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Mechanical properties and decay resistance of wood–polymer composites prepared from fast growing species in Turkey
Bioresource Technology 96 (2005) 1003–1011
Mechanical properties and decay resistance of wood–polymer composites prepared from fast growing species in Turkey ¨ mit C. Yildiz, Sibel Yildiz, Engin D. Gezer U
*
Department of Forest Industrial Engineering, Faculty of Forestry, Karadeniz Technical University, 61080 Trabzon, Turkey Received 29 September 2003; received in revised form 24 September 2004; accepted 24 September 2004 Available online 11 November 2004
Abstract Some mechanical properties of wood–polymer composites from maritime pine (Pinus pinaster Ait.) and poplar (Populus x. euramericana cv. I-214) wood were investigated. Three different monomers; styrene (ST), methyl methacrylate (MMA) and styrene/ methyl methacrylate (ST/MMA) mixture were used in preparation of wood–polymer composites (WPCs). Full-loading (FL), half-loading (HL) and quarter-loading (QL) were used as polymer content levels. Untreated pine and pine–polymer composite samples were tested in compression strength parallel to grain and static bending strength. WPCs mechanical properties increased compared to untreated wood. The polymer had greater effect on the strengths of the ST/MMA treated pine than on the ST and MMA treated pine samples. Increasing of the mechanical properties should improve the structural competitiveness of WPCs made from fast growing-low density woods. Weight losses due to fungal attack for pine and poplar–polymer composites were also determined. Although polymers at full and half loading levels helped decreasing weight losses due to both fungi for each wood species, weight losses were still found to be higher. 2004 Elsevier Ltd. All rights reserved. Keywords: Wood–polymer composites; Styrene; Methyl methacrylate; Maritime pine
1. Introduction Over the years wood has been treated with a variety of chemicals to change its physical characteristics. From 1930 to 1960 a number of new wood treatments were introduced: acetylation of the hydroxyl groups, ethylene oxide addition to the hydroxyl groups, polyethylene glycol bulking of the cell-wall, the phenol formaldehyde treatments under the name of Impreg and Compreg, and wood–polymer composites (WPCs). WPCs are prepared by impregnating of wood with vinyl monomers * Corresponding author. Address: Engin Derya Gezer, Kafkas University, 08000 Artvin, Turkey. Tel.: +90 535 830 2555; fax: +90 466 212 6951/462 325 7499. E-mail address: [email protected] (E.D. Gezer).
0960-8524/$ - see front matter 2004 Elsevier Ltd. All rights reserved. doi:10.1016/j.biortech.2004.09.010
followed by free radical bulk polymerization in the lumens and cell-walls. By adding bulk vinyl polymers to the void spaces in wood, compression strength, hardness, and abrasion resistance are greatly improved. The diffusion of the water in and out of the WPCs is restricted. WPCs have found commercial application where the specific physical property improvements can be used to advantage. Parquet flooring is a major commercial product. Other commercial items include archery bows, billiard cues, golf clubs, musical instruments, office equipment, and knife handles. With the finish integrated through the WPCs, maintenance problems are kept to a minimum. WPCs are produced in United States, Germany, England, Poland, Italy, Japan, Taiwan, New Zealand and other countries (Meyer, 1982). Several review articles on WPCs have
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been published (Meyer, 1981; Rowell and Konkol, 1987; Schneider, 1994; Kumar, 1994; Lu et al., 2000). From the viewpoint of the method of production of WPCs, the most decisive factor in choosing a suitable wood for raw material is its homogenous impregnability. Hardwoods (deciduous species) have mainly been used in making WPCs. Many woods, including tropical species, have been found useful to make WPCs, such as alder, yellow poplar, ash, maple, walnut, birch, basswood, red gum, beech, red and white pine (Rowell and Konkol, 1987). However, a few studies dealing with the suitability of fast growing wood species have been done (Kumar, 1994; Elvy et al., 1995). The main objectives of this study were (i) to prepare WPCs from maritime pine and poplar as important fast growing wood species in Turkey, (ii) to evaluate the mechanical properties of this pine–polymer composite materials, (iii) to evaluate their decay resistance.
2. Methods 2.1. Wood materials Ten 28-year-old maritime pine (Pinus pinaster Ait.) trees from the original plantation areas in Kerpe Burnu, Kocaeli where is western part of Turkey and ten 9-yearold poplar (Populus x. euramericana cv. I-214) trees from the original plantation areas in Meric, Ipsala where is western border of Turkey were cut down as wood material. were cut down as wood material. Two blocks (each 65 cm long) from the sapwood portion of each log were sawn for mechanical tests. These blocks were airseasoned to equilibrium moisture content prior to preparing of samples. Test and control samples were prepared from these blocks for each mechanical property according to the relating standards. The prepared test and control samples were dried at 103 ± 2 C to determine the oven-dried weights before polymerization (WBP). Test samples were then conditioned until they had 7% moisture content prior to monomer impregnation. 2.2. Monomer solutions Three monomer solutions were used for wood–polymer composite production: styrene (ST), methyl methacrylate (MMA) and styrene/methyl methacrylate (ST/ MMA, 65/28 (w/w) %) mixture containing 2% benzyl peroxide catalyst (polymerization initiator) and 5% divinyl benzene as cross-linker. Monomer solutions were used with the addition of benzene in order to adjust the three different polymer loading levels in WPCs; the full-load level (FL) consisted of 100% monomer solution, the half-load level (HL) 70% monomer solution,
30% benzene, and the quarter-load level (QL) 40% monomer solution, 60% benzene in weight bases. 2.3. Impregnation and polymerization procedure Test samples were placed in a vacuum-chamber and, a full vacuum (<70 mmHg) was drawn on the wood for 30 min. The monomer solutions were introduced into the treatment chamber until the samples were completely covered. The samples were then soaked in monomer solution for 24 h in normal atmosphere and room temperature conditions. The impregnated samples were wrapped in aluminum foil and heated to 90 C for 24 h to polymerize the monomer. After unwrapping, the samples were dried at 103 ± 2 C to remove residual monomer and determine the oven-dried weights after polymerization (WAP). The polymer content (PC) in the test samples was calculated by the formula (Duran and Meyer, 1972): PC% ¼
WAP WBP 100; WBP
where WAP, the oven-dried weights of wood sample after polymerization; WBP, the oven-dried weights of wood sample before polymerization; PC, The polymer content. 2.4. Mechanical tests The following mechanical properties of WPCs and their controls were tested: (i) compression strength parallel to grain with the samples milled to 20 · 20 · 30 mm, (ii) static bending strength with the samples 20 · 20 · 300 mm. Compression and bending tests were performed in accordance with American Society for Testing and Materials 143 (1996). 2.5. Laboratory fungal decay resistance tests Decay resistance was assessed using European Standard EN 113 (1994), with Coniophora puteana for 3 · 2 · 5 cm cut pine wood samples and Coriolus versicolor for 3 · 2 · 5 cm cut poplar wood samples as the test fungi. Four control and four test samples for each group were used. The wood samples and Kolle flasks were sterilized. Each Kolle flask containing malt extract agar was inoculated with an agar disc cut from the actual growing edge of the test fungus and Kolle flasks were incubated at 20 ± 2 C and 65 ± 5% relative humidity until malt extract agar was covered by mycelium. Sterilized test blocks were then placed in the Kolle flask and incubated at 20 ± 2 C and 65 ± 5% relative humidity for 16 weeks. One test wood polymer composite sample and one control were placed inside each Kolle flask. After the incubation period, test blocks were removed and conditioned at 25 ± 2 C and 65 ± 5% relative
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humidity for 2 weeks. Changes between initial and final conditioned weight served as a measure of fungal attack.
