thermal conductivity investigation of composite from

Environmental Engineering and Management Journal

September 2015, Vol.14, No. 9, 2213-2220

http://omicron.ch.tuiasi.ro/EEMJ/

“Gheorghe Asachi” Technical University of Iasi, Romania

THERMAL CONDUCTIVITY INVESTIGATION OF COMPOSITE FROM HEMP AND PEAT FIBRES Rūta Stapulionienė, Saulius Vaitkus, Arūnas Kremensas Vilnius Gediminas Technical University, Laboratory of Thermal Insulating Materials, Scientific Institute of Thermal Insulation, Linkmenų st. 28, 08217 Vilnius, Lithuania

Abstract A large number of energy inefficient buildings were constructed without taking into account the principles of green building, which requires efficient utilization of local resources. In this work hemp and peat fibres were used in order to produce effective ecological thermal insulating material. Tests were carried out using short dishevelled hemp and chopped peat fibres. Effective composites from local renewable resources were produced. Macro- and microstructures of composites as well as hemp and peat fibres have shown that activated peat allows getting ecological binder for insulating materials. Hemp and peat fibres are orientated chaotically and fibres consist of many yarns. Investigations have shown that thermal conductivity of natural fibres depends on material density and structure. Key words: composite, hemp fibres, peat, structure, thermal conductivity Received: May, 2014; Revised final: August, 2014; Accepted: August, 2014

1. Introduction Nowadays, one of the most important problems is energy efficiency securing. Increasing energy efficiency of buildings allows not only energy resource to be saved, but also positively affects the indoor climate (Toropovs et al., 2012). Lithuania and other EU members-countries are charged with the implementation of the Directive 2010/31/EU, On Energetic Efficiency of Buildings, adopted by the European Parliament, which imposed that from December 31, 2020 all new buildings should be of zero energy-buildings, which requires the introduction of high standards of energy saving and large use of renewable energy resources (EC Directive, 2010). This aim was raised in order to cut down the EU energetic dependence and gas emission causing the greenhouse effect. Therefore it is important to develop, investigate and use effective and environmentally-friendly thermal insulation materials from local renewable resources. Production 

of such materials and their use for building insulation can reduce both energy cost in material production and building heating (EC Directive, 2010; Vėjelienė, 2012). Studies on the thermal conductivity of building and insulating materials have increased in recent years. New materials are being developed and new uses for existing materials are being found (Ashour et al., 2010). In order to implement the mentioned Directive, it is important to develop, investigate and use effective and ecological thermal insulating materials from local renewable resources. Therefore, it is necessary to produce these thermal insulating materials and to use them for buildings insulation in order to reduce cost of production and mean specific thermal energy consumption. The advantages of natural fibres are:  Natural materials are renewable;  Natural materials are available locally;  The use of natural raw materials in

Author to whom all correspondence should be addressed: e-mail: [email protected]; Phone: +370 5 251 2344

Stapulionienė et al./Environmental Engineering and Management Journal 14 (2015), 9, 2213-2220

production of construction materials greatly reduces the energy demands;  Natural organic materials are easy to recycle (Zach et al., 2010). Insulation materials are increasingly used in the production from renewable resources such as hemp, flax, jute straw, various kinds of wood (Gonzalez-Garcia et al., 2012). Peat is one of the widespread ecological products as well. Thermo-mechanical activation of peat allows for the obtaining of ecological binder for local insulating materials (Toropovs et al., 2012). This paper is focused on the environmental study of hemp and peat as potential sources of fibre from which high quality insulating materials products are produced. According to Ip and Miller (2012), one of the most suitable raw materials is hemp, which has been used as a composite material in a wide variety of products such as insulation, car body components, particulate boards and increasingly in the construction of building envelopes. Textile industry representatives are interested in hemp fibres as well (Jankauskienė et al., 2007). Prade et al. (2011) have studied industrial hemp grown for biogas and solid fuel. The use of hemp biomass for energy purposes has been reported in many countries, e.g. in the USA, Ireland, Spain, Germany and Poland. In Sweden, hemp is already mainly grown for energy purposes. In 2007, hemp was cultivated on approx. 800 ha in Sweden. Most of this biomass was processed into briquettes and sold locally as a solid fuel for private households. Other energy applications such as biogas production by anaerobic digestion (AD) or ethanol production by fermentation from hemp are currently under investigation. Utilisation in combined heat and power (CHP) plants built for combustion of baled straw fuels has also been suggested. According to the researches from Finland (Kymäläinen et al., 2003), short hemp fibres are the most appropriate to use as insulation materials and in packaging materials. However, any industrial utilization of hemp requires the separation of the fibres from the rest of the plant. To separate stem fibres it is necessary to destroy pectins connecting hair bundles with other plant stem tissues. Pectins of hemp stems are decomposed biologically by dew or water retting. After retting other operations begin: breaking and scutching of stalks, hackling of fibres. After processing, short and long fibres are separated (Garcia-Jaldon et al., 1995; Mažonienė and Bendoraitienė, 2008). Hemp is a fast growing annual plant which is cultivated using various methods in different countries, and can be harvested for dual single purposes (for seed and fibre) (Ip and Miller, 2012; Khan et al., 2010). Hemp has large amount of biomass yield (4-6 dry tonne ha-1) and a high percentage of cellulose and lignin. The main chemical compositions of hemp fibres are cellulose (55-72)%, hemicelluloses (7-19) %, lignin (2-5)%

