The intrauterine environment is a determinant for fetal development,and any perturbation that occurs during this critical period of life can predispose individuals to later life diseases.Therefore,more studies are needed to recognize and better understand the impacts of smoking marijuana during pregnancy and its impacts on future health.These aspects and the spreading legalization of recreational use of this drug deserve critical evaluation.Hemp is one of the most productive and useful plants known for a long time,it’s used exclusively for the production of medicines,in the textile field,and also used for the preparation of the drug.However,the transformation of hemp generates a high proportion of waste.Consequently,the development of recycling processes for such wastes present a great interest to the researchers,this waste has integrated the field of composite materials as reinforcing element where he has already been used in composite materials with polypropylene,unsaturated polyester and other composites.Reinforced composites with natural fibers have attracted recently more attention in order to take advantage of their low cost,low density,biodegradability and availability,ease of implementation,their high specific modulus,and ability to be recycled ,etc.These benefits are of interest for applications in various fields such as daily life,automotive …,which require lightweight materials with high performance,opportunities for retraining,the minimum impact on the environment,and reduce the cost of the material.The most serious concerned problem with natural fibers is its hydrophilic nature because they are composed of lignocellulose,cannabis grow facility which contains hydroxyl groups.These fibers are therefore incompatible with hydrophobic thermoplastics,such as polyolefin and have low moisture resistance.
These characteristics are weak points for the uses of vegetable fibers as polymer reinforcements.It is then necessary to improve them so as to avoid penalizing mechanical properties.Another important factor is the dispersion of the fibers for obtaining high mechanical properties.These problems are the main limitations to the use of such fibers as reinforcement in polymers.Thus the matrix fiber interface makes it possible to predict the physicochemical properties of the composite materials; a force applied directly to the matrix on the surface of a composite,is transferred to the nearest fiber and propagates through the fiber at the interface.Incompatible interface,leads to inhomogeneous distribution of the forces which disrupts the mechanical properties of the composites.By cons,a good interface can allow the composite has the ability to withstand stress,even after several fibers are cut because the force can be transferred to non-broken fibers.Several studies have studied the changes cellulose fiber surface properties to enhance their adhesion with a polymer matrix and reduce moisture absorption.It has been shown that an appropriate treatment applied to the fibers may result in compatibility with the polymer matrix,which improves the quality of the composites.Various methods such as plasma treatment,alkali,heat,graft copolymerization,treatment with silane or with other chemicals have improved the compatibility of the fibers with the matrix.It is therefore essential to know the chemical surface interactions between the different constituents of the composites before performing a mechanical characterization of the whole.The main objective of this paper is to study the effect of hemp fibers treatment on their individual properties and their interfacial properties when are mixed with the polyurethane matrix.the improvement of interfacial properties of hemp fibers with the polyurethane matrix,contribute to increasing the composite material properties,the choice of the hemp fibers and the matrix is due to their thermal characteristics tested in this study,this incorporation allows the manufacture of a biodegradable composite insulation.The effect of alkali treatment at different concentration on hemp fibers is shown in the Fig.1a; it is observed that the treatment does not affect the cellulosic structure since characteristic bands of cellulose appear in the same wave number.
The small band due to the C-H bending and C-O stretching of hemicellulose was shifted to a higher wave number indicating the removal of hemicellulose at the surface after treatment.The C-H stretching in aromatic methoxyl group and methylene group of lignin structure begins to disappear while increasing the percentage of NaOH in the solution.Increasing the percentage of NaOH in the solution leads to the removal of an amount of hemicellulose and lignin from the fiber surface,NaOH treatments dissolved a portion of hemicellulose and lignin constituents from the fibers which increases the amount of cellulose exposed on the fiber surface,thereby increasing the number of reaction sites.The FTIR spectra of the fibers treated with silane solution after alkali treatment were presented in Fig.1b It can be observed the appearance of a new absorption bands in the region from 800 to 1800 cm−1,and these are specific to the silane coupling agents.The band at 1203 cm−1 is assigned to the vibrations of Si O-cellulose,indicating that the prehydrolyzed silane has reacted with the hydroxyl groups on the fiber surface.The observed band at 709–780 cm−1,caused by the vibrations of Si O-linkages,indicates that the prehydrolyzed silane has led to self-condensation reactions,giving rise to a siloxane polymer.These results demonstrate that several reactions take place between the silane coupling agents and the fiber surface during the treatment.This is in agreement with the results reported in the literature.Fig.2 shows images obtained on untreated and treated fibers.It can be seen that the untreated fibers have more compounds at the surface.The surface of untreated fibers is covered with fats,waxes or polysaccharides such as the lignin,hemicelluloses or pectins and therefore much rougher.This indicated that hemp fiber structure consists of cellulose microfibrils covered with hemicellulose and lignin.From these micro-graphs it can be seen that the cellulosic fiber surface was covered by non-cellulosic constitute.The treated fibers have a smaller diameter than the untreated fibers and their surface roughness is reduced due to the partial dissolution of the amorphous portions of the fibers.More the percentage treatment increases the fiber surface becomes depleted of non-cellulosic material.