3. Results and discussion The polymer content values for pine and poplar obtained in each test samples are given in Table 1. Polymer content for pine and poplar varies greatly among the
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polymer loading levels. It was found that the polymer contents for poplar were higher than that of pine because poplar specific gravity is lower than pine. However, there was no significant differences in polymer contents for the same polymer loading levels although wood dimensions were different (i.e. static bending strength wood samples ST and compression strength wood samples ST etc.) for both wood species. It was also found that ST/MMA mixture had slightly higher
Table 1 Polymer content values for pine and poplar of test samples Wood species
Mechanical property
Polymer type
Polymer loading level
Polymer content (in percentage of initial oven-dried weight) Mean
Pine
Compression strength
Static bending strength
Poplar
Compression strength
Static bending strength
a
Std. dev.
Homogeneity groupsa
ST
FL HL QL
111 87 39
6 5 7
AB C E
MMA
FL HL QL
107 69 44
8 5 3
B D E
ST/MMA
FL HL QL
109 91 44
5 5 3
AB C E
ST
FL HL QL
104 88 34
12 6 4
B C E
MMA
FL HL QL
117 84 36
9 9 4
A C E
ST/MMA
FL HL QL
118 98 63
12 9 7
A BC D
ST
FL HL QL
157 88 63
14 22 9
BC F G
MMA
FL HL QL
169 99 45
20 26 13
AB EF H
ST/MMA
FL HL QL
167 136 49
17 28 15
ABC D H
ST
FL HL QL
128 97 50
46 23 17
D EF H
MMA
FL HL QL
158 107 43
20 24 18
BC E H
ST/MMA
FL HL QL
179 140 97
22 33 32
A D EF
Means with the same letter are not significantly different at p < 0.05. Comparisons were done within the each wood species group.
Table 2 Effect of polymer content on compression strength of the pine– polymer composites Wood species
Pine
Poplar
Polymer type
Compression strength, kg/cm2, at 12% MCa Mean
Std. dev.
Homogeneity groupsb
Control ST
0 FL HL QL
378 552 509 413
33 36 34 28
A E D B
MMA
FL HL QL
483 463 419
52 30 33
CD C B
ST/MMA
FL HL QL
625 546 478
57 41 43
F E C
Control ST
0 FL HL QL
278 451 340 352
17 28 22 38
A E B B
FL HL QL
500 377 363
45 25 23
F CD BC
MMA
ST/MMA
a
Polymer loading level
FL HL QL
545 377 399
38 35 38
G CD D
Moisture content. Means with the same letter are not significantly different at p < 0.05. Comparisons were done within the each wood species group. b
90 80 70 60 50 40 30 20 10 0
ST MMA MMA/ST
100
50 Polymer loading levels
25
Fig. 1. The percentage increase in compression strength of pine– polymer composites.
polymer loading levels and compression strength for all polymer types. The data (Table 2) also showed that the highest value in compression strength was observed in ST/MMA poplar samples as 545 kg/cm2, and approximately two times greater than that of untreated. It was determined that there were significant differences between full load and half and quarter loads polymer types; however, there were no significant difference between half loads and quarter loads for all polymer types. Percentage changes in compression strength of poplar–polymer composites are given in Fig. 3. The increasing rates varied between 22% and 107%. The highest rate was obtained in FL level of ST/MMA mixture. The highest rate was obtained in FL level of ST/MMA mixture. This can be attributed to two main reason: the higher polymer content in ST/MMA composite samples and, that ST/MMA mixture has strong branched polymeric situation (Baysal, 1981). The percentage increase in the compression strength compares favorably with the 28–124% reported by different researchers (Autio and Miettinen, 1970; Siau et al., 1968; S ß olpan and Gu¨ven, 1999; Schneider et al., 1990; Kinell and Aagaard, 1969; Lawniczak, 1973). It was reported that the gross wood probably fails in compression due to the buckling of relatively thin cell walls because of a long-column type of instability. The addi-
Compressive Strength (kg/cm2)
polymer content than the others, because the polymerizing rate of this monomer mixture was higher than those of ST and MMA monomers (Yildiz, 1994). The test results relating to the effect of polymer content changes in pine– and poplar–polymer composites on their compression strength parallel to grain determined from 16 repetitions were summarized in Table 2. The highest value in compression strength was observed in ST/MMA pine samples as 625 kg/cm2, and approximately two times greater than that of untreated. It was determined that there were significant differences among the polymer loading levels for all polymer types except MMA half load and MMA full load. It is fairly certain that the compression strength value increases as a result of increase in polymer content. Percentage changes in compression strength of pine–polymer composites are given in Fig. 1. The increasing rates vary between 17% and 75%. The highest rate was obtained in FL level of ST/MMA mixture. In addition, the relationship between polymer loading levels and compression strength for all polymer types and their regression equations for each polymer type were determined (Fig. 2). It was found that there was a linear relationship between
%
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1006
700 650
ST/MMA = 2.3897x + 402.2 R2 = 0.95
600 550 500 450 400
ST = 1.8194x + 383.4 R2 = 0.92
350
MMA = 1.0366x + 390.4 R2 = 0.90
300 0
20 40 60 80 Polymer Loading (%w/w-polymer/od wood)
100
Fig. 2. Relationship between polymer loading levels and compression strength.
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MMA MMA/ST
%
80 60 40 20 0
100
50 Polymer loading levels(%)
25
Fig. 3. The percentage increase in compression strength of poplar– polymer composites.