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and pectin (4-8)%. The high biomass and woody structure make it one of the most challenging crops to handle and process in operations such as harvesting, cutting, baling and decorticating for fibres (Khan et al., 2010; Kabir et al., 2013). Scientists investigated the material from hemp fibers, hurds and a binder (fiber with biocomponents), they exhibited low thermal conductivity which varied from 0.0393 W/(m·K) to 0.0486 W/(m·K), when density was from 40.3 kg/m3 to 77.9 kg/m3, respectively (Korjenica et al., 2011). Conducted analysis by Finnish scientists has shown that the thermal insulation materials made from hemp or hemp and flax fibres mixture with the density varying from 25 kg/m3 to 40 kg/m3 have the thermal conductivity 0.050 W/(m·K). Also these scientists have shown that thermal conductivity of loose fill flax fibres varies from 0.045 W/(m·K) to 0.035 W/(m·K) at the densities range from 20 kg/m3 to 100 kg/m3 and hemp fibres from 0.049 W/(m·K) to 0.040 W/(m·K) at the densities range from 25 kg/m3 to 100 kg/m3 (Kymäläinen and Sjöberg, 2008). Zach et al. (2013) have investigated the hemp and polyester fibres composite. They have found out that at variations in densities from 31 kg/m3 to 40 kg/m3 thermal conductivity, respectively, varies from 0.0505 W/(m·K) to 0.0436 W/(m·K), respectively. It is also used as insulating material – board from peat. Širšinaitienė and Puodžiukynas (1995) have investigated that insulation product from peat is characterized by beneficial thermal insulating properties. They have determined the thermal conductivity, which varied from 0.055 W/(m·K) to 0.085 W/(m·K). Latvian researches studied the materials of peat wood composite and peat – hemp composite and they have determined that these composites with the density of 240 kg/m3 have the thermal conductivity ranging from 0.056 W/(m·K) to 0.060 W/(m·K). Peat activation allowed material with properties of a binding agent to be obtained, and they are environmentally safe (Korjakins et al., 2013). Peat loose fibres are made from dried, ground peat with a lime addition (about 5 %) and can be used as loose-fill thermal insulation in floor construction and walls. They are usually blown into the structure in the same way as other loose fill materials (Berge, 2009). According to the British scientists, peat boards are made in thicknesses of 20-170 mm. Their properties such as thermal insulation are very good, and can compete with mineral wool or cellulose fibre. The most widespread method of production begins with the peat being taken to a drying plant where it is mixed in warm water. It is then removed from the water, which is allowed to run off, leaving a moisture content from 87 % to 90 %. The mass is then put into a mould in a drying kiln to dry from 4 % to 5 %. To achieve different densities, different pressures can be applied. The whole process takes about 30 hours (Berge, 2009; Rydin and Jeglum, 2013).

