Hemp fiber and shives find use in construction industry,particularly in bio-architecture,as raw materials for buildings thermal insulation,due to their physical characteristics.Hemp shives begins to be widely used even in conventional buildings,often mixed with lime or cement to produce thermal insulating conglomerates.Short Technical hemp fiber not meant for textile manufacture is currently quite hard to place on the market,also because of its reduced use in the paper manufacturing field.In buildings it is mainly used to produce thermoacoustic insulating panels or mats,but despite a good variety of hemp products for thermal and acoustic insulation of buildings,in most of the cases hemp is mixed with other synthetic materials and binders that make products not entirely biodegradable; furthermore there is also a lack of self-supporting rigid hemp panels on the market.In Italy one of the main hurdles to hemp cultivation development is due to the lack of suitable machinery to separate fibers from shives,which generates significant production costs,while cost of fibers used in building insulating materials need to be relatively low.Assocanapa and CNR IMAMOTER patented recently a prototype machine for hemp retting and defibering which could make the set up of a local short chain of hemp products of certain interest and more economically effective.FITNESSs is a semi-rigid thermo-acoustic insulating panel made of a composite material,consisting of wool,which partially works as a binder – and hemp fibers.Even after the panel production process the two main components keep their own chemical and physical properties,as they remain separated by a zero thickness thin interface,which makes panels not homogeneous.Nevertheless the hemp fibers addition gives the product a relatively high density if compared with Cartonlana’s,a 100% sheep wool semi-rigid panel realized during a previous research project,and an improved stiffness,marijuana grow system due to hemp fibers tensile strength.
Hemp used for the production of the panels is cut and kept in the field for 4 months to macerate.After maceration,it assumes a gray color and keeps a minimum shives residual,to be considered 1.25% of the weight approximately.Hemp shives is restrained by the fibers and can vary in size between 0.2 and 5 cm in length and 0.05 and 1 cm in thickness.Hemp fibers instead have 10 -70 cm length,but most of the fibers remain in a range between 10 and 20 cm length.Wool comes from Piemonte region sheep breeding; it cannot be used in textile industry,due to its dark color and/or poor quality: fibers are too thick,and irregular length also.Sheep wool is usually washed and dried,but still contains plant debris trapped amongst fibers.As for hemp,treatments on the raw wool are reduced to a minimum,in order to minimize the energy consumption for the production of the panels.Technology assessment has been integrated with the LCA – defined by the UNI EN ISO 14040/44.FITNESs insulation panels have been compared with other experimental products – such as Cartonlana sheep wool panels – and other insulation products already available on the building market,taking into account both thermal performance and environmental impacts.In order to compare the non renewable energy demand of different insulations products,each considered product mass needed to achieve a certain thermal resistance was taken into account.In the LCA study the inventory flows and the environmental burdens were associated to the cultivation of 1 ha of hemp in the regional territory and to a final product which consists in hemp fibers,hemp shives and dust.Authors decided to use an economic allocation based on the current market prices of hemp products and the amount of their annual production.The inventory flows and environmental burdens associated to the sheep wool collection,transport and processing activities was quantified,as described in Bosia et al..Finally,all the input and output flows related to the washed wool and hemp mixture process were studied,in order to assess the potential environmental impacts.All the inventory data for panels production were directly collected from the industrial partners of the research project,and then they were elaborated using the international database Ecoinvent 2.0.
Different insulating building products previously analyzed by the research group with the same LCA methodology and database were considered: Product A is a 100% sheep wool soft mat,product B is a sheep wool and PET semi-rigid panel,product C2 is the 100% sheep wool semi-rigid Cartonlana panel,product D2 is the hemp and sheep wool semi-rigid FITNESs experimental panel.A specific eco-profile,reporting the environmental impacts of 1 kg of product was associated to each product; figure 2 shows the non renewable energy demand needed for each different process unit,considering the process from cradle to gate.Observing the results,product B has the highest primary energy impact,mainly due to Polyester fleece supply,processing and transport from the north Europe.The other three products,100% made of natural materials,require almost the same amount of non-renewable energy.At the beginning of the FITNESs project,the acoustical characterization of sheep-wool and hemp panels was conducted on small samples analyzed by the Kundt’s tube method.The sound absorption coefficient α was established in accordance with EN ISO 10534-2 at the National Institute of Metrological Research.The α values were ascertained by producing standing waves in two tubes with different diameter: 50 mm and 30 mm for measurements in low frequency and high frequency respectively.36 – 46 mm thickness circular samples were placed at the end of the Kundt’s tube during each test.Measurements were recorded at third-octave frequency band within the intervals of 100-5000 Hz and conducted at a air temperature of 22.3 °C,relative humidity of 41.5%,pressure of 99.4 kPa.Further evaluation of the sound absorption coefficient was assessed on finished sheep-wool and hemp panels by means of a reverberation chamber at INRIM.The test specimen was constituted by 12 m2 of stiff panels with thickness 45 mm and density 142 kg/m3,mounted on the floor of the reverberation chamber with the rough side selected as the absorption surface area.Two acoustic tests were carried out: in the 1st test the absorption side of panels was covered with a transparent acoustic fabric,in the 2nd test the measurement was repeated without the fabric.The use of an acoustic fabric to wrap the panels was considered in practical applications of reverberation control to protect absorbent material from damage and especially for aesthetic and hygienic reasons.
