Decorative Veneer Properties of Black Walnut (Juglans nigra L.)

Transcription

1 Roman Réh, Assoc. Prof., PhD. Technical University in Zvolen, Slovakia Decorative Veneer Properties of Black Walnut (Juglans nigra L.) 2014, June 23 th Aula Building

2 - Black walnut (Juglans nigra L.) - interesting species for wood processing worldwide - fully recommended for the European woodworking industry - the quality of decorative veneers made from black walnut does not differ from the quality of the commonly used veneer for veneering in furniture industry when correct thickness is selected - In Europe, because of the shortage of the high quality traditional raw material for decorative purposes, it is the time to start to utilize the suitable minor trees from the European forests.

3 - for Central European wood-processing industry is black walnut an introduced species - it has it specific interesting particularities: a. it is the only North American dark wood and b. in Europe it does not have any natural pests while growing

4 MATERIALS AND METHODS - raw material for this research - Slovak origin - from Arborétum Mlyňany - 12 veneer logs with a length of 140 cm and with a diameter of cm were dipped for a period of 2 months at the water temperature 20 o C - veneers were manufactured by off-center rotary cutting in the Development workshops and laboratories of the Technical University in Zvolen - new and interesting grains and textures of black walnut were obtained - veneers with the thicknesses of 0.6, 0.7, and 0.8 mm were dried up to a moisture content of 10 1 % by drying at a temperature 100 C

5 Off-center rotary cutting

6 Off-center rotary cutting

7 - veneers were subjected to a number of technological test procedures - aim - to determine the most appropriate thickness of offcenter cutting (eccentrically peeled) black walnut decorative veneer and values of optimal glue mixture spread which is needed for veneering technology - Specific glue penetration to the veneered area - it was tested the range from 100 to 220 g.m -2 - veneering with urea-formaldehyde glue was carried out under the following conditions: - press pressure: 0.6 MPa - pressing temperature: 130 C - pressing time: 4 min

8 Table 1. Results of the specific glue penetration to the veneered area in dependence on the spread thickness Veneer Thickness (mm) Glue Spread (g.m -2 ) no substantial glue penetration within the spread range g.m -2 - there is no danger of devaluation of the veneered elements - glue spread g.m -2 was proposed for particleboard

9 - Moisture absorption of veneer - to determine the equilibrium moisture content of the test specimens during long-term storage of veneer sheets in an environment in which the desired temperature and the desired relative MC of air exists - chamber with a relative humidity of 95 ± 2 % and at a temperature of 20 ± 2 C for 30 days - drying to zero moisture content - moisture absorption n w (%) calculation (formula) n w m m m w o o.100 (1) where m w is specimen weight after conditioning and m o is specimen weight after oven drying

10 Table 2. Statistical characteristics of moisture absorption of black walnut veneer Thickness x V x n [mm] [%] [pcs] the values of moisture absorption are decreasing insubstantially with the increasing veneer thickness - the variation coefficient is at an acceptable level - the value of moisture absorption is relatively low - it corresponds to the equilibrium moisture content determined from sorption isotherm for lower range of standard test conditions (22.20 %) according to DeBoer and Zwicker isotherm

11 - Tensile strength of veneers perpendicular to the grain - to determine the tensile strength at maximum load which is exposed to the test specimen up to the failure of its strength perpendicular to the grain Table 3. Statistical characteristics of tensile strength of black walnut veneers perpendicular to the grain (w = 12 %) Thickness [mm] x [MPa] V x [%] n [pcs] (x Average value; V x - Variation coefficient; n Number of measurements)

12 - tensile strength of black walnut veneers perpendicular to grain could be theoretically equal to the tensile strength of wood in the same direction - experimental results have shown that the average strength of veneers is significantly lower than the strength of the wood - this difference increases with decreasing veneer thickness - cracks play a negative role in the case of tensile strength of veneers whose frequency depends to a large extent on the veneers production technology

13 - most important in terms of the mechanical properties of decorative veneer is that veneer must withstand as compact as possible during handling - from this perspective tensile strength of black walnut veneers perpendicular to the grain is decisive - mechanical properties of decorative veneers are negligible after veneering

14 CONCLUSIONS - selected introduced woody species suggest good perspectives in the coming years and the future quality and volume production may be secured providing systematic and intense tending of forest stands takes places - black walnut is suitable for veneering of composites (particleboard, MDF) - it is suitable for application in the furniture industry either as a replacement for some commonly used woody species or as a woody species widening the assortment of woody species utilized in furniture industry

15 Thank you for your attention. Acknowledgements Roman Réh, Assoc. Prof., PhD. Technical University in Zvolen Faculty of Wood Science and Technology SK Zvolen The research described in the paper presented was supported by grant No. 01/0345/12 from the Slovak Grant Agency (Interaction of the Components of Wood and High Temperatures during Pressing of Wood Composites and its Effect on the Formation of Composites Avoiding the Chemical Changes in Composition of Pressed Wood Particles and Elimination of the Fire Risk). The author would like to thank the grant agency for the support of this research.