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,plant rack for sale 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, 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.Marijuana is the second most commonly smoked substance in our society after tobacco. According to US national surveys, after an initial decline in marijuana use from 1990 through 2005 among adults $ 18 years of age, its use prevalence increased markedly over the following 10 years.This surge in use was most notable among those 40 to 59 years of age, and by 2014 to 2015, 12.9% of all adults reported using marijuana within the last year. More potentially concerning has been the increase in daily or near-daily use from 5.1% to 7.6% over roughly the same time interval among individuals $ 12 years of age.This rise in use prevalence has been accompanied by changing perceptions regarding the risks and benefits of marijuana use that are likely related to the legalization of marijuana for medicinal use by 29 states in the United States and for recreational use in seven states as of 2017. The smoke of marijuana contains many of the same volatile and particulate components found in tobacco smoke, including a variety of chemicals that are injurious to lung tissue, and carcinogens, including benzpyrene and benzanthracene.The major exceptions are nicotine, found only in tobacco, and delta-9 tetrahydrocannabinol , the major psychoactive ingredient, and a number of THC-like compounds, namely cannabinoids, in marijuana.
In view of the similarity in the smoke contents of marijuana and tobacco, the increasing use of marijuana in our society, particularly on a daily or near-daily basis, raises concern regarding a potential link between marijuana smoking and the well-known deleterious effects of regular tobacco smoking on the lung, particularly regarding increased risks for developing COPD and lung cancer. Complicating this public health issue is the observation that most marijuana smokers also smoke tobacco, requiring methods of analysis that control for concomitant tobacco use and examine possible interactive effects and/or restricting the analysis to a comparison of marijuana smokers alone vs nonsmokers of any substance. The aim of this article is to review the evidence mainly from the limited number of publications largely based on observational cohort studies that have systematically addressed these concerns. In addition, findings from case series and other observational studies pertaining to a possible link between marijuana and other forms of lung disease, including pneumothorax/pneumomediastinum, bullous lung disease, and pneumonia risk, will also be reviewed. Although increasing numbers of users of marijuana are adopting other modes of use than smoking , little information concerning the impact of these alternative modes of use on lung health is available. Therefore, the focus of this review will be confined to smoked marijuana.Ten cross-sectional or prospective cohort studies have examined the association between marijuana use and chronic respiratory symptoms after adjusting for tobacco or comparing the marijuana-only users with nonsmokers.The findings are shown in Table 1. Despite the heterogeneity of the populations studied regarding age, amount of marijuana smoked, the presence of concomitant tobacco smoking , and geographic location, the results reveal general, albeit incomplete, agreement regarding a significant association of marijuana use with symptoms of chronic bronchitis.
The notable exceptions were the studies of Tan et al and Morris et al,which included older subjects who may not have smoked as much marijuana as their younger counterparts. In addition, Tan et al appeared to find an interaction between marijuana and tobacco such that the smokers of both substances were more likely to have chronic respiratory symptoms than the smokers of either substance alone. On the other hand, a similar interaction was not reported by other investigators. In addition, one study showed an increased incidence of acute bronchitic episodes over the previous 3 years in habitual marijuana smokers compared with nonsmokers.Somewhat consistent with the latter findings, a large prospective cohort study in Northern California found that a subgroup of 452 frequent marijuana smokers who reported never smoking tobacco had a significantly increased risk of outpatient visits for respiratory illnesses than 450 nonsmoking control subjects.As part of another cohort study in upstate New York, investigators interviewed 749 participants at 14, 16, 22, and 27 years of age and found a significant association of marijuana use with self-reported respiratory problems occurring by their late twenties. However, the analysis was not adjusted for concomitant tobacco use.Two longitudinal studies have shown at least partial resolution of chronic respiratory symptoms in marijuana smokers who quit smoking marijuana.In one of these studies,plant bench indoor resolution of symptoms occurred only in those former marijuana smokers who did not also smoke tobacco.Bronchoscopic studies performed in habitual smokers of marijuana alone , tobacco alone , marijuana plus tobacco , and never smokers provide a clue as to the possible underlying mechanism for the association of marijuana use with chronic bronchitic symptoms.
Bronchial mucosal biopsies revealed widespread histopathologic changes in the bronchial mucosa in marijuana smokers alone that were comparable with those in the tobacco-only smokers, consisting of destruction of the ciliated columnar bronchial epithelial cells and their replacement by mucussecreting surface epithelial cells or reserve cells.An increase in mucus secretion in the face of an impairment in the mucociliary escalator could contribute to cough as an alternative mechanism to cleanse the were performed cross-sectionally at a specified age of the cohort. Results are summarized in Table 2. The studies included both convenience samples of volunteers to advertising and community-based samples in a variety of geographic locations in the United States, Canada, and New Zealand and covered a relatively broad age range. However, several of the studies included predominantly younger subjects. The average amount of marijuana smoked by the self-reported marijuana smokers among the study participants varied widely, but relatively heavy smokers were also represented.In none of these studies was marijuana smoking associated with significant decrements in FEV1 compared with nonsmoking control subjects or after adjustment for concomitant tobacco smoking. In contrast, marijuana smoking was associated with a significant increase in FVC in three of the studies, with a trend toward an increase in an additional study.Marijuana was also associated with a significant decrement in the FEV1/ FVC ratio in three of the studies.However, in one of the latter three studies, the decrease was noted only in the very small sub-population of heavy marijuana smokers with a cumulative lifetime use of > 20 jointyears.Hancox et al have observed an association between marijuana smoking and increases in several subdivisions of lung volume, including total lung capacity, functional residual capacity, and residual volume.
Although the mechanism for the association with increased lung volume is not clear, it has been speculated that it might involve stretching of the lung by the repeated deep inhalations and long breath-holding times that are uniquely characteristic of the smoking topography for marijuana,by analogy with the increased lung volumes that have been observed in swimmers who also take frequent large breaths with long periods of breath-holding during swimming.Furthermore, it has been suggested that the reduced FEV1/FVC ratio observed in some studies could be attributable to an increase in FVC, as opposed to being an indicator of airflow obstruction.In four of the studies in which whole body plethysmography was performed, specific airway conductance was found to be significantly, albeit modestly, decreased among the marijuana smokers.These findings are consistent with the visual evidence of bronchial mucosal edema and increased secretions endoscopically observed by Roth et al among habitual marijuana smokers in large central airways. These bronchial abnormalities likely significantly compromised the airway lumen in a portion of the tracheobronchial tree that represents the major site of resistance in individuals without widespread airflow obstruction. In all four studies in which DLCO was measured, it was not found to be decreased in association with marijuana smoking.Because DLCO is a sensitive but nonspecific indicator of emphysema, these findings argue against an association of marijuana with clinically significant emphysema.In four longitudinal studies, associations between marijuana smoking and changes in lung function over time have been examined.