Thermal conductivity investigation of composite from hemp and peat fibres

Peat is a renewable resource, continuing to accumulate on 60 % of global peatlands. However, the volume of global peatlands has been decreasing at a rate of 0.05 % annually owing to harvesting and land development. Many countries evaluate peat resources based on volume or area because the variations in densities and thickness of peat deposits make it difficult to estimate tonnage (Korjakins et al., 2013). The availability of peat as a resource is quite large but very regional. It is a semi-renewable resource, in the sense that new peat is continually but very slowly being formed from decaying vegetation. Extracting peat easily destroys a wetland environment, as well as releasing large quantities of methane CH4, which is a very potent greenhouse gas (Berge, 2009). Peat usually consists of decayed brushwood, plants from marshes, algae and moss. For building, the most important peat is found in the upper light layer of a bog and has not been composted. Older, more compressed and composted peat from deeper in peat bogs can be used in certain circumstances, but it has a much lower insulation value. Totally black, dense peat is unusable (Berge, 2009). Peat moss has baking residues (EriophorumArten) (especially leaves and roots) and growth of plant. Sometimes it is found the reeds (Scheuchzeria) and various species of pine remains. The decomposition degree of peat moss (r index) is from 38% to 51% (LST 1957, 2006). The decomposition degree of peat is the proportion of the matter which has lost its cellular structure due to the decomposition of plant residues. Generally, the decomposition degree of peat is divided into three levels. Lowly decomposed peat is less than 20%, and highly decomposed peat is higher than 40%. When the decomposition degree is between 20% and 40%, the peat is regarded as moderately decomposed (Jinming and Xuehui, 2009). Decomposition of plant tissue is dependent on various factors including temperature, moisture content, oxygen content and residue quality (Dresbøll and Thorup-Kristensen, 2005). The decomposition degree of peat indicates the amount of plant’s residues in peat. It allows to decide about the intended use of peat: more decomposed peat suitable for agriculture, less decomposed peat - the production of compost (Sujetovienė, 2012). Peat has a complex chemical composition, which is determined by the conditions under which peat-forming plants originated, by the chemical composition of the plants, and by the degree of decomposition. By combustible weight, peat consists of 50-60% carbon, 5-6.5% hydrogen, 30-40% oxygen, 1-3% nitrogen, and 0.1-1.5 % (sometimes 2.5 %) sulphur. The organic matter is made up of 1-5% watersoluble substances, 2-10% bitumens, 20-40% readily hydrolyzable compounds, 4-10% cellulose, 15-50% humic acids, and 5-20% lignin (Rydin and Jelgum,

2013). The aim of current work is to develop a rigid composite from local renewable resources, which is characterized by improved thermal insulation properties. 2. Materials and methods In this study, two plants (hemp and peat fibres) were investigated. Hemp fibres were obtained from Lithuanian dried stalks. In order to separate hemp fibres (Fig. 1), hemp stalks were treated by two important processing operations: firstly, hemp plants were processed by the roller machine (primary processing line of hemp), where breaking and scotching were performed; secondly, long hemp fibres were cut into 20-30 mm in length; then, obtained short hemp fibres were dishevelled.

a)

b)

Fig. 1. Hemp fibres: a) treated fibres by the roller machine; b) short dishevelled hemp fibres (20-30 mm)

Peat was obtained from peat bogs in Lithuania. For tests, not fully decomposed peat, i.e. with baking residues (Eriophorum-Arten) (brownish colour of the leaves and roots) and growth of plants with pH ranging from 3.5 to 5.0 was used. Decomposition degree of peat (r index) was from 32 % to 44 %. These raw materials were processed into chopped peat fibres by rotary mill (Fig. 2).

a)

b)

Fig. 2. Peat fibres: a) peat moss; b) chopped peat fibres

After processing of hemp and peat fibres, specimens were formed in order to determine the thermal conductivity dependence on their density

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(Figs. 3 and 4). Three specimens from hemp and peat fibres were formed for thermal conductivity tests.

Fig. 3. Specimen from short dishevelled hemp fibres for thermal conductivity test

was stored in ventilated oven for 24 hours at 70 ºC temperature. Specimens from natural fibres were stored for at least 24 hours at (23±2) ºC temperature and (50±5) % relative humidity conditions. Specimens with dimensions of (300x300x(30÷100)) mm were used for thermal conductivity tests. Thermal conductivity tests of the specimens were carried out in accordance with EN 12667 and EN 12939 requirements. For tests, computerized thermal conductivity apparatus FOX-304 LaserComp was used (Fig. 6). Temperature difference between the measuring plates was 10 ºC. Thermal conductivity was determined by the method of steady-state heat flow at mean temperature of 10 ºC. Each specimen for thermal conductivity measurement was loaded by vertically moving upper plate of device to the fixed thickness of specimen.

