Микология и фитопатология, 2019, T. 53, № 3, стр. 156-161

The decay resistance and durability of wood and wood products from larch (LARIX SIBIRICA)

V. A. Soloviev 1, M. A. Chubinsky 1, A. N. Chubinsky 1, G. S. Varankina 1, A. M. Artemenkov 1*

1 Saint Petersburg State Forest Technical University
St. Petersburg, Russia

* E-mail: a-artemenkov@mail.ru

Поступила в редакцию 8.10.2018
После доработки 13.12.2018
Принята к публикации 24.12.2018

Полный текст (PDF)

Аннотация

The natural resistance is determined and the kinetics of destruction of Siberian larch wood (Larix sibirica) exposed to the wood-destroying fungi Coniophora puteana and Gloeophyllum sepiarium is shown in comparison with pine wood. An assessment was made of the ability to glue veneer from Siberian larch wood. The strength of various types of structural materials from Siberian larch wood has been determined. All the studies were conducted according to well-known standard methods, taking into account the requirements of European standards. It is proved that the natural resistance of larch wood to the action of wood-destroying fungi Coniophora puteana and Gloeophyllum sepiarium is higher than that of pine wood and increases with the age of the tree. The revealed relationship between the location of a sample of wood in the trunk of a tree and its longevity is poorly expressed in comparison with the influence of age and density of wood. The use of Siberian larch wood (Larix sibirica) for the production of plywood and LVL makes it possible to obtain products with increased strength and durability. Glued structures made of Siberian larch wood are also characterized by high durability, strength and water resistance.

Key words: larch, decay resistance, gluing, strength

Larch represents the most common wood species in Russia which reserves amount to more than one third of the total volume of growing stock (about 28 out of 82 billion m3). It has a good physical and mechanical properties as well as natural decay resistance (Table 1) (Bokshchanin, 1982; Chubinsky, 1992; Poluboyarinov et al., 2000; Chubinsky, 2003; Gudaeva, 2004; Neverov et al., 2010; Belyaev, Neverov, 2011; Lavrov, Chakhov, 2014). The properties of Siberian larch wood were the subject of research by foreign scientists (Morrell, Freitag, 1995; Grabner et al., 2002; Koizumi et al., 2003; Gierlinger, Wimmer, 2004; Karlman et al., 2005; Venalainen et al., 2006; Gards, Martinsson, 2007; Martinsson, Lesinski, 2007; Halachan et al., 2017). There were made attempts to cultivate Siberian larch in Scandinavia (Martinsson, Lesinski, 2007).

Table 1.

Physical and mechanical properties of softwood

Species Density, kg/m3 Compressive strength along fibers, MPа Flexural strength, MPа Tensile strength along fibers, MPа Shear strength, MPа Elastic modulus, GPа Decay resistance (loss of wood sample mass, %, by Coniophora puteana)
heartwood sapwood
Larix spp. 640 56.7 98.5 119.5 8.7 13.8
Larix sibirica 660 61.5 97.8 120.5 14.9 23.30 32.15
Pinus spp. 470 39.6 71.8 84.1 6.2 11.9 63.80
Picea spp. 450 39.0 70.3 70.3 6.3 9.3
Abies spp. 380 34.4 60.3 65.6 5.8 8.7

Main larch stand are located in Eastern Siberia and Russian Far East. Larix sibirica and L. dahurica are two main species of larch growing in Russia. Their properties are fundamentally different from those of European larch (L. decidua) in higher rates of strength and impact resistance to wood-destroying fungi (Martinsson, Lesinski, 2007). It is also known that the physical and mechanical properties of wood-based panels of larch depends on many factors (Bokshchanin, 1982; Chubinsky, 1992; Chubinsky et al., 2011; Chausov, Varankina, 2014; Lavrov, Chakhov, 2016), but durability of wood construction depends also on wood decay resistance (Martinsson, Lesinski, 2007). Main reason of the high decay resistance is large amount of wood extractives in larch wood (Chubinsky, 2003).

Despite the large reserves and high mechanical properties, larch is still not enough demand in the production of building materials and structures due to technological difficulties of its treatment. One of the most complex operations are gluing of lumber and veneer from larch wood, where traditionally used urea- and phenol-formaldehyde adhesives (Chubinsky, 1992; Chausov, Varankina, 2014). The surface of the boards of larch wood has poor ability to be wetted by adhesives due to the high content of natural resins.

Due to that, the study of the properties of larch wood and its glue ability, creating full-strength adhesive bonds with the wood is of scientific and practical interest.

MATERIALS AND METHODS

The present study was focused on the following issues: 1) the resistance of Siberian larch wood to wood-destroying fungi Coniophora puteana (Shumach.) P. Karst. and Gloeophyllum sepiarium (Wulfen) P. Karst.; 2) the decay kinetics of Siberian larch wood by Coniophora puteana and Gloeophyllum sepiarium; 3) the gluing ability of Siberian larch wood veneer from Siberian larch wood; 4) Siberian larch wood plywood and LVL strength.

The study of wood decay resistance was carried out by the standard method (GOST 28184-89 “Means of wood protection. The method of determining the limit of exposure to wood-destroying fungi Basidiomycetes class”) taking into account the requirements of European standard EN 350-1 “Durability of wood and wood-based products. Natural durability of solid wood”. Durability was evaluated by weight loss under the influence of wood-destroying fungi Coniophora puteana and Gloeophyllum sepiarium. The decomposition kinetics were investigated by the method of Chubinsky M.A. (Chubinsky, 2003). Another method was proposed by Professor V. A. Soloviev (Soloviev, Malysheva, 2004). Variables in studies of biological stability accepted age of the tree, the position of the sample in the trunk and wood density. A total of 2000 samples were tested with 20 repeats in each experiment.