Compressive Strength (kg/cm 2)
tion of polymer places a coating on the walls which thickens them, greatly increasing their lateral stability (Siau et al., 1968). In addition, the relationship between polymer loading levels and compression strength for all polymer types and their regression equations for each polymer type were determined (Fig. 4). It was observed for poplar wood polymer also that the compression strength value increases as a result of increase in polymer content. However, this situation was not clear between the HL and the QL levels. Table 3 summarizes MOR and MOE for both pine and poplar polymer composites and their controls. The MOR strength increased from an average of 512 kg/cm2 for untreated pine to an average of 683 kg/ cm2 for ST/MMA impregnated pine wood polymer samples. The results showed that there were significant difference among the polymer loading levels for ST. However, there was no significant difference between half and quarter loading level for MMA, but there was significant difference between full loading and half, quarter loading levels. For MMA/ST polymer type, while there was no significant difference between full loading and half loading level, there was significant difference between quarter loading and half, full loading levels. The highest percentage increase in MOR for
600 MMA/ST = 2.4446x + 292.8 R2 = 0.89
550 500 450 400 350 300
MMA = 2.1051x + 287.4 R2 = 0.97
250 200 0
ST = 1.5966x + 285.4 R2 = 0.90
20 40 60 80 Polymer Loading (%w/w-polymer/od wood)
100
Fig. 4. Relationship between polymer loading levels and compression strength.
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pine–polymer composites was found to be 32% for half load MMA/ST polymer type (Fig. 5). The lowest percentages increase in MOR were found to be full loading levels for ST and MMA/ST. The increasing rates varied between 9 and 32%. Regression analysis showed that there was a linear relationship between polymer loading levels and MOR for MMA pine wood polymer (Fig. 6). However, for both ST and ST/MMA, there was an increase from 0% to 50% of polymer loading levels. Once polymer loading levels reached 50%, MOR tended to decrease. It can be concluded that the dominant factor is the homogenous distribution of the polymer through the wood structure compare to polymer content level. MOR increased from an average of 326 kg/cm2 for untreated poplar to an average of 547 kg/cm2 for ST/ MMA impregnated poplar wood polymer samples. The results showed that there were significant differences among the polymer loading levels for all polymer types. Percentage increase in static bending strength of the treated samples are given in Fig. 7. The highest percentage increase in MOR for poplar was found in samples impregnated with full load MMS/ST. The increasing rates varied from 10% to 44%. In addition, regression analysis showed that there was a linear relationship between the polymer loading levels and MOR values for all polymer types (Fig. 8). These percentage changes are similar to those changing between 18% and 51% reported by the other investigators (Autio and Miettinen, 1970; Siau et al., 1968; Schneider et al., 1990; Lawniczak, 1973; Brebner et al., 1985, 1988). The wood–polymer composite samples usually failed first in tension on the bottom of the samples and there was no evidence of crushing or gross compression failures. The presence of polymer in the wood had apparently stiffened the thin cell-walls sufficiently to prevent buckling under a compressive load. This probably accounts for the relatively large increases in the static bending strength of the WPCs (Siau et al., 1968; Schneider et al., 1990). The MOE strength increased from an average of 55 303 kg/cm2 for untreated pine to an average of 82 207 kg/cm2 for ST/MMA impregnated pine wood polymer samples. The results showed that there were significant difference between quarter loading level and half, full loading levels for ST monomer. However, there was no significant difference between half and quarter loading level for both MMA and ST/MMA polymer types, but there was significant difference between full loading and half, quarter loading levels. The highest percentage increase in MOE for pine–polymer composites was found to be 24% for full load MMA/ST polymer type (Fig. 9). The lowest percentages increase in MOE were found to be half loading levels for ST monomer. The increasing rates varied between 6% and 24%. Adams et al. (1970) also reported that the MOR for MMA impregnated loblolly pine wood samples showed the
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Table 3 Effect of polymer content on static bending strength of the pine–polymer composites Wood species
Pine
Poplar
a b
Polymer type
Polymer loading level
Static bending strength, kg/cm2, at 12% MCa MOR
Std. dev.
Homogeneity groupsb
MOE
Std. dev.
Homogeneity groupsb
Control ST
0 FL HL QL
512 510 630 600
57 29 43 82
A A E D
55 303 62 988 65 480 58 827
4877 3138 3029 9565
A B BC A
MMA
FL HL QL
563 535 524
41 55 69
C B AB
63 486 56 325 56 327
3154 5806 7887
BC A A
ST/MMA
FL HL QL
674 683 618
42 70 76
F F DE
82 207 62 737 63 120
7184 8372 9166
D B BC
Control ST
0 FL HL QL
326 481 415 381
25 40 22 30
A E C B
38 898 59490 36 459 41 332
2189 4145 3000 5657
AB C A B
MMA
FL HL QL
500 444 404
47 22 25
E D BC
56 203 39 141 41 512
5739 1896 1675
C AB B
ST/MMA
FL HL QL
547 416 384
24 37 19
F C B
56 439 40 782 38 777
4614 1709 2247
C B AB
Moisture content. Means with the same letter are not significantly different at p < 0.05. Comparisons were done within the each wood species group.
750
40
30 %
25
ST
700
MMA
650 MOR (kg/cm2)
35
MMA/ST
20 15
600 550 500 450
10
400
5
350
0
ST/MMA= -0.0357x 2 + 5.1967x + 511.56 R2 = 0.99
ST = -0.0475x 2 + 4.7313x + 511.84 R2 = 1
MMA = 0.5097x + 511.2 R2 = 0.99
300
100
50 Polymer loading levels(%)
25
0
20 40 60 80 Polymer Loading (%w/w-polymer/od wood)
100
Fig. 5. The percentage increase in MOR of pine–polymer composites.
Fig. 6. Relationship between polymer loading levels and MOR for pine wood polymer.
greatest increase (approximately 25%). Regression analysis (Fig. 10) showed that there was slightly increase as polymer loading level reached 50% for ST/MMA polymer type. Once polymer loading levels of ST/MMA reached 50%, the MOE values increased more obviously. However, for ST, the opposite relationship was observed. In other words, once polymer loading levels of ST reached 50%, MOE values tended to be decrease slightly. In regards to MMA polymer type, until polymer loading levels of MMA reached 50%, there was no increase in MOE; however, once polymer loading
levels of MMA reached 50%, it was observed that there was a slight increase in MOE values. The MOE strength increased from an average of 38 898 kg/cm2 for untreated poplar to an average of 59 490 kg/cm2 for ST impregnated poplar wood polymer samples. The results showed that there were significant differences among the polymer loading levels for ST. However, there was no significant difference between half and quarter loading levels for both MMA and ST/MMA polymer types, but there was significant difference between full loading and half, quarter loading
¨ .C. Yildiz et al. / Bioresource Technology 96 (2005) 1003–1011 U 60 MMA
40
MMA/ST
30 20
70300 MOE (k g/cm2)
%
50
10
60300 50300
MMA = 1.0416x 2 - 26.051x + 55582 R2 = 0.98 2 30300 ST = -2.0759x + 293.6x + 54616 R2 = 0.91 20300 40300
10300 300
0 100
50 Polymer loading levels(%)
25
0
ST/MMA = 2.1771x + 323 R2 = 0.99
MOR (kg/cm2 )
450 400 ST= 1.5074x + 334.8 R2 = 0.98
MMA = 1.6571x + 346 R2 = 0.94
350 300 0
20
40
60
80
100
Polymer Loading (%w /w -polymer/od w ood)
Fig. 8. Relationship between polymer loading levels and MOR for poplar wood polymer.