Fig. 4. Specimen from chopped peat fibres for thermal conductivity test

Composite was formed from natural fibres (hemp and peat) (Fig. 5). Hemp – peat fibres composite specimen was produced with hemp and peat fibres having a mass ration of 1:1 and certain amount of water which is necessary for the activation of peat fibres.

Fig. 5. Composite specimen made from hemp and peat fibres

Fibred peat mass was stirred in the water and then poured into mixing machine, and stirred until the solid mass was obtained. Activation of peat in the water was used to obtain peat binder. Later on, hemp fibres were poured into mixing machine and further stirred until the solid mass was obtained. Then, the specimen was formed in a metal (300x300) mm mould and compressed in order to remove excess of water. After removal from the mould, the specimen

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Fig. 6. Computerized thermal conductivity apparatus FOX-304 LaserComp

For macrostructure analysis of fibrous materials surface, computerized optical microscope “CMP-USMMICRO10” with a digital camera (which magnifies up to 200 times) was used. Microstructure analysis was performed using scanning electron (SEM) microscope JEOL JSM 7600f, with a maximum magnification of 1 million times and a resolution of 1 nm. For processing of experimental data and evaluation of their reliability, mathematical-statistical methods were used. Such methods provide a fairly accurate assessment of the density and thermal conductivity values, evaluate the scattering of determined values, determine the distribution functions and parameters (Aivazyan, 1968; Williams et al., 1959). For processing of the experimental data, the mathematical-statistical methods as well as the program package “STATISTICA” were used. The mean values of natural fibres thermal conductivity were expressed in term of specimens’ density by the nonlinear relationship by the least squares method. Nonlinear relationships were used for the accurate description of experimental results. Determination coefficient was obtained as well. It is a square correlation coefficient R2 , which indicates the 10 

impact of a particular parameter (in this case, the density) on resulting characteristic (Lakin, 1990).


3. Results and discussion 3.1. Investigation on macro- and microstructures of natural fibres The development of insulating materials from local renewable resources is based on their structure. In Fig. 7 macrostructure of short dishevelled hemp fibres (a) and chopped peat fibres (b) can be observed.

In this study, the structure of the composite from short dishevelled hemp fibres and chopped peat fibres is very relevant. Macrostructure analysis of the composite from natural fibres has shown that the structure of the composite is characterized by chaotic orientation of fibres. Fibres are intermixed and due to this they acquire particular mechanical strength; activated small organic impurities of peat connect fibres into contact zones (Fig. 9a). Performed microstructure analysis of the composite from short dishevelled hemp fibres and chopped peat fibres confirmed that fibres are bound with small organic particles of peat (Fig. 9b).

1 mm

a)

a)

1 mm b)

Fig. 7. Macrostructure of natural fibres: a) short dishevelled hemp fibres; b) chopped peat fibres

We can observe that processed hemp fibres (Fig. 7a) are not as fine as the chopped peat fibres (Fig. 7b), they are more flexible and softer. Hemp fibre is rougher and stronger than the peat fibre, thus, hemp fibres are more difficult to process. Fig. 7b shows that chopped peat fibres particles and air spaces between particles are smaller than those of the short dishevelled hemp fibres. Fig. 7 shows that there are more fibres in chopped peat (in 1 cm2) than in dishevelled hemp. Respectively, it can be stated that the layer of peat fibres is stiffer than the layer of hemp fibres. The microstructure of natural fibres (hemp and peat) is shown in Fig. 8. In Fig. 8a, we can observe that the hemp fibre is large (two times larger than the peat fibre (Fig. 8b) and consists of many yarns. The microstructure of peat fibre shows that the peat fibre is not as fine as expected. Small organic impurities of peat, which are useful in order to activate peat fibre and bind these two fibres at a certain temperature, can be also observed.

b)

Fig. 8. Microstructure of natural fibres: a) short dishevelled hemp fibres; b) chopped peat fibres

The bonds consisting of fibres and small organic impurities form practically only in intermixed fibrous zones at the certain temperature, because natural fibres are covered with small organic impurities, which do not penetrate into fibres, but are “trapped” on the surface of dishevelled fibres. 3.2. Investigation of thermal conductivity One of the main parameters that define the structure of the thermal insulating material is the apparent density. Density is a key indicator that describes the thermal conductivity. Whereas, two types of materials – hemp and peat fibres – have been chosen; thermal conductivity dependences of specimens from hemp and peat fibres on density were analyzed.

