Archive:   VOLUME:   No:   

Volume: 1996/4

Title: Influence of interaction of urea-formaldehyde resin and paraffin emulsion on the quality of particle boards
Author: Vladimir Jambreković

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.

Title: Testing the joint strength of wooden rests on bed frames
Author: Stjepan Tkalec, Ivica Grbac, Silvana Prekrat

The article presents the results of comparative research on the joint strength of wooden bed rests fixed to the bed sides. The test was done on three sample groups made of chipboards coated with fine 18 mm veneer and finished with nitrocellulose varnish. The beech (Fagus silvatica, L.) supports in the first sample were fixed with Φ 3x45 mm screws and glue varnished surfaces. The second sample group had rests fastened with two-hand Φ 1.3; 8x30 staples and glue for varnished surfaces. The samples of the third gorup were joined with Φ 8x32 mm beech dowels. The testing was done in the labs of the Faculty of Forestry Zagreb University. The results of testing for static and dynamic load have revealed that the highest joint strength for practical use was achieved by glued dowels where the mean breakforce per joint unit was 2399 N. A slightly lower strength was displayed by the screwed samples, due to different screw positioning. The break force per screw ranged from 1471 N to 1695 N. The poorest results were achieved with the staple/glue samples ranging from 925 N to 1137 N. The same samples were tested on dynamic load by means of the 50 kg-mass falling down from a height of 200 m, with a frequency of 1440 blows/h. The samples endured up to 22,218 blows before the rests were separated from the sides.

Title: Panel industries in Croatia and the new products in the world
Author: Vladimir Bruči, Salah-Eldien Omer

Croatia has sufficient good quality wood as a raw material for the production of veneer and wood boards for it\'s own needs and for export. Even though wood as a raw material which renews itself and the forestry is managed on the principle of sustained yield, this raw material has become relatively more expensive and of lower quality. The forestry production could not follow the rate of increase of the planet population, and because of the high standard there has been an increase in wood consumption. More over, Croatia has an extra pressure from the developed countries of west Europe for wood as a raw material. The basic idea, from which we start, is to take into consideration and to carry out an active politics of the exploatation of wood as a raw material as well as the development of the wood industry. Though Croatia is not a leading country either in raw material or in the production of wood-based boards and other semi-raw materials, we can suggest and develop new types of wood based materials. The reason is that we know the trends in the world and on the other hand the need of the domestic market in the situation of reconstructing Croatia.

Title: Lyctus powderpost beetles - the most frequent woodboring insects in oakwood and ashwood parquet
Author: Radovan Despot

In this article the Lyctus powderpost beetles (Lyctidae spp.) were described in short. These insects cause a fair amount of damage mainly in the oakwood and ashwood strip flooring blocks and parquet in Croatia. Due to the improvement of producers\' and users\' knowledge, all types of preventive and repressive methods against the Lyctus powderpost beetles have beeen mentioned.

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