35
%
ST MMA MMA/ST
20 15 10 5 0
60
80
100
Fig. 10. Relationship between polymer loading levels and MOE for pine wood polymer.
3.1. Fungal decay resistance tests
500
25
40
pine wood samples was limited and there was only slight improvement in all bending strength properties.
600 550
20
Polymer Loading (%w /w -polymer/od w ood)
Fig. 7. The percentage increase in MOR of poplar–polymer composites.
30
MMA/ST = 1.592x 2 + 93.536x + 56526 R2 = 0.95
80300
ST
1009
100
50 Polymer loading levels(%)
25
Weight losses due to fungal attack for pine–polymer and poplar–polymer composites are given in Tables 4 and 5, respectively. The results showed that loading levels regardless of polymer types affected the weight losses of both pine and poplar–polymer composites after exposure to the decay fungi Coniophora puteana and Coriolus versicolor, respectively. The mixture of full loading ST/ MMA gave the best result in terms of decay resistance for both pine and poplar–polymer composites. However, quarter loading of all polymer types did not enhance the decay resistance. Although, in general, poplar wood is more susceptible to fungal decay than pine wood, weight losses of poplar–polymer composites after exposure to the decay fungus Coriolus versicolor were lower comparing to the control poplar wood samples. According to the results, although polymers at full and half loading levels helped decreasing weight losses due to both fungi for each wood species, weight losses were still higher than wood samples treated with chemicals (i.e., copper based or boron wood preservatives). Therefore, it can be concluded that additional fungicide
Fig. 9. The percentage increase in MOE of pine–polymer composites. 35 ST 30
MMA
25 %
levels. The highest percentage increase in MOE for poplar–polymer composites was 30% for full load MMA/ST polymer type (Fig. 11). The lowest percentage increase in MOE were half loading levels for ST. The increasing rates varied between 9% and 30%. Regression analysis (Fig. 12) showed that there was either a slightly decrease or staying constant as their polymer loading levels reached 50% for all polymer types. Once their polymer loading levels reached 50%, the MOE values tended to be slightly increased. Adams et al. (1970) reported that the increase in MOE for MMA impregnated loblolly
MMA/ST
20 15 10 5 0
100
50 Polymer loading levels(%)
25
Fig. 11. The percentage increase in MOE of poplar–polymer composites.
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Table 5 Weight losses of poplar–polymer composites after exposure to the decay fungus Coriolus versicolor for 16 weeks
80300 MMA/ST = 2.6588x 2 - 92.386x + 39042 R2 = 0.99
MOE (kg/cm2)
70300 60300 50300 40300
MMA= 2.6955x 2 - 109.86x + 39901 ST = 4.0995x2 - 223.92x + 40390 R2 = 0.94 20300 R2 = 0.92 10300 30300
300 0
20 40 60 80 Polymer Loading (%w/w-polymer/od wood)
100
Fig. 12. Relationship between polymer loading levels and MOE for poplar wood polymer.
Table 4 Weight losses of pine–polymer composites after exposure to the decay fungus Coniophora puteana for 16 weeks Polymer type
Loading levels
N
% Weight loss
Std. dev.
Homogeneity groupsa
Styrene
FL HL QL 0b
4 4 4 4
16.25 24.50 37.93 34.90
1.96 1.80 7.19 3.66
AB CD F F
MMA
FL HL QL 0b
4 4 4 4
19.80 24.85 31.28 39.10
2.04 3.34 4.38 4.57
BC CD E F
ST/MMA
FL HL QL 0b
4 4 4 4
13.65 20.35 28.45 38.63
4.26 2.18 2.21 3.90
A BC DE F
a Means with the same letter are not significantly different at p < 0.05. b Untreated pine samples (control).
should be added into the polymers if they will be used in ground contact. Yalinkilic et al. (1998) reported that adding boric acid into ST, MMA or ST/MMA lowered the weight losses of Cryptomeria japonica–polymer composites after exposure to decay fungi Tyromyces palustris and Coriolus versicolor for 12 weeks.
4. Conclusions It was observed that all monomers used in this study increased the mechanical strength of the maritime pine wood. Especially, mixture of styrene and methyl methacrylate in which obtained the best results produces WPCs with a price and quality competitive with naturally high-grade woods, and MMA-based WPCs which have a broad spectrum of applications as a construction material. There is a growing shortage of several varieties of wood species in many countries and often a good substitute for a material is not easy to find. A need; therefore,
Polymer type
Loading levels
N
% Weight loss
Std. dev.
Homogeneity groupsa
Styrene
FL HL QL 0b
4 4 4 4
9.67 19.50 24.52 26.23
1.98 2.24 8.11 6.71
A BC C CD
MMA
FL HL QL 0b
4 4 4 4
8.57 15.72 27.17 29.9
1.91 4.64 4.50 9.62
A B C C
ST/MMA
FL HL QL 0b
4 4 4 4
8.05 15.10 25.32 32.70
4.05 10.00 3.79 12.11
A B C CD
a
Means with the same letter are not significantly different at p < 0.05. b Untreated poplar samples (control).
exists for a high-quality, improved low-grade wood which can be used instead of a naturally high-grade wood. Many fast-growing, low density woods like maritime pine can be treated to give high mechanical strength properties to enable their utilization for better purposes.
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¨ .C. Yildiz et al. / Bioresource Technology 96 (2005) 1003–1011 U Lawniczak, V.M., 1973. Effect of moisture content changes on the strength of polystyrene modified wood. Holzforschung Holzverwertung 25 (2), 38–43. Lu, J.Z., Wu, Q., McNabb Jr., H., 2000. Chemical coupling in wood fiber and polymer composites: a review of coupling agents and treatments. Wood Fiber Sci. 32 (1), 88–104. Meyer, J.A., 1981. Wood–polymer materials: state of the art. Wood Science 14 (2), 49–54. Meyer, J.A., 1982. Industrial use of wood–polymer materials: state of the art. Forest Prod. J. 32 (1), 24–29. Rowell, R.M., Konkol, P., 1987. Treatments that enhance physical properties of wood. Gen. Tech. Rep. FPL-GTR-55. USDA Forest Service, Forest Product Laboratory, Madison WI, 32p. Schneider, M.H., 1994. Wood–polymer composites. Wood Fiber Sci. 26 (1), 142–151.