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Thermal conductivity, W/(m·K)

0.064 0.060 0.056 0.052 0.048 0.044

1 mm

35

40

45

50

55

60

65

70

3

Density, kg/m

a)

Fig. 10. Relationship between thermal conductivity and density of specimens from dishevelled hemp fibres

In hemp of thermal conductivity measure is approximated by regression equation (Fig. 10) (Eq. 2), with mean square deviation S r  0.00124 and determination coefficient R2    0.789 , which 10 C

shows that the variation of hemp 10C value depends by 97 % on density of hemp specimens and only by 3 % on other factors. The equation is only valid for specimens with densities ranging from 40.4 kg/m3 to 67.3 kg/m3.

Fig. 9. Macro- and microstructures of composite from natural fibres: a) macrostructure of composite; b) microstructure of composite

Densities of specimens from hemp and peat fibres varied from 40 kg/m3 to 67 kg/m3. Fig. 10 and Fig. 11 present the relationship of experimental data for hemp and peat fibres specimens between the thermal conductivity and density. In the performed investigations, the type of relationship between variables (thermal conductivity at mean temperature 10 °C – density of hemp and peat fibres) was approximated by the regression equation (1):

10C  b0  b1    where: 10C is

b2

(1)



thermal

conductivity

at

1.690

(2)





Thermal conductivity values of specimens from peat fibres is approximated from 0.0440 W/(m·K) to 0.0379 W/(m·K), when the density ranges from 41.2 kg/m3 to 68.2 kg/m3 (Fig. 11). 0.044 0.042 0.040 0.038 0.036 0.034

mean

temperature of measurement 10 °C, W/(m·K); b0 , b1 , b2 -constant coefficients calculated according to experimental data by last-squares method (Aivazyan, 1968; Lakin, 1990);  -density of hemp and peat fibres specimens, kg/m3. Fig. 10 shows that thermal conductivity of specimens from hemp fibres decreases with the increase in density. Thermal conductivity values of specimens from hemp fibres is approximated from 0.0475 W/(m·K) to 0.0430 W/(m·K), when the density ranges 40.4 kg/m3 to 67.3 kg/m3, respectively.

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10 C  0.0109  0.000172   

Thermal conductivity, W/(m·K)

b)

35

40

45

50

55

60

65

70

Density, kg/m3

Fig. 11. Relationship between thermal conductivity and density of specimens from chopped peat fibres

The peat fibres of thermal conductivity values are approximated by the regression equation (3) (Fig. 11), with mean square deviation and determination coefficient S r  0.00120 2 . R   0.970 1.564 (3) 10 C  0.0103  0.000354     10 C


Thermal conductivity, W/(m ·K)

The equation is only valid for specimens with densities ranging from 41.2 kg/m3 to 68.2 kg/m3. Analysis of experimental data shows, that at the same density thermal conductivity of hemp and peat fibres specimens differs significantly. When density of hemp and peat fibres specimens is 42 kg/m3, thermal conductivity coefficient differs 39.6%, at the density of 65 kg/m3 difference is 30.9 %. The determined regression dependencies of hemp and peat fibres of thermal conductivity on density may be used for inspection of production of fibres and compliance of finished products. Our analysis has shown that the material density has a significant impact on thermal conductivity. Experimental studies have shown that thermal conductivity of specimens from hemp and peat fibres decrease with the increase in specimens’ density. When the density of specimens from hemp fibres reaches about 67.3 kg/m3, the thermal conductivity value decreases. While the lowest thermal conductivity of specimens from peat fibres is obtained, when the density is about 65 kg/m3. This can be explained by the fact that hemp fibres with such density are not fully compressed. There is a high amount of air spaces and solid phase in the specimen from hemp fibres. While specimens from chopped peat fibres are compressed enough and have a rigid carcass. Peat fibres are finer and their amount is higher in 1 cm2 than the amount of hemp fibres. A composite material from hemp and peat fibres was produced based on the obtained results. Thermal conductivity dependence on the density of material can be seen in Fig. 12.

