic properties of the particle boards, but it decreases the particle board mechanical properties. The particle boards with 0,9% share of paraffin emulsion (made in the particle board factory) have satisfactory properties according to DIN standards. It was not possible to determine the optimal share of paraffin emulsion (made in the petrochemical factory) in particle boards, According the DIN standards, the achieved values were not sufficient, in spite of a lower swelling thickness when the biggest share of emulsion was added. The paraffin emulsion reduces resin adhesive properties, causing an insufficient static bending strength of the particle boards. The research shows that production of the particle board according to the determined technological parameters, and using the mentioned components and wood chip types, is better when the paraffin emulsion produced in the particle board factory (rougher emulsion) is used. It can be concluded that a suitable interaction between carbamide - formaldehyde resins (low molarity ratio carbamide:formaldehyde) and the optimal quantity of paraffin emulsion can result in producing particle boards of the highest quality.