Possibility of the production of three-layer MDF

Transcription

1 Annals of Warsaw University of Life Sciences - SGGW Forestry and Wood Technology 88, 14: (Ann. WULS - SGGW, For. and Wood Technol. 88, 14) Possibility of the production of three-layer MDF NICEWICZ DANUTA, KLIMCZEWSKI MARCIN Faculty of Wood Technology, Warsaw University of Life Sciences SGGW Abstract: The paper proposes the production of a three-layer MDF instead one layer boards. Three-layer panels have been made from fibers of varying dimensions for the outer and the core layers. The outer layers were produced from standard fibers, while the core layer from longer and thicker fibers (of lower pulp freeness). In order to determine the optimal technological parameters in the production of three layer boards, the experimental plan was used in the study. Three factors at two levels were tested. Analysis of variance (ANOVA) was used to analyze the significance of factors. Regression coefficients and 3D contour plots were used to quantify the relationship between panel properties and test factors. Properties of obtained boards were tested according to the standard EN 622-5/. All selected factors within the examined range of settings had influence on MDF properties. It has been found that the best properties of the plates were x50x involving layers, the content of the glue in the outer layers of and the core layer of 12 at the time of overheating of the mats 90s. Keywords: three-layers MDF, properties of boards. INTRODUCTION The process of chips defibration is energy-consuming and is characterized by a variability of power consumption. (from 0 to 350 kwh per 1Mg of pulp) depending on the kind of raw material, type of defibrator and refiner segments and sort of produced boards (MDF, HDF, LDF) (Benker et al. 03, Johansson et al. 01, Xing et al. 06, Xing, Deng, Zhang 07). Feddersen (03) showed that in order to obtain 1 Mg fibers from the chips in the production of MDF is consumed two times more energy than 1 Mg particles in the production of particleboards. Costs reduction in the MDF production can be attained in two ways. The first possibility is modernization and optimization of defibration process, the second one is change of the structure of MDF boards. Modernization of defibration process consists in introduction of changes such : a new high-capacity screw feeder system, helical discharge from the refiner housing, new refiner segment technology, new bearing and other. The effects of these changes are: better dewatering capacity, improve the quality of fibers, reducing energy and steam consumption. Information about changing the structure of MDF is only few. Finsa company produces three layer boards in which the outer layers are made from of wood fibers, and the middle layer from particles. This technology seems to be interesting, when MDF and particleboard are produced in one factory. Medite company announced that it has two feed systems of fibers: one for the top and bottom layers, and the other one for the middle layer in the production of MDF (Wold ). Usage of fibers of varying morphology on of the outer layer and an middle layer made it possible to reduce energy consumption to 90 kwh/1mg and adhesive resin consumption by 15. So far, there have been no information on details of these solutions in the available materials. This paper proposes a three-layer MDF production of fibers with different dimensions for the outer and middle layers and with varying values of selected technological factors. 162

2 METHODS AND MATERIALS Characteristics of fibers The fibers from pine wood (Pinus silvestris), obtained in industrial conditions were applied for the production of boards. Measurement of fiber were performed in a Morfi LB01 apparatus. Average dimensions of fibers to outer layers amounted : length 1,14-1,16 mm and width µm and to core layer: length 3,9 4,7 mm and width µm. Production of boards Necessary amount of fibers for one board was weighed, separately for the outers and the core layers. The glue of 50 concentration (a mixture of UF resin with ammonium sulfate and water) was sprayed onto fibers in a laboratory blender, consisting of a rotary drum with spray nozzle. The resinated fibers were formed into mats. The mats were hot-pressed. Parameters of MDF production process are presented in Table 1. Table 1. Board production parameters Processing parameter Value Nominal density (kg/m3) 700 Thickness (mm) 16 Glue content ( of based on solid fibers): - of outer layers - of core layer or 12 Hardener NH 4 SO 4 ( of based on solid resin) 0.2 Press temperature ( 0 C) 172 Pressure (MPa) 2.5 Pressing time (s) 480 The important factors in the production of these boards were: mass participation of layers (outer and core) in the board, the amount of adhesive on the fibers of the core layer and the speed of heating of mats in the initial stage of compression, which was measured by speed of the press close. In order to determine the impact of selected factors on the properties of MDF, the experimental plan was developed. Three factors at two levels were tested. Experiment design is presented in table 2. Table 2. Full factorial experimental design with three factors and two levels Run number Content of glue in core layer () Share of layer in board Press closing time (s) () 1 /50/ /70/ /70/ /70/ /50/ /70/ /50/ 90 8 /50/

