A new way how shives are used in its native form is in combination with lime for the production of construction materials.Due to the high content of carbohydrates,mostly glucose and xylose ,hemp shives can be considered as a potential source of bio-based chemicals,such as furfural,lactic acid,ethanol,etc.However,due to the compact and rigid structure of hemp shives as all lignocellulosic materials,the selective release of convertible sugars for platform chemicals has become a bottleneck for industrialization of lignocellulosic biorefinery.Based on the results of our previously published study where furfural was obtained from hemp shives,it can be concluded that the lignocellulosic leftover from hydrolysis can be considered as a potential source for other bio-based platform chemicals due to the high content of C6 sugars.It means that this novel hydrolysis technique is a promising stage in the lignocellulosic biorefinery concept.However,there is still a lack of information how hydrolysis time affects the C6 sugars content in the lignocellulosic leftover.In this respect,the present study aimed to analyze the effect of hydrolysis time at different temperatures and amounts of the catalyst on the cellulose content in the hemp shives lignocellulosic leftover.The evaluation of the effect of the same hydrolysis parameters on the yield of furfural was also performed.Based on the obtained data in our previous study,the hemicelluloses after the hydrolysis process at catalyst amounts of 5 % and 7 % in the temperature range of 160–180 ºC were completely removed from hemp shives.Therefore,the carbohydrate content in lignocellulosic leftover was determined in the form of cellulose.Data show that the content of cellulose in the lignocellulosic leftover under the described autohydrolysis conditions increased in the range of 46.6–50.8 %.
The increase of the cellulose content in the lignocellulosic leftover is related to the conversion of hemicelluloses to furfural and other products that were isolated from the reaction medium by the steam.As well,drying cannabis the cellulose are mostly stable up to 180 ºC in the hot water treatment.A similar situation also can be observed also at the hydrolysis temperature of 160 ºC and the catalyst amount of 5 %,wherein the content of cellulose in the lignocellulosic leftover was increased from 47.4 % to 48.0 %.The content of cellulose in the lignocellulosic leftover at a catalyst amount of 7 % and a temperature of 160 ºC was also in the same range.Only this time a small decrease of cellulose was observed with increasing treatment time.Under the above mentioned hydrolysis conditions,a small degradation of cellulose was also observed if the determined content of cellulose was calculated on the theoretically possible amount.Cellulose degraded in the range of 0.3–11.4 %.A further increase of temperature to 180 °C at a catalyst amount of 5% decreased the content of cellulose in the lignocellulosic leftover down to 32.9 %,but at a catalyst amount of 7 % – down to 18.9 %.Hence,the cellulose degradation also increased up to 50.8 % at a catalyst amount of 5 % and up to 74.9 % at a catalyst amount of 7 %.This shows that it is necessary to reduce the hydrolysis time and temperature if the lignocellulosic leftover is intended for the further use.In order to obtain furfural in an amount equivalent to that obtained in common industrial practice ,the used amount of aluminum sulfate octadecahydrate should be higher than 7 % and the steam flow rate should be also changed.Green composites are recently gaining more attention along with raised world’s attention toward the concept of sustainability.Jute,coir,flax,bamboo,and hemp are examples of sustainable materials that are being widely explored by many researchers to substitute synthetic materials.Natural fibers have several promising advantages such as low specific weight,low cost,and the fact that they are biodegradable,non-abrasive and renewable eco-friendly resources.