According to standard EN ISO 354,the sound absorption coefficient by reverberation chamber method was obtained through two reverberation time measurement sets of the test room with and without the specimen placed in it,within the intervals of 100-5000 Hz in third-octave frequency band.The reverberation room was equipped with diffusing panels to obtain a uniform distribution of acoustic energy and random direction of sound incidence on specimen.Test measurements were conducted at an air temperature of 22.8 °C,relative humidity of 51.7%,pressure of 98.5 kPa.One of the possible ways of achievement of sustainable development in the building industry is moving from the limited and finite material resources to easily renewable raw material resources.A large group of renewable raw materials are materials of plant origin,of which a great importance is attached totechnical hemp like an easily renewable source of cellulosic fibers with potential for reinforcement of composite and non-waste material.Renewal of scientific as well as industrial interests in the use of cellulosic fibres and especially hemp fibres as load bearing constituents in lightweight composite materials relates to a need of progress of environmental friendly products with high use value in term of sustainable development.Nowadays,hemp is regarded to be of important industrial and economic value as a source not only of building materials but of paper,textiles,food,medicine,paint,detergent,varnish,oil,ink,and fuel too.The new research field of hemp fibres utilisation is application such as biodiesel production from hempseed oil and textiles production from hemp stems.Due to low density,biodegrability,interesting thermal,mechanical,acoustic and aseptic properties of hemp fibres,low cost and eco-friendly raw material,this natural fibrous material is used as a replacement of synthetic fibres,such as glass,carbon or metallic fibres.During their growth,cannabis vertical farming harvesting and processing consume overall less fossil energy and chemicals than the synthesis of man-made fibres,their use decreases consequently the carbon dioxide emissions associated with the composite fabrication.
However,one of the major disadvantages of natural fibres is their high moisture sorption sensitivity causing the chemical degradation of the structure of fibres as well as dimensional variations of fibers according to the moisture content and their heterogeneity,which leads to a weak adhesiveness on interface between the fibres and the matrix and to a poor transfer of the applied stress between the materials.This last effect has an impact on the quality of the mechanical interaction between hemp fibres and matrix.The presence of surface impurities and the large amount of hydroxyl groups make plant fibers less attractive for reinforcement of materials too.The surface treatment is necessary in order to optimise the adhesive strength in composites reinforced with natural fibres.The main objective of chemical modification is to remove pectins from the middle lamella in order to separate fibre bundles in fibrils.This fibrillation should lead to an increase the surface area available for chemical bonding between the fibres and the matrix and to appear a more homogeneous surface made of cellulose,which will probably enhance the adhesion between the fibres and the matrix.In this paper,chemical treatment of the surface hemp shives in different environments 2,EDTA-ethylene-diamine-tetra acetic acid at laboratory temperature was performed in order to separate fibre bundles in fibrils and change chemical behaviour or surface state of fibres for their application into lightweight composites.ATR-FTIR and TG were used for identification of changes in the chemical and physico-chemical properties of treated hemp shives in comparison to untreated shives.In recent years,bio-based composite materials have been the focus of academic and industrial research interest from the viewpoint of reducing impact on the natural environment.The use of natural fibers as reinforcement in composite materials is attracting more and more interest from a wide range of industries nowadays.Automotive,construction and packaging companies already use such materials in their products.For high performance composites bast fibers,extracted from the stems of plants such as jute,kenaf,flax,ramie and hemp,are widely accepted as the best candidates due to their very good mechanical properties.Available literature provides the mechanical characterization of natural fibers,in terms of elastic properties and tensile strength;in particular,attention has been focused on different fibers,e.g.flax,jute,hemp,sisal.The reviews report the main mechanical properties of various natural fibers.Hemp especially was shown to have very promising tensile properties for such applications.
The use of natural fibres and in particular hemp fibre bundles as reinforcing agents in composite materials offers many advantages,such as a low density and an enhanced biodegradability,over glass fibres.The technical hemp consists of elementary fibres glued together by an interphase consisting mainly of pectins and hemicelluloses,which are a mixture of different lower molecular weight branched polysaccharides.The inherent difficulty of using natural fibres is due to the fact that their chemical and structural characteristics are complex.Fibres architecture is depicted in Fig.1.The basic unit consists of cellulose polymeric chains aligned and gathered in microfibrils.They are linked to each other by lignin,pectin and hemicellulose.The strength and stiffness of the fibres are provided mostly by hydrogen bonds between the different chemical components.Other characteristics like thermal stability,resistance to UV attack or biodegradation depend on the concentration of each component characterised by its individual properties.Hemicellulose is responsible for the biodegradation,moisture absorption and thermal degradation of the fibres.Lignin and pectin are thermally stable but are responsible for the UV degradation of the fibres.However,the major disadvantage of cellulosic fibres is a high moisture sensitivity,which can cause the chemical degradation of the structure of fibres as well as dimensional variations of the fibres according to the percentage of moisture.This last effect has an impact on the quality of the mechanical interaction between hemp fibres and matrix.Thus,their incorporation in a polymer or mineral matrix implies the overcoming of interface incompatibilities by means of fibres chemical pre-treatments.For these disadvantageous properties of hemp,chemical modification fibres surface is necessary to improve the fiber/matrix interfacial bonding.Many studies are devoted the physical and chemical surface modification of the hemp fibres.It appears that chemical treatment of the fibres surface degrades the amorphous materials present in the fiber structure.As it was shown in >26@,a partial elimination of the amorphous components such as hemicelluloses,lignins and pectins from the surface of hemp fibre bundles by the chemical treatment was realized.During the laboratory study,physical and mechanical properties of composites based on chemically treated hemp shives were compared to referential composite with unmodified hemp shives.In Table 3,bulk density and compressive strength values of 7 days hardened composites are given.Change in thermal conductivity coefficient and water absorbability values composites with chemically modified hemp shives in comparison to referential composite are shown in Table 4.