3 Properties of obtained boards were tested according to the standards EN 622-5/. Analysis of variance (ANOVA) was used to analyze the significance of factors. Regression coefficients and 3D contour plots were used to quantify the relationship between panel properties and test factors. RESULTS AND DISCUSSION The analysis of the properties of three-layer MDF was started by determining the influence of selected factors on the MOR value. Table 3: Analysis of Variance for MOR, using Adjusted SS for Tests Source DF Seq SS Adj SS Adj MS F P Glue 1 7,32 7,32 7,32 0,65 0,422 Outer layer 1 499,84 499,84 499,84 44,57 0,000 Closing time 1 452,95 52,95 52,95 40,39 0,000 Glue* outer layer 1 15,54 15,54 15,54 1,39 0,243 Glue*Closing time 1 0,36 0,36 0,36 0,03 0,859 Outer layer*closing time 1 21,86 21,86 21,86 1,95 0,167 Glue* Outer layer*closing time 1 0,07 0,07 0,07 0,01 0,935 Error ,44 807,44 11,21 Total ,38 As visible, MOR was significantly affected by two factors: mass participation of layers (outer and core ones) in the board and time of closing press. In comparison with these factors, the effect of the quantity of glue in the core layer was insignificant. Interaction between the examined factors was found. Values of MOR and a trend of changes in this property as a function of significant factors is shown in Fig MOR N/mm Fig.1. Values of MOR as a function of significant factors 90 Closing time s It can be seen in the Fig. 1 that the highest value of MOR (47 N/mm 2 )was obtained by boards of layer proportion x50x and a relatively short time of closing press plates (30s). The short fibers of the outer layers and short overheating time of mat at the initial stage compression resulted in compression of the outer layers in a high degree, which gave high values of MOR. The lowest values of MOR (38 N/mm 2 ) obtained these boards in which the 164

4 mass participation of the layers was 15x70x15 and time of closing press 90 s. Differences MOR boards in these two variants was approximately. Results of the analysis of variance which allowed determination of significant effect of factors and their interactions on MOE is shown in a Table 4. Table 4. Analysis of Variance for MOE, using Adjusted SS for Tests Source DF Seq SS Adj SS Adj MS F P Glue ,06 0,028 Top layer ,48 0,000 Closing time ,56 0,000 Glue*Top layer ,59 0,212 Glue*Closing time ,21 0,015 Top layer*closing time ,47 0,067 Glue*Top layer*closing time ,49 0,038 Error Total As visible, the modulus of elasticity of the boards depend from all tested technological factors, i.e. mass participation of layers, quantity of glue in the core layer and time of closing press plates as well as two interactions. The first interaction was between the amount of glue in the core layer and time of overheating mat, the second one between three examined factors. The effect of factors and interactions on the MOE value were not identical. Two factors mass participation of layers, and time of mat overheating had the greatest influence on MOE. Interaction between amount of glue and time of closing press had a weaker effect, quantity of glue in the core layer still weaker and interaction between three factors had the smallest influence on MOE. Occurrence of this interaction was proven but its strength in relationships between particular factors is difficult to describe. Values of MOE and a direction of changes in this property as a function of significant factors and interactions are shown in Fig. 2 (a, b, c) MOE N/mm a) Glue Closing time s 165

5 5000 MOE N/mm b) Closing time s MOE N/mm c) Glue Fig.2. Effects of factors on MOE of three-layer MDF boards In the figure 2 shows that, boards with a proportion of layers x50x had significantly higher values of MOE (4050 N/mm 2 ) in comparison with boards of layer proportion 15x70x15 (3080 N/mm 2 ). It follows that an increase in the share of large fibers in the board, by, led to a decrease of the MOE by more than. Short closing time (30s) also allowed obtaining higher results (38 N/mm 2 ) in comparison with the time of 90 s (33 N/mm 2 ). In the case of glue application in the core layer in the quantity of 12, there were obtained higher MOE values (3640 N/mm 2 ) than with an application of UF (3490 N/mm 2 ), but only about 4. Analysis of variance aiming at determination of significant factors influencing IB values is presented below. Table 5. Analysis of variance for IB, using Adjusted SS for Tests Source DF Seq SS Adj SS Adj MS F P Glue 1 0, , , ,18 0,000 Top layer 1 0, , , ,76 0,387 Closing time 1 0, , , ,16 0,692 Glue*Top layer 1 0,9338 0,9338 0, ,13 0,000 Glue*Closing time 1 0, , , ,54 0,219 Top layer*closing time 1 0, , , ,35 0,130 Glue*Top layer*closing time 1 0, , , ,91 0,343 Error 72 0, , , Total 79 0,

6 Significantly influenced on IB had one factor glue quantity in the core layer as well as three interactions: quantity of glue x share of layers, quantity of glue x time overheating of mat and share of layers x overheating time of mat. The effect of the first interaction is the strongest in comparison with two others. The influence quantity of glue and interaction between glue quantity and shares of layers on IB is presented in Fig.3 0,8 IB N/mm 2 0,6 0,4 0, Glue Fig.3. Influence of the factor glue content and its interaction with top layer on IB of three-layer MDF It can be seen in the figure 3, the structure of board (15x70x15), and glue content had no significant effect on IB. If the structure was replaced (x50x), increase in quantity of glue significantly increased IB. Values at the level recommended by the standard (0.55 N/mm 2 ) could be obtained by application of the percent share of layers x50x and the glue content in the core layer of 12. In such conditions, IB obtained value on average 0.58 N/mm 2. Analysis of variance which allowed determination of significant effects on the thickness swelling (TS) of three-layer MDF is presented in Table 6. Table 6. Analysis of Variance for TS, using Adjusted SS for Tests Source DF Seq SS Adj SS Adj MS F P Glue 1 159, , ,492 46,88 0,000 Top layer 1 1,176 1,176 1,176 0,35 0,559 Closing time 1 3,733 3,733 3,733 1, 0,298 Glue*Top layer 1,212,212,212 3,00 0,087 Glue*Closing time 1 11,119 11,119 11,119 3,27 0,075 Top layer*closing time 1,608,608,608 3,12 0,082 Glue*Top layer*closing time 1 0,000 0,000 0,000 0,00 0,999 Error 7 244, ,969 3,402 Total ,309 As visible, only the glue content in the core layer had a statistically significant effect on TS of boards. Other examined factors and interactions occurring between them did not significantly affect TS of boards. 167