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Schneider, M.H., Phillips, J.G., Tingley, D.A., Brebner, K.I., 1990. Mechanical properties of polymer-impregnated sugar maple. Forest Prod. J. 40 (1), 37–41. Siau, J.F., Davidson, R.W., Meyer, J.A., Skaar, C., 1968. A geometrical model for wood–polymer composites. Wood Sci. 1 (2), 116–128. S ß olpan, D., Gu¨ven, O., 1999. Preservation of beech and spruce wood by allyl alcohol-based copolymers. Radiat. Phys. Chem. 54, 583–591. Yalinkilic, M.K., Tsunoda, K., Takahashi, M., Gezer, E.D., Dwianto, W., Nemoto, H., 1998. Enhancement of biological and physical properties of wood by boric acid–vinyl monomer combination treatment. Holzforshung 52 (6), 667–672. ¨ .C., 1994. Bazı Hızlı Bu¨yu¨yen Ag˘ac¸ Tu¨rlerinden Hazırlanan Yildiz, U ¨ zellikleri, Odun-Polimer Kompozitlerinin Fiziksel ve Mekanik O ¨ Fen Bilimleri Enstitu¨su¨, Trabzon, 296p. Doktora Tezi, KTU
Mechanical properties and decay resistance of wood–polymer composites prepared from fast growing species in Turkey ¨ mit C. Yildiz, Sibel Yildiz, Engin D. Gezer U
*
Department of Forest Industrial Engineering, Faculty of Forestry, Karadeniz Technical University, 61080 Trabzon, Turkey Received 29 September 2003; received in revised form 24 September 2004; accepted 24 September 2004 Available online 11 November 2004
Abstract Some mechanical properties of wood–polymer composites from maritime pine (Pinus pinaster Ait.) and poplar (Populus x. euramericana cv. I-214) wood were investigated. Three different monomers; styrene (ST), methyl methacrylate (MMA) and styrene/ methyl methacrylate (ST/MMA) mixture were used in preparation of wood–polymer composites (WPCs). Full-loading (FL), half-loading (HL) and quarter-loading (QL) were used as polymer content levels. Untreated pine and pine–polymer composite samples were tested in compression strength parallel to grain and static bending strength. WPCs mechanical properties increased compared to untreated wood. The polymer had greater effect on the strengths of the ST/MMA treated pine than on the ST and MMA treated pine samples. Increasing of the mechanical properties should improve the structural competitiveness of WPCs made from fast growing-low density woods. Weight losses due to fungal attack for pine and poplar–polymer composites were also determined. Although polymers at full and half loading levels helped decreasing weight losses due to both fungi for each wood species, weight losses were still found to be higher. 2004 Elsevier Ltd. All rights reserved. Keywords: Wood–polymer composites; Styrene; Methyl methacrylate; Maritime pine
1. Introduction Over the years wood has been treated with a variety of chemicals to change its physical characteristics. From 1930 to 1960 a number of new wood treatments were introduced: acetylation of the hydroxyl groups, ethylene oxide addition to the hydroxyl groups, polyethylene glycol bulking of the cell-wall, the phenol formaldehyde treatments under the name of Impreg and Compreg, and wood–polymer composites (WPCs). WPCs are prepared by impregnating of wood with vinyl monomers * Corresponding author. Address: Engin Derya Gezer, Kafkas University, 08000 Artvin, Turkey. Tel.: +90 535 830 2555; fax: +90 466 212 6951/462 325 7499. E-mail address: [email protected] (E.D. Gezer).
0960-8524/$ - see front matter 2004 Elsevier Ltd. All rights reserved. doi:10.1016/j.biortech.2004.09.010
followed by free radical bulk polymerization in the lumens and cell-walls. By adding bulk vinyl polymers to the void spaces in wood, compression strength, hardness, and abrasion resistance are greatly improved. The diffusion of the water in and out of the WPCs is restricted. WPCs have found commercial application where the specific physical property improvements can be used to advantage. Parquet flooring is a major commercial product. Other commercial items include archery bows, billiard cues, golf clubs, musical instruments, office equipment, and knife handles. With the finish integrated through the WPCs, maintenance problems are kept to a minimum. WPCs are produced in United States, Germany, England, Poland, Italy, Japan, Taiwan, New Zealand and other countries (Meyer, 1982). Several review articles on WPCs have
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been published (Meyer, 1981; Rowell and Konkol, 1987; Schneider, 1994; Kumar, 1994; Lu et al., 2000). From the viewpoint of the method of production of WPCs, the most decisive factor in choosing a suitable wood for raw material is its homogenous impregnability. Hardwoods (deciduous species) have mainly been used in making WPCs. Many woods, including tropical species, have been found useful to make WPCs, such as alder, yellow poplar, ash, maple, walnut, birch, basswood, red gum, beech, red and white pine (Rowell and Konkol, 1987). However, a few studies dealing with the suitability of fast growing wood species have been done (Kumar, 1994; Elvy et al., 1995). The main objectives of this study were (i) to prepare WPCs from maritime pine and poplar as important fast growing wood species in Turkey, (ii) to evaluate the mechanical properties of this pine–polymer composite materials, (iii) to evaluate their decay resistance.