The gluing ability was determined by known method (Chubinsky, 1992; Lee et al., 2007), by measuring the contact angle. Tests for strength and water resistance of the adhesive bonds were carried out by standard methods (GOST 15613.1-84 “Wood glued massive. Methods for determining the limit of the adhesive bond strength of shearing along the fiber” and GOST 9624-93, 9624-2009 “Laminated glued wood. The shearing method of determining the tensile strength”). A total of 360 samples were tested with 3 repeats in each experiment.

In studies of the gluing ability of wood a traditional domestic urea-formaldehyde and phenol-formaldehyde glue were used.

RESULTS AND DISCUSSION

The properties and structure of the wood depend essentially on the age of the tree, the place of sample situated in tree trunk, density and moisture content. The Figure 1 shows a test results of Siberian larch wood decay resistance, depending on the factors studied.

Fig. 1.

Decay resistance of larch wood.

The average weight loss for the Siberian larch heartwood by exposure to Coniophora puteana was 14.84%, and Gloeophyllum sepiarium – 11.36%, which decreasing with age of the tree (Fig. 2 and Fig. 3).

Fig. 2.

Weight loss depending on the age of larch wood by Gloeophyllum sepiarium.

Fig. 3.

Weight loss depending on the age of larch wood by Coniophora puteana.

A control samples of heartwood pine at age 90 years have demonstrating a weight loss in 57.8% that is significantly higher than the weight loss of larch wood. The age of the tree is one of the most important factors affecting the resistance of wood exposed to wood-destroying fungi. By increasing the age of the tree significantly increase the resistance to the destructive effects of wood-destroying fungi Coniophora puteana and Gloeophyllum sepiarium. The position of samples in the trunk of the tree is also influence by the degree of biological stability, but this dependence is expressed weakly in comparison with the influence of age and wood density.

The studies of the decay kinetics of Siberian larch wood decay (Tables 2, 3) and the role of extractives in the growth of wood-destroying fungi suggest a link to durability and content in the wood extractives, primarily alcoholic extracts.

Table 2.

Kinetics of Siberian larch wood decay by Coniophora puteana

Duration of the experiment, day Weight loss, % Sample moisture content, % Decay kinetics, k, % in days
14 2.5 107.3 0.085
28 3.5 128.3 0.138
56 10.0 161.5 0.323
84 22.3 182.1 0.556
112 38.3 187.5 0.557
140 52.3 206.2 0.357
Table 3.

Kinetics of Siberian larch wood decay by Gloeophyllum sepiarium

Duration of the experiment, day Weight loss, % Sample moisture content, % Decay kinetics, k, % in days
14 2.9 132.8 0.086
28 3.8 146.3 0.118
56 10.0 147.9 0.205
84 18.5 153.1 0.382
112 24.9 157.2 0.399
140 38.6 163.8 0.399

The research results also show a significantly higher moisture samples decayed by Coniophora puteana.

Availability of extractives in larch wood increasing its durability has a negative impact on the ability to interact with adhesives. Larch wood worse wetted by traditionally used in wood processing urea-melamine-formaldehyde (UMF) and phenol-formaldehyde adhesives (PF). Best result is observed while using the special adhesive composition (AC) (Figs 4, 5).

Fig. 4.

Dependence of larch wood wetting ability on its density.

Fig. 5.

The contact angle in dependence on the exposure time after the rotary cut veneer.

However, due to high physical and mechanical properties and the durability of larch wood, derived from it plywood, LVL have improved impact strength and resistance to wood-destroying fungi (Tables 4, 5).

Table 4.

The strength of LVL veneer thickness of 3.0 mm of Siberian larch and pine, Mpa

Type of test Larch Pine
Tensile strength along the fiber 80 65.0
Bending strength perpendicular to surface of sheet 80 58.0
Compression strength along the fibers 78 48.0
Compression across the fibers:
– perpendicular surface 13 8.0
– parallel surface 8 5.7
Strength of glue bond by shearing along the fibers 5 4.3
Table 5.

Resistance of wood materials to Coniophora puteana

Type of material Type of glue Consumption of glue, g/m2 Weight loss, % The standard deviation of weight loss, % The coefficient of variation, %
Larch wood lumber 21.6 3.0 13.8
Pine wood lumber 38.0 4.9 12.8
Pine plywood Phenol-formaldehyde 130 34.9 1.7 4.9
Birch plywood Phenol-formaldehyde 120 43.4 3.5 8.0
Pine gluelum PVA “Kleiberit 303.0” 140 28.5 4.3 15.0
Pine gluelum EPI “Prefere 6151” 350 24.6 3.5 23.6

The shear strength of dry samples of larch plywood on urea-formaldehyde adhesives reaches (1.6–2.0) MPa, and after soaking the samples in water for a day is (1.2–1.5) Mpa that is higher than standard (GOST 3916-96 “Plywood for general purpose”). A high degree performance is achieved also by gluing of larch by veneer phenol-formaldehyde adhesives. Plywood shearing strength in dry state is in the range of (1.9–2.2) MPa and after boiling for hour is not lower than 1.3 MPa.

CONCLUSIONS

The results obtained suggest the following conclusions.

1. The larch wood (Larix sibirica) decay resistance to the attack of wood-destroying fungi Coniophora puteana and Gloeophyllum sepiarium is much higher than pine wood. Decay resistance of wood increases with its age. Position of samples in the trunk of the tree is also influenced by the degree of wood durability, but this dependence is expressed weakly in comparison with the influence of age and wood density.

2. Using of Siberian larch wood for plywood and LVL manufacturing allows to obtain the products of increased strength and durability. The strength of larch veneer LVL exceeds the strength of similar products made from pine by 1.16–1.63 times.

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