In addition,their specific mechanical properties are comparable to those of synthetic fibers.Civil engineering is one of the most significant areas for future use of natural fibers as a construction and building material.The first use of natural fibers as a strengthening material was in ancient Egypt about 3,000 years ago where clay was reinforced by straw to form bricks.Various research papers and experiments have proved the effectiveness of using natural fibers in concrete mix design or as a strengthening material against earthquake through concrete confinement.However,the main drawback of these materials is their high variability which leads in return to variability in their physical and mechanical properties.Moisture absorption can lead to dimensional variation in the composites,fiber swelling and eventually rotting due to fungi attack.Moreover,the presence of hydroxyl and other polar groups in natural fibers results in incompatibility between fibers and polymer matrices which leads to a lower interface strength when compared to glass and carbon composites.Among the most used natural fibers as a reinforcement is hemp fiber.Hemp fibers are hydrophilic and absorb moisture where the moisture content of hemp fibers varies between 5 and 10% and may exceed this value.Moisture studies on natural fibers including abaca,jute,hemp,sisal,flax,kenaf,and coir were conducted by Symington et al..Moisture plays an important role in affecting the mechanical properties of natural fibers.While some natural fibers retained their tensile strength when fully soaked at room temperature/humidity conditions,others showed a notable decrease in tensile strength.Thus,durability and expected lifetime are main short-comings of natural fibers when used in structural applications.The foremost objective of this research is to conduct a preliminary study of the durability of natural fibers when used in real-life construction applications,and to investigate their durability performance as well as their behaviour in different environmental exposures.Stress-Strain curves of confined and unconfined cylinders at different rates of W/D cycles are shown in Fig.4.W/D cycles had no effect on the nature of the stress-strain curve.
Concrete confined with hemp-fiber bundles shows similar behavior after W/D cycles in both water and seawater.The stress-strain curve of confined concrete is similar to that of unconfined concrete featuring a post-peak descending branch.The stress-strain response of hemp-fiber confined cylinders shows strain softening indicating low FRP ratio.This can be attributed to the fact that only one layer of hemp fiber is used.Little strength enhancement can be observed in the case of strain softening FRP confined concrete; however,ductility improvement is observed.In fact,the maximum compressive strength is reached before FRP ruptures.Energy absorption is one of the significant deformation characteristics to determine the ductility of concrete structures.Energy absorption is illustrated by the area under the stress-strain curve.Unwrapped specimens subjected to W/D cycles showed insignificant higher energy absorption.This improvement in energy absorption can be attributed to the better performance of concrete when subjected to a prolonged duration of moisture.For all hemp-fiber confined concrete,the stress-strain curves show more toughness,in terms of area,with respect to control cylinders.Fig.5 shows the failure mode of hemp-fiber confined concrete and plain concrete after the different proposed environmental exposures.Visual inspection of wrapped cylinders shows no severe damage with respect to control hemp-fiber confined cylinders.No epoxy deterioration is inspected.Cylinders wrapped with hemp-fiber bundles failed showing fiber rupture with cracking noises before failure.Fiber rupture occurred at different locations along the length of the concrete specimens.About 50% of hemp-fiber confined concrete failed by debonding.A layer of concrete remained attached to the failed hemp-fiber bundles indicating that the bond between concrete and hemp fiber bundles was satisfactory.The unwrapped cylinders failed by concrete crushing and spalling.In general,W/D cycles had no effect on the mode of failure of unwrapped and wrapped cylinders.Regarding the uncoated hemp-fiber bundles,there was no significant difference in tensile strength after 20 W/D cycles using both water and seawater.However,after 40 W/D cycles in water,tensile strength decreased by about 49%,from 132 to 67.5 MPa.Tensile strength was improved by about 28%,from 132 to 169 MPa,after 40 W/D cycles using seawater.After 75 days of prolonged exposure to water,all hemp fibers were completely destroyed and therefore could not be tested.On the contrary,hemp-fiber bundles resisted seawater deterioration where there was no significant change in tensile strength.