2. Methods 2.1. Wood materials Ten 28-year-old maritime pine (Pinus pinaster Ait.) trees from the original plantation areas in Kerpe Burnu, Kocaeli where is western part of Turkey and ten 9-yearold poplar (Populus x. euramericana cv. I-214) trees from the original plantation areas in Meric, Ipsala where is western border of Turkey were cut down as wood material. were cut down as wood material. Two blocks (each 65 cm long) from the sapwood portion of each log were sawn for mechanical tests. These blocks were airseasoned to equilibrium moisture content prior to preparing of samples. Test and control samples were prepared from these blocks for each mechanical property according to the relating standards. The prepared test and control samples were dried at 103 ± 2 C to determine the oven-dried weights before polymerization (WBP). Test samples were then conditioned until they had 7% moisture content prior to monomer impregnation. 2.2. Monomer solutions Three monomer solutions were used for wood–polymer composite production: styrene (ST), methyl methacrylate (MMA) and styrene/methyl methacrylate (ST/ MMA, 65/28 (w/w) %) mixture containing 2% benzyl peroxide catalyst (polymerization initiator) and 5% divinyl benzene as cross-linker. Monomer solutions were used with the addition of benzene in order to adjust the three different polymer loading levels in WPCs; the full-load level (FL) consisted of 100% monomer solution, the half-load level (HL) 70% monomer solution,
30% benzene, and the quarter-load level (QL) 40% monomer solution, 60% benzene in weight bases. 2.3. Impregnation and polymerization procedure Test samples were placed in a vacuum-chamber and, a full vacuum (<70 mmHg) was drawn on the wood for 30 min. The monomer solutions were introduced into the treatment chamber until the samples were completely covered. The samples were then soaked in monomer solution for 24 h in normal atmosphere and room temperature conditions. The impregnated samples were wrapped in aluminum foil and heated to 90 C for 24 h to polymerize the monomer. After unwrapping, the samples were dried at 103 ± 2 C to remove residual monomer and determine the oven-dried weights after polymerization (WAP). The polymer content (PC) in the test samples was calculated by the formula (Duran and Meyer, 1972): PC% ¼
WAP WBP 100; WBP
where WAP, the oven-dried weights of wood sample after polymerization; WBP, the oven-dried weights of wood sample before polymerization; PC, The polymer content. 2.4. Mechanical tests The following mechanical properties of WPCs and their controls were tested: (i) compression strength parallel to grain with the samples milled to 20 · 20 · 30 mm, (ii) static bending strength with the samples 20 · 20 · 300 mm. Compression and bending tests were performed in accordance with American Society for Testing and Materials 143 (1996). 2.5. Laboratory fungal decay resistance tests Decay resistance was assessed using European Standard EN 113 (1994), with Coniophora puteana for 3 · 2 · 5 cm cut pine wood samples and Coriolus versicolor for 3 · 2 · 5 cm cut poplar wood samples as the test fungi. Four control and four test samples for each group were used. The wood samples and Kolle flasks were sterilized. Each Kolle flask containing malt extract agar was inoculated with an agar disc cut from the actual growing edge of the test fungus and Kolle flasks were incubated at 20 ± 2 C and 65 ± 5% relative humidity until malt extract agar was covered by mycelium. Sterilized test blocks were then placed in the Kolle flask and incubated at 20 ± 2 C and 65 ± 5% relative humidity for 16 weeks. One test wood polymer composite sample and one control were placed inside each Kolle flask. After the incubation period, test blocks were removed and conditioned at 25 ± 2 C and 65 ± 5% relative
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humidity for 2 weeks. Changes between initial and final conditioned weight served as a measure of fungal attack.
3. Results and discussion The polymer content values for pine and poplar obtained in each test samples are given in Table 1. Polymer content for pine and poplar varies greatly among the
1005
polymer loading levels. It was found that the polymer contents for poplar were higher than that of pine because poplar specific gravity is lower than pine. However, there was no significant differences in polymer contents for the same polymer loading levels although wood dimensions were different (i.e. static bending strength wood samples ST and compression strength wood samples ST etc.) for both wood species. It was also found that ST/MMA mixture had slightly higher
Table 1 Polymer content values for pine and poplar of test samples Wood species
Mechanical property
Polymer type
Polymer loading level
Polymer content (in percentage of initial oven-dried weight) Mean
Pine
Compression strength
Static bending strength
Poplar
Compression strength
Static bending strength
a
Std. dev.
Homogeneity groupsa
ST
FL HL QL
111 87 39
6 5 7
AB C E
MMA
FL HL QL
107 69 44
8 5 3
B D E
ST/MMA
FL HL QL
109 91 44
5 5 3
AB C E
ST
FL HL QL
104 88 34
12 6 4
B C E
MMA
FL HL QL
117 84 36
9 9 4
A C E
ST/MMA
FL HL QL
118 98 63
12 9 7
A BC D
ST
FL HL QL
157 88 63
14 22 9
BC F G
MMA
FL HL QL
169 99 45
20 26 13
AB EF H
ST/MMA
FL HL QL
167 136 49
17 28 15
ABC D H
ST
FL HL QL
128 97 50
46 23 17
D EF H
MMA
FL HL QL
158 107 43
20 24 18
BC E H
ST/MMA
FL HL QL
179 140 97
22 33 32
A D EF
Means with the same letter are not significantly different at p < 0.05. Comparisons were done within the each wood species group.
Table 2 Effect of polymer content on compression strength of the pine– polymer composites Wood species
Pine
Poplar
Polymer type
Compression strength, kg/cm2, at 12% MCa Mean
Std. dev.
Homogeneity groupsb
Control ST
0 FL HL QL
378 552 509 413
33 36 34 28
A E D B
MMA
FL HL QL
483 463 419
52 30 33
CD C B
ST/MMA
FL HL QL
625 546 478
57 41 43
F E C
Control ST
0 FL HL QL
278 451 340 352
17 28 22 38
A E B B
FL HL QL
500 377 363
45 25 23
F CD BC
MMA
ST/MMA
a
Polymer loading level
FL HL QL
545 377 399
38 35 38
G CD D
Moisture content. Means with the same letter are not significantly different at p < 0.05. Comparisons were done within the each wood species group. b
90 80 70 60 50 40 30 20 10 0
ST MMA MMA/ST
100
50 Polymer loading levels
25
Fig. 1. The percentage increase in compression strength of pine– polymer composites.
polymer loading levels and compression strength for all polymer types. The data (Table 2) also showed that the highest value in compression strength was observed in ST/MMA poplar samples as 545 kg/cm2, and approximately two times greater than that of untreated. It was determined that there were significant differences between full load and half and quarter loads polymer types; however, there were no significant difference between half loads and quarter loads for all polymer types. Percentage changes in compression strength of poplar–polymer composites are given in Fig. 3. The increasing rates varied between 22% and 107%. The highest rate was obtained in FL level of ST/MMA mixture. The highest rate was obtained in FL level of ST/MMA mixture. This can be attributed to two main reason: the higher polymer content in ST/MMA composite samples and, that ST/MMA mixture has strong branched polymeric situation (Baysal, 1981). The percentage increase in the compression strength compares favorably with the 28–124% reported by different researchers (Autio and Miettinen, 1970; Siau et al., 1968; S ß olpan and Gu¨ven, 1999; Schneider et al., 1990; Kinell and Aagaard, 1969; Lawniczak, 1973). It was reported that the gross wood probably fails in compression due to the buckling of relatively thin cell walls because of a long-column type of instability. The addi-
Compressive Strength (kg/cm2)
polymer content than the others, because the polymerizing rate of this monomer mixture was higher than those of ST and MMA monomers (Yildiz, 1994). The test results relating to the effect of polymer content changes in pine– and poplar–polymer composites on their compression strength parallel to grain determined from 16 repetitions were summarized in Table 2. The highest value in compression strength was observed in ST/MMA pine samples as 625 kg/cm2, and approximately two times greater than that of untreated. It was determined that there were significant differences among the polymer loading levels for all polymer types except MMA half load and MMA full load. It is fairly certain that the compression strength value increases as a result of increase in polymer content. Percentage changes in compression strength of pine–polymer composites are given in Fig. 1. The increasing rates vary between 17% and 75%. The highest rate was obtained in FL level of ST/MMA mixture. In addition, the relationship between polymer loading levels and compression strength for all polymer types and their regression equations for each polymer type were determined (Fig. 2). It was found that there was a linear relationship between
%
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1006
700 650
ST/MMA = 2.3897x + 402.2 R2 = 0.95
600 550 500 450 400
ST = 1.8194x + 383.4 R2 = 0.92
350
MMA = 1.0366x + 390.4 R2 = 0.90
300 0
20 40 60 80 Polymer Loading (%w/w-polymer/od wood)
100
Fig. 2. Relationship between polymer loading levels and compression strength.