7 In Fig. 4, there are shown TS values of boards in relationship to sizing degree of the core layer and shares of layers. TS 2 4 h Glue Fig.4. Influence of examined factors on TS of boards It can be seen in the figure 4, only glue quantity significantly influenced TS. With a - percent of a glue content and shares of layers 15x70x15, board swelling was the highest (18,9). With the same shares of layers but with glue content of 12, swelling decreased to 15,4. The lowest value of swelling (15,2) was recorded for boards of the structure x50x and glue content 12. SUMMARY The obtained results justify a conclusion that the idea of producing three-layer MDF by the dry method seems to be right. All selected factors within the examined range of settings had influence on MDF properties. From among the tested factors, glue content significantly affected the greatest number of board properties (MOE, IB, TS). Shares of layers and time of mat overheating influenced both MOR and MOE. In the conducted researches, there were found interactions between tested factors significantly affecting MDF properties. The most advantageous values of all tested board properties (MOR 47 N/mm 2, MOE 44 N/mm 2, IB 0.59 N/mm 2, TS 15.2 were obtained when the shares of layers amounted to x50x, glue content in the outer layers and in the core layer - 12 and time of mat overheating - 90s. REFERENCES: 1. Benker B., Erbreich M., Plinke B., Wollmann A. 03: Characterisation of wood fibres for MDF off-line and on-line measurements for production monitoring. 7 th European Panel Products Symposium, 8- th October, Llandudno, UK 2. Feddersen J. 03: Prozessenergieverbrauch in der Holzwerkstoffindustri. Diplomarbeit im Studiengang Holzwirtschaft der Universität Hamburg. Ordinariat für Holztechnologie Holzphysik Johansson O., Hogan D., Blankenship D., Snow E., More W., Qualis R., Pugh K., 168

8 4. Wanderer M. 01: Improved process optimization through adjustable refiner plates. International Mechanical Pulping Conference Helsinki. Finland (Sonderdruck von J&L Fiber Services) 5. Wold D. : The EVO 56 Defibrator system the obvious choice at Medite; Metso Results Pulp & Paper 3/: ( 6. Xing Ch., Deng J., Zhang S. Y, Riedl B, Cloutier A. 06: Properties of MDF fromblack spruce tops as affected by thermomechanical refining conditions. Holz Roh Werkst 64: Xing Ch, Deng J., Zhang S. Y. 07: Effect of thermo-mechanical refining on properties of MDF made from black spruce bark. Wood Science Technology 41: EN-622-5:06 Fibreboards -Specifications-Part 5. Requirements for dry process boards (MDF) Streszczenie: Możliwości produkcji 3-warstwowych MDF. W pracy podjęto próbę wyprodukowania, w warunkach laboratoryjnych, trójwarstwowych płyt MDF zamiast jednowarstwowych. Do wytwarzania płyt zastosowano włókna drzewne pozyskane z drewna sosny (Pinus sylvestris) w warunkach przemysłowych. Na warstwy zewnętrzne wykorzystano włókna standardowe, a na warstwę wewnętrzną włókna odpowiednio dłuższe i grubsze. Płyty wytwarzano według planu doświadczalnego, w którym przyjęto trzy czynniki zmienne na dwóch poziomach: procentowe udziały warstw (zewnętrznych i wewnętrznej) w płytach, stopień zaklejenia warstwy środkowej i czas przegrzewania kobierców przed ich sprasowaniem. Zbadano właściwości płyt zgodnie z obowiązującą normą EN Analizę wariancji (ANOVA), zastosowano do analizy wpływu badanych czynników na właściwości płyt. W wyniku badań stwierdzono, że wszystkie czynniki w badanym zakresie miały wpływ na właściwości płyt. Płyty o najlepszych właściwościach uzyskano, gdy udział warstw wynosił /50/, stopień zaklejenia warstw zewnętrznych, warstwy środkowej -12 i czas przegrzewania kobierców 90s.. Corresponding authors: Marcin Klimczewski, Danuta Nicewicz Faculty of Wood Technology, Warsaw University of Life Sciences SGGW Warsaw, Nowoursynowska str. 159 Poland danuta_nicewicz@sggw.pl marcin_klimczewski@ sggw.pl 169