The tensile strength of hemp-fiber bundles with epoxy coating was less than the coated ones by about 30%.The tensile strength was 132 MPa and 91.9 MPa in the case of uncoated and coated hemp-fiber bundles,respectively.Poor interfacial adhesion between the fiber and epoxy may be a reason behind this lower tensile strength.Similarly,there was no significant reduction in tensile strength of coated hemp-fiber bundles after 20 W/D cycles.However,a reduction up to 40% was detected after 40 W/D cycles.The tensile strength decreased from 91.9 MPa to 55.4 and 59.1 MPa in water and seawater,respectively.Epoxy coating protected hemp fibers and prevented degradation to a certain extent where tensile strength decreased by about 45% after immersion in water for 75 days,from 91.9 MPa to 51 MPa.Thus,epoxy coating plays a major role in preserving the tensile strength of hemp-fiber bundles.Resistance to seawater degradation was apparent in the conservation of the tensile strength where no significant variation in tensile strength was observed after exposure to seawater.The tensile strength decreased only 13%,from91.9 to 79.8 MPa.Prior to their introduction in the mainstream market,novel materials are commonly installed in small scale self built constructions for demonstration purposes.However,due to the size of the construction market,the atomization of the stakeholders,risks associated with material failure,need for insurance and warranty,along with many other historical and regulatory reasons,the construction sector is a highly regulated environment.Upon the escalation of production,manufacturers need to face the certification of their products.In the process for the introduction of novel materials in the building envelope,designers,manufacturers,installers and final users need to address the characterization and certification of the product performance.The regulatory environment provides many already available product standards which define the suitable testing and certification schemes for already established product categories ,but new products are commonly out of the scope of these standards and lack a recognized procedure for its characterization and certification.In order to address the lack of standardized procedures,these need to be developed,and a consensus reached on their validity within assessment committees,ebb flow commonly on a case-by-case basis.The uncertainty and time requirements for these procedures to be developed are a heavy burden to the development and commercialization of novel materials.In some cases an existing harmonized standard where the product can be placed within its scope,is available.In these cases,performance tests allow for a straightforward way to obtain the CE mark of a product.This label allows for the commercialization of the product in the EU.When such harmonized standards are not available,alternative certification procedures need to be activated.
The most common procedure requires the drafting and approval of a European Assessment Document within the European Organization for Technical Approvals 4,in order to obtain a European Technical Approval.Other alternatives are the declaration product conformity by means of National Assessment Bodies.Generally,these procedures need to be activated for each member states.In some cases,one of such approvals,if correctly targeted at a later use,may pave the way to a CE marking with the previously mentioned EAD+ETA process.All these alternative processes,when compared with CE marking according to harmonized standard,commonly impose a relevant delay in the time to market of construction products.Plants have been largely forgotten by modern technology.Increasingly,however,the bio-economy approach has been targeted as a key element for smart,green growth,with a return to the forefront of annual plants such as hemp,flax and jute.Indeed,the evolution of production and transformation processes ,the need for materials compatible with sustainable construction,consumer expectations for quality products and regulatory requirements are driving manufacturers to turn to resources of biological origin ,which are renewable and have little or even no impact on the environment.Among the different sources of biomass available for further processing,the hemp plant ,referring to industrial hemp,is an environmentally and agriculturally beneficial crop.Hemp differs stands out in comparison to other crops as it is inexpensive,ecological and sustainable,requires neither pesticides nor high volumes of water to grow; it contributes to soil improvement,is carbon neutral,and has low embodied energy consumption.It is also very interesting to note that the whole plant is recoverable for a wide variety of applications.As a multi-use plant,hemp has traditionally been a source of a variety of products,such as cordages,apparel,fabrics,building materials and papers from fibers or flour and oil from seeds.Applications are also found in functional food,beverages,biocomposites ,cosmetics,energy and fuel production,jewelry and fashion sectors.In Europe,hemp production is currently undergoing a renaissance,with France being the largest hemp producer.The hemp plant is cultivated for its fibers from the stalk and its oil from the seeds.The hemp industry also produces by-products called che`nevotte,shives or hurds,which form the inner woody core of the stalks.These by-products,for long considered as wastes,found novel applications in the fields of paper,construction and composites.