¨ .C. Yildiz et al. / Bioresource Technology 96 (2005) 1003–1011 U 120 ST 100
MMA MMA/ST
%
80 60 40 20 0
100
50 Polymer loading levels(%)
25
Fig. 3. The percentage increase in compression strength of poplar– polymer composites.
Compressive Strength (kg/cm 2)
tion of polymer places a coating on the walls which thickens them, greatly increasing their lateral stability (Siau et al., 1968). In addition, the relationship between polymer loading levels and compression strength for all polymer types and their regression equations for each polymer type were determined (Fig. 4). It was observed for poplar wood polymer also that the compression strength value increases as a result of increase in polymer content. However, this situation was not clear between the HL and the QL levels. Table 3 summarizes MOR and MOE for both pine and poplar polymer composites and their controls. The MOR strength increased from an average of 512 kg/cm2 for untreated pine to an average of 683 kg/ cm2 for ST/MMA impregnated pine wood polymer samples. The results showed that there were significant difference among the polymer loading levels for ST. However, there was no significant difference between half and quarter loading level for MMA, but there was significant difference between full loading and half, quarter loading levels. For MMA/ST polymer type, while there was no significant difference between full loading and half loading level, there was significant difference between quarter loading and half, full loading levels. The highest percentage increase in MOR for
600 MMA/ST = 2.4446x + 292.8 R2 = 0.89
550 500 450 400 350 300
MMA = 2.1051x + 287.4 R2 = 0.97
250 200 0
ST = 1.5966x + 285.4 R2 = 0.90
20 40 60 80 Polymer Loading (%w/w-polymer/od wood)
100
Fig. 4. Relationship between polymer loading levels and compression strength.
1007
pine–polymer composites was found to be 32% for half load MMA/ST polymer type (Fig. 5). The lowest percentages increase in MOR were found to be full loading levels for ST and MMA/ST. The increasing rates varied between 9 and 32%. Regression analysis showed that there was a linear relationship between polymer loading levels and MOR for MMA pine wood polymer (Fig. 6). However, for both ST and ST/MMA, there was an increase from 0% to 50% of polymer loading levels. Once polymer loading levels reached 50%, MOR tended to decrease. It can be concluded that the dominant factor is the homogenous distribution of the polymer through the wood structure compare to polymer content level. MOR increased from an average of 326 kg/cm2 for untreated poplar to an average of 547 kg/cm2 for ST/ MMA impregnated poplar wood polymer samples. The results showed that there were significant differences among the polymer loading levels for all polymer types. Percentage increase in static bending strength of the treated samples are given in Fig. 7. The highest percentage increase in MOR for poplar was found in samples impregnated with full load MMS/ST. The increasing rates varied from 10% to 44%. In addition, regression analysis showed that there was a linear relationship between the polymer loading levels and MOR values for all polymer types (Fig. 8). These percentage changes are similar to those changing between 18% and 51% reported by the other investigators (Autio and Miettinen, 1970; Siau et al., 1968; Schneider et al., 1990; Lawniczak, 1973; Brebner et al., 1985, 1988). The wood–polymer composite samples usually failed first in tension on the bottom of the samples and there was no evidence of crushing or gross compression failures. The presence of polymer in the wood had apparently stiffened the thin cell-walls sufficiently to prevent buckling under a compressive load. This probably accounts for the relatively large increases in the static bending strength of the WPCs (Siau et al., 1968; Schneider et al., 1990). The MOE strength increased from an average of 55 303 kg/cm2 for untreated pine to an average of 82 207 kg/cm2 for ST/MMA impregnated pine wood polymer samples. The results showed that there were significant difference between quarter loading level and half, full loading levels for ST monomer. However, there was no significant difference between half and quarter loading level for both MMA and ST/MMA polymer types, but there was significant difference between full loading and half, quarter loading levels. The highest percentage increase in MOE for pine–polymer composites was found to be 24% for full load MMA/ST polymer type (Fig. 9). The lowest percentages increase in MOE were found to be half loading levels for ST monomer. The increasing rates varied between 6% and 24%. Adams et al. (1970) also reported that the MOR for MMA impregnated loblolly pine wood samples showed the
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1008
Table 3 Effect of polymer content on static bending strength of the pine–polymer composites Wood species
Pine
Poplar
a b
Polymer type
Polymer loading level
Static bending strength, kg/cm2, at 12% MCa MOR
Std. dev.
Homogeneity groupsb
MOE
Std. dev.
Homogeneity groupsb
Control ST
0 FL HL QL
512 510 630 600
57 29 43 82
A A E D
55 303 62 988 65 480 58 827
4877 3138 3029 9565
A B BC A
MMA
FL HL QL
563 535 524
41 55 69
C B AB
63 486 56 325 56 327
3154 5806 7887
BC A A
ST/MMA
FL HL QL
674 683 618
42 70 76
F F DE
82 207 62 737 63 120
7184 8372 9166
D B BC
Control ST
0 FL HL QL
326 481 415 381
25 40 22 30
A E C B
38 898 59490 36 459 41 332
2189 4145 3000 5657
AB C A B
MMA
FL HL QL
500 444 404
47 22 25
E D BC
56 203 39 141 41 512
5739 1896 1675
C AB B
ST/MMA
FL HL QL
547 416 384
24 37 19
F C B
56 439 40 782 38 777
4614 1709 2247
C B AB
Moisture content. Means with the same letter are not significantly different at p < 0.05. Comparisons were done within the each wood species group.
750
40
30 %
25
ST
700
MMA
650 MOR (kg/cm2)
35
MMA/ST
20 15
600 550 500 450
10
400
5
350
0
ST/MMA= -0.0357x 2 + 5.1967x + 511.56 R2 = 0.99
ST = -0.0475x 2 + 4.7313x + 511.84 R2 = 1
MMA = 0.5097x + 511.2 R2 = 0.99
300
100
50 Polymer loading levels(%)
25
0
20 40 60 80 Polymer Loading (%w/w-polymer/od wood)
100
Fig. 5. The percentage increase in MOR of pine–polymer composites.