0.0481

0.0461

0.0436

173

179 Density,

186

kg/m 3

Fig. 12. Natural fibres composite relationship between thermal conductivity and density of specimens from chopped peat fibres

Fig. 12 shows that thermal conductivity of the composite from hemp and peat fibres has changed by 5.4 % with the increase in density (from 173 kg/m3 to 179 kg/m3). While thermal conductivity of the composite has changed by 10.3 % with the increase in density (from 173 kg/m3 to 186 kg/m3). The thermal conductivity of the obtained composite from natural fibres depends on its density and structure. The values of thermal conductivity

have decreased proportionally to the increase in density. Facing the reduction in minerals resources and the threat of global climate change, the reduction of energy consumption has become the main strategy of the survival. Selection of the “green” building makes it possible to save the energy. Energy is used in various stages of building materials production and exploitation: starting with the extraction and transportation of raw materials, heating and lighting of plants, transportation of products to the destination, building maintenance and, finally, demolition of the building at the end of its lifecycle. Analysis of literature has shown that natural fibres are characterized by good thermal properties; therefore, sufficiently effective thermal insulating materials can be obtained. The comparison of the results obtained by Finnish scientists (Kymäläinen et al., 2008) and us has shown that the values of thermal conductivity and density of specimens from natural fibres differ only slightly. Zach et al. (2013) produced a composite from hemp and polyester fibres with the density varying from 31 kg/m3 to 40 kg/m3 and thermal conductivity ranging from 0.0505 W/(m·K) to 0.0436 W/(m·K), respectively. The scientists Širšinaitienė and Puodžiukynas (1995) have obtained, that the thermal conductivity of the composite from peat ranged from 0.055 W/(m·K) to 0.085 W/(m·K). Latvian researches (Korjakins et al., 2013) have obtained the composite from hemp and peat granules with the thermal conductivity ranging from 0.056 W/(m·K) to 0.060 W/(m·K) and the density of 240 kg/m3. Produced composite from hemp and peat fibres had a density varying from 173 kg/m3 to 186 kg/m3 and thermal conductivity ranging from 0.0436 W/(m·K) to 0.0481 W/(m·K), respectively. Comparing our and other scientists’ results of the thermal conductivity, it can be stated that our composite from natural fibres is characterized by satisfactorily thermal insulating properties and can be used as an effective ecological thermal insulating material for building envelopes. 4. Conclusions 1. Experimental investigation has shown that natural fibres has low thermal conductivity and may be used as loose-fill thermal insulating materials as well as in production of effective and ecological thermal insulating composites. 2. Based on the experimental data, a relationship between hemp and peat thermal conductivity and density is determined. The empirical equations developed in our work allow the impact of density on thermal conductivity to be predicted. 3. An effective thermal insulating composite from properly processed hemp and peat fibres was developed. It has a density ranging from 173 kg/m3 to 186 kg/m3 and thermal conductivity varying from 0.0436 W/(m·K) to 0.0481 W/(m·K), respectively.

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4. Macro- and microstructures studies have shown that fibres are situated chaotically, thus forming fine pores, which are useful for thermal conductivity since increasing material porosity reduces heat loss through the solid carcass. 5. Such composite materials from natural fibres are prospective due to renewable and ecological resources usage in their production. The production of these composites requires low energy consumption and CO2 emission. 6. These materials from renewable resources require low energy consumption for utilization at the end of their lifecycle. Acknowledgements This work has been supported by the Research Council of Lithuania (Project, No. ATE-07/2012).

References Aivazyan S.A., (1968), Statistical Analysis of Dependencies, Application of Correlation and Regression Analyses and Processing of Experimental Results, Menallurgy, Moscow. Ashour T., Wieland H., Georg H., Bockisch F.-J., Wei W., (2010), The influence of natural reinforcement fibres on insulation values of earth plaster for straw bale buildings, Materials and Design, 31, 4676-4685. Berge B., (2009), The Ecology of Building Material, Oxford, Elsevier, Amsterdam. Dresbøll D.B., Thorup-Kristensen K., (2005), Structural differences in wheat (Triticum aestivum), hemp (Cannabis sativa) and Miscanthus (Miscanthus ogiformis) affect the quality and stability of plant based compost, Scientia Horticulturae, 107, 81–89. EC Directive, (2010), Directive 2010/31/EC of the Energy Performance of Buildings, Official Journal of the European Union, L153, 13-35. EN 12667, (2001), Thermal performance of building materials and products - Determination of thermal resistance by means of guarded hot plate and heat flow meter methods - Products of high and medium thermal resistance, Lithuanian Standard Board Vilnius, Lithuania. EN 12939, (2000), Thermal performance of building materials and products - Determination of thermal resistance by means of guarded hot plate and heat flow meter methods - Thick products of high and medium thermal resistance, Lithuanian Standard Board, Vilnius, Lithuania. Garcia-Jaldon C., Dupeyre D., Vignon M.R., (1995), Fibres from semi-retted hemp bundles by steam explosion treatment, Biomass and Bioenergy, 14, 251-260. Gonzalez-Garcia S., Luo L., Moreira M., Feijoo G., Huppes G., (2012), Life cycle assessment of hemp hurds use in second generation ethanol production, Biomass and Bioenergy, 36, 268-279. Ip K., Miller A., (2012), Life cycle greenhouse gas emissions of hemp–lime wall constructions in the UK, Resources, Conservation and Recycling, 69, 1–9. Jankauskienė Z., Gruzdevienė E., Endriukaitis A., (2007), Cultivation technology of hemp (Cannabis Sativa) (Lithuanian), Lithuanian Institute of Agriculture, Kaunas, Lithuania. Jinming H., Xuehui M., (2009), Coal, oil shale, natural bitumen, heavy oil and peat, UNESCO, EOLSS Publishers, Oxford, UK.