The shows a change in the appearance of the fiber surface which may be due to the formation of silane-coupling agent on the surface of hemp fibers,the fiber surface was completely covered which confirmed the time required to achieve the equilibrium adsorption respected.Natural fibers are semi-crystalline materials composed generally of an amorphous part basically consisting of the macromolecules of lignin and hemicellulose and a crystalline portion of cellulose.The X-ray diffractograms of treated and untreated hemp fibers are indicated in Fig.3,they show the presence of peaks characteristic to cellulose molecule located at,15.2° and 16.6°,correspond respectively to the crystallographic plans 002,101 and 101.The measuring crystallinity index by Segal method presented in Table 1 reveals an improvement of crystallinity rate when the treatment percentage increase,which suggests that the alkali treatment removes non crystalline portion of the fiber increasing the percentage of cellulose in the fiber,this improvement has been observed up to 8% of NaOH treatment,after we have seen a decrease in the crystallinity index,this may be caused by the increased concentration of NaOH affecting the cellulose structure.Other study entrusted the increasing of crystallinity index after the alkaline treatment to the change of the crystalline structure of the cellulose.Studies have shown that Na + has a favourable diameter and is capable to expanding the space between the lattice planes.This leads to the formation of a network cellulose-Na-I,with relatively large distances between the cellulose molecules.The created spaces are filled with water molecules.In this structure,the -OH groups of the cellulose are converted to -ONa groups,widening the dimensions of the molecules.Subsequent washings with water will remove the Na ions bonds and convert the cellulose into a new crystalline structure of cellulose II.Sodium hydroxide allows for complete processing of the cellulose network I cellulose II with a higher crystallinity index.The resistance of the natural fibers is affected by many factors,the high molecular weight of cellulose chains,the crystal structure of the fibers and the microfibrillar angle are the most influences parameters of the mechanical properties of plant fibers.Fig.4a and b show the tensile strength and Young’s modulus respectively of untreated and alkali hemp fibers it can be seen that the treatment increase tensile strength and young’s modulus,this augmentation is observed up to 8% of treatment after this percentage,it is noticed the decrease in mechanical properties of hemp fiber.The increase in mechanical properties is mainly due to the partial removal of hemicellulose and lignin which causes the increase in the crystallinity index of the fibers and therefore the fibers becomes more rigid.The elimination of a certain amount of lignin and hemicellulose allows the relaxation of the microfibrils and their reorganization along the principal axis of the fiber giving rise to a more rigid structure,cannabis grow system the increase in the percentage of NaOH eliminates over amount of lignin and hemicellulose which will create more space empty that the microfibrils reorganizes.
Progressive augmentation of concentration in sodium hydroxide can damage the crystalline structure of the cellulose and therefore has a negative effect on the mechanical properties of the fiber which was observed at 10% of treatment.This behavior has been observed in previous works.The progressive increase in the crystal index of the fibers allows the improvement of the mechanical properties of the fibers,which can increase the mechanical properties of the composite materials after their insertion in a polymer matrix.The alkaline treatment leads to the elimination of a certain amount of impurity and wax on the surface of the hemp fibers which increases the diameter as well as the number of pores on the surface of the fibers and consequently the thermal conductivity increases.The increases of the treatment concentration are accompanied by the increase of the thermal conductivity it has been noticed in another work dealing with oil-palm fibers.The alkali treatment led to a small increase in the value of the thermal conductivity of 13% and 15% for the alkali fibers at 5% and 8% successively after these percentages we notice a strong increase of 24%.Fig.6 show the thermal conductivity of the hemp fibers measured at three temperatures.As the temperature increases,the thermal conductivity of the samples increases because in this case the vibration of the phonons is the thermal carrier and the moisture in the natural fiber begins to evaporate and escapes from the sample.In view of the results obtained,the hemp fibers have a very good conductivity.They can then be used as insulation in cold production or preservation systems in particular compared to polyurethane and polystyrene foam or glass wool which has an average conductivity of 40 mW/m.K.Several experimental techniques are used to predict the mechanical behavior of the fibers after their insertion in composite materials,the fragmentation test,the micro-bond test the push-out test and the pull-out test.These techniques make it possible to calculate the interfacial shear stress IFSS by measuring the maximum force exerted on the fiber in order to extract it from the composite material.Fig.7 shows that pull the fibers from the polyurethane matrix are carried out in three steep.Firstly,the force evolves non-linearly,or it is carried directly by the matrix and transferred from the matrix to the fiber by the fibermatrix interface,during the second stage,the force reaches its maximum and then begins to decrease,this is due to less interpenetration between the matrix and the surface of the fiber,indicating a release of stored energy.This reduction in the tensile force is triggered by the extraction of the fibers from the matrix which takes place after the fracture of the adhesive at the fiber-matrix interface,which makes the fiber detached and starts to slide.Tobacco smoke can cause numerous health related issues.While cigarette smoking is associated with the development of certain respiratory diseases,the causal link between the onset of asthma and smoking has not been established.To date,studies that examined the association between cigarette smoking and incident asthma have shown mixed results.Previous work on the topic has reported an increased risk for adults and adolescents but others reported no statistically significant associations.Although what causes the onset of asthma is still relatively unknown,experts in the field have reported that cigarette smoking or exposure to second hand smoke can certainly trigger asthma symptoms and severity.Overall cigarette smoking or second hand smoke can relate to many long term respiratory health issues,but it can also inflfluence more immediate issues for people with asthma including increased coughing and airway inflammation.For adults in California,cigarette smoking was associated with asthma severity,worse asthma-specific quality of life and greater hospitalization for asthma.Furthermore,active cigarette smoking for people with asthma can lead to accelerated loss of lung function and a decreased response to corticosteroids over time.In the past,studies on smoking behaviour in adolescents was focused on cigarette use; however,more recently other types of smoking such as water pipes,marijuana or now electronic cigarettes have emerged as a concern.