Fig. 6. Relationship between polymer loading levels and MOR for pine wood polymer.
greatest increase (approximately 25%). Regression analysis (Fig. 10) showed that there was slightly increase as polymer loading level reached 50% for ST/MMA polymer type. Once polymer loading levels of ST/MMA reached 50%, the MOE values increased more obviously. However, for ST, the opposite relationship was observed. In other words, once polymer loading levels of ST reached 50%, MOE values tended to be decrease slightly. In regards to MMA polymer type, until polymer loading levels of MMA reached 50%, there was no increase in MOE; however, once polymer loading
levels of MMA reached 50%, it was observed that there was a slight increase in MOE values. The MOE strength increased from an average of 38 898 kg/cm2 for untreated poplar to an average of 59 490 kg/cm2 for ST impregnated poplar wood polymer samples. The results showed that there were significant differences among the polymer loading levels for ST. However, there was no significant difference between half and quarter loading levels for both MMA and ST/MMA polymer types, but there was significant difference between full loading and half, quarter loading
¨ .C. Yildiz et al. / Bioresource Technology 96 (2005) 1003–1011 U 60 MMA
40
MMA/ST
30 20
70300 MOE (k g/cm2)
%
50
10
60300 50300
MMA = 1.0416x 2 - 26.051x + 55582 R2 = 0.98 2 30300 ST = -2.0759x + 293.6x + 54616 R2 = 0.91 20300 40300
10300 300
0 100
50 Polymer loading levels(%)
25
0
ST/MMA = 2.1771x + 323 R2 = 0.99
MOR (kg/cm2 )
450 400 ST= 1.5074x + 334.8 R2 = 0.98
MMA = 1.6571x + 346 R2 = 0.94
350 300 0
20
40
60
80
100
Polymer Loading (%w /w -polymer/od w ood)
Fig. 8. Relationship between polymer loading levels and MOR for poplar wood polymer.
35
%
ST MMA MMA/ST
20 15 10 5 0
60
80
100
Fig. 10. Relationship between polymer loading levels and MOE for pine wood polymer.
3.1. Fungal decay resistance tests
500
25
40
pine wood samples was limited and there was only slight improvement in all bending strength properties.
600 550
20
Polymer Loading (%w /w -polymer/od w ood)
Fig. 7. The percentage increase in MOR of poplar–polymer composites.
30
MMA/ST = 1.592x 2 + 93.536x + 56526 R2 = 0.95
80300
ST
1009
100
50 Polymer loading levels(%)
25
Weight losses due to fungal attack for pine–polymer and poplar–polymer composites are given in Tables 4 and 5, respectively. The results showed that loading levels regardless of polymer types affected the weight losses of both pine and poplar–polymer composites after exposure to the decay fungi Coniophora puteana and Coriolus versicolor, respectively. The mixture of full loading ST/ MMA gave the best result in terms of decay resistance for both pine and poplar–polymer composites. However, quarter loading of all polymer types did not enhance the decay resistance. Although, in general, poplar wood is more susceptible to fungal decay than pine wood, weight losses of poplar–polymer composites after exposure to the decay fungus Coriolus versicolor were lower comparing to the control poplar wood samples. According to the results, although polymers at full and half loading levels helped decreasing weight losses due to both fungi for each wood species, weight losses were still higher than wood samples treated with chemicals (i.e., copper based or boron wood preservatives). Therefore, it can be concluded that additional fungicide
Fig. 9. The percentage increase in MOE of pine–polymer composites. 35 ST 30
MMA
25 %
levels. The highest percentage increase in MOE for poplar–polymer composites was 30% for full load MMA/ST polymer type (Fig. 11). The lowest percentage increase in MOE were half loading levels for ST. The increasing rates varied between 9% and 30%. Regression analysis (Fig. 12) showed that there was either a slightly decrease or staying constant as their polymer loading levels reached 50% for all polymer types. Once their polymer loading levels reached 50%, the MOE values tended to be slightly increased. Adams et al. (1970) reported that the increase in MOE for MMA impregnated loblolly
MMA/ST
20 15 10 5 0
100
50 Polymer loading levels(%)
25
Fig. 11. The percentage increase in MOE of poplar–polymer composites.
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1010
Table 5 Weight losses of poplar–polymer composites after exposure to the decay fungus Coriolus versicolor for 16 weeks
80300 MMA/ST = 2.6588x 2 - 92.386x + 39042 R2 = 0.99
MOE (kg/cm2)
70300 60300 50300 40300
MMA= 2.6955x 2 - 109.86x + 39901 ST = 4.0995x2 - 223.92x + 40390 R2 = 0.94 20300 R2 = 0.92 10300 30300
300 0
20 40 60 80 Polymer Loading (%w/w-polymer/od wood)
100
Fig. 12. Relationship between polymer loading levels and MOE for poplar wood polymer.
Table 4 Weight losses of pine–polymer composites after exposure to the decay fungus Coniophora puteana for 16 weeks Polymer type
Loading levels
N
% Weight loss
Std. dev.
Homogeneity groupsa
Styrene
FL HL QL 0b
4 4 4 4
16.25 24.50 37.93 34.90
1.96 1.80 7.19 3.66
AB CD F F
MMA
FL HL QL 0b
4 4 4 4
19.80 24.85 31.28 39.10
2.04 3.34 4.38 4.57
BC CD E F
ST/MMA
FL HL QL 0b
4 4 4 4
13.65 20.35 28.45 38.63
4.26 2.18 2.21 3.90
A BC DE F
a Means with the same letter are not significantly different at p < 0.05. b Untreated pine samples (control).
should be added into the polymers if they will be used in ground contact. Yalinkilic et al. (1998) reported that adding boric acid into ST, MMA or ST/MMA lowered the weight losses of Cryptomeria japonica–polymer composites after exposure to decay fungi Tyromyces palustris and Coriolus versicolor for 12 weeks.
4. Conclusions It was observed that all monomers used in this study increased the mechanical strength of the maritime pine wood. Especially, mixture of styrene and methyl methacrylate in which obtained the best results produces WPCs with a price and quality competitive with naturally high-grade woods, and MMA-based WPCs which have a broad spectrum of applications as a construction material. There is a growing shortage of several varieties of wood species in many countries and often a good substitute for a material is not easy to find. A need; therefore,
Polymer type
Loading levels
N
% Weight loss
Std. dev.
Homogeneity groupsa
Styrene
FL HL QL 0b
4 4 4 4
9.67 19.50 24.52 26.23
1.98 2.24 8.11 6.71
A BC C CD
MMA
FL HL QL 0b
4 4 4 4
8.57 15.72 27.17 29.9
1.91 4.64 4.50 9.62
A B C C
ST/MMA
FL HL QL 0b
4 4 4 4
8.05 15.10 25.32 32.70
4.05 10.00 3.79 12.11
A B C CD
a
Means with the same letter are not significantly different at p < 0.05. b Untreated poplar samples (control).
exists for a high-quality, improved low-grade wood which can be used instead of a naturally high-grade wood. Many fast-growing, low density woods like maritime pine can be treated to give high mechanical strength properties to enable their utilization for better purposes.
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