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Kabir M.M., Wang H., Lau K.T., Cardona F., (2013), Effects of chemical treatments on hemp fibre structure, Applied Surface Science, 276, 13–23. Khan Md. M.R., Chen Y., Lague C., Landry H., Peng Q., Zhong W., (2010), Compressive properties of Hemp (Cannabis sativa L.) stalks, Biosystems Engineering, 106, 315-323. Korjakins A., Toropovs N., Kara P., Upeniece L., Shakhmenko G., (2013), Application of peat, wood processing and agricultural industry by-products the insulating building materials, Journal of Sustainable Architecture and Civil Engineering, 1, 62-68. Korjenic A., Petránek V., Zach J., Hroudová J., (2011), Development and performance evaluation of natural thermal-insulation materials composed of renewable resources, Energy and Buildings Volume, 43, 25182523. Kymäläinen H.-R., Koivula M., Kuisma R., Sjöberg A.-M., Pehkonen A., (2004), Technologically indicative properties of straw fractions of flax, linseed (Linum usitatissimum L.) and fibre hemp (Cannabis sativa L.), Bioresource Technology, 94, 57–63. Kymäläinen H.-R., Sjöberg A.-M., (2008), Flax and hemp fibres as raw materials for thermal insulations, Building and Environment, 43, 1261-1269. Lakin G.F., (1990), Biometry, Vyshaya Shkole, Moscow, Rusia. LST 1957, (2006), Peats and peatproducts for agriculture and landscape gardening – Test methods, properties, specifications, Lithuanian Standard Board, Vilnius, Lithuania. Mažonienė E., Bendoraitienė J., (2008), Fibres, Lithuanian University of Educational Sciences, Vilnius, Lithuania. Prade T., Svensson S-E., Andersson A., Mattsson J.E., (2011), Biomass and energy yield of industrial hemp grown for biogas and solid fuel, Biomass and bioenergy, 35, 3040-3049. Rydin H., Jeglum J.K., (2013), The Biology of Peatlands, Oxford Universitety Press, London. Širšinaitė K., Puodžiukynas R., (1995), Thermal insulating materials, method of production and the use, Lithuania Patent No. 3438. Sujetovienė G., (2012), APL 3003 Ecology of Soil, Practical Works, Vytautas Magnus University, Kaunas. Lithuania. Toropovs N., Korjakins A., Shakhmenko G., Kara P., (2012), Granulated ecological thermal insulation material based on peat binder, In: Riga Technical University 53rd International Scientific Conference: Latvia, Riga, 11-12, 390-390. Vėjelienė J., (2012), Impact of technological factors on the structure and properties of thermal insulation materials from renewable resources, PhD Thesis, Vilnius Gediminas Technical University, Vilnius, Lithuania. Williams E.J., Wiley J., Sydney S., (1959), Regression Analysis, New York, London. Zach J., Brožovský J., Hroudová J., (2010), Research and Development of Thermal-Insulating Materials Based on Natural Fibres, The 10th International Conference on Modern building materials structures and techniques, Vilnius, Lithuania. Zach J., Hroudova J., Brožovsky J., Krejza Z., Gailius A., (2013), Development of thermal materials on natural base for thermal insulation systems, Procedia Engineering, 57, 1288-1294.