Among the 4 harvested industrial hemp products, diesel fuel consumption and fertilizer were the inputs that were most affected in the field subsystem and together ranged from 73 and 82% of the total impacts, while machinery upstream manufacturing accounted for a minor proportion of the requirements . These results were also confirmed by Zampori et al. who found that fertilization is one of the main impacting processes in industrial hemp cultivation and harvest. Another energy and environmental aspect to emphasize is related to irrigation water. The cultivation of industrial hemp in Mediterranean climates, with low rainfall during the growing season, causes irrigation practices to be a fundamental requirement. This practice was included in this study, where the water sources at both experimental sites came from pressurized irrigation networks with negligible direct energy requirements. Moreover, as already stated, industrial hemp cultivation in southern Mediterranean conditions requires higher irrigation volumes, in contrast to northern environments, but has lower water requirements than other specialized crops, such as maize, that are commonly utilized in ADPs. The industrial hemp seed oils that were obtained from plants cultivated in contaminated soil can be used for nonfood products, such as oil, to revive fine furniture woods and in the biodiesel industry. In fact, biodiesel is one of the most commonly accepted complementary fuels for diesel engines, where in recent years, the cost and competition with the food sector have been decreased by using nonedible feedstock . Another application of nonedible oil has been proven by QuilesCarrillo et al., who discussed the use of maleinized industrial hemp seed oil to reduce the intrinsic brittleness of polylactide materials without compromising their mechanical resistance and to construct toughened biopolymer pieces, plant benches which can find interesting applications in, for instance, rigid packaging.
The AD subsystem allowed us to explore the energy and environmental benefits of using the industrial hemp biomass that was obtained from contaminated soil for biogas production while avoiding secondary pollution. The digestates were modeled to be dewatered by using the heat from the CHP unit and then incinerated in a BFPP for electricity production. This solution, because of the reduction in the biomass to be disposed of in authorized plants, enables us to reduce the disposal costs and to obtain energy from renewable sources. To the authors’ knowledge, the use of industrial hemp as feedstock for ADP has been well discussed in the scientific literature; in contrast, the use of HM-contaminated industrial hemp biomass as feedstock for ADPs is absent. A recent review indicated that industrial hemp biomass is a suitable crop for AD applications with high biogas production yields. Plants that are obtained in the phytostabilization of trace element-contaminated soil may affect biomass biodegradability, while HMs affect the physiological and biotechnological environments in AD. In fact, HMs interact with the microbial community and affect biogas production in AD processes, where trace HMs can promote biogas and methane production, while excessive HMs cause inhibition. Lee et al.demonstrated that the inhibition derived from HM-contaminated biomass was negligible, consequently, AD seems to be feasible for the disposal of HM-containing crop residues from phytoremediation sites. However, the release characteristics and fates of HMs should be carefully considered to predict the stability of the AD process for HM-containing biomass. Regarding BFPPs, greater energy and environmental benefits might be achieved by using the waste heat that is generated by these plants. As reported by BEN, most of the heat derived from cogeneration plants is used in the same facilities, while a minor proportion is used in district heating networks to provide heating services to the domestic sector. Instead of dispersing the waste heat that is generated by thermoelectric power plants into the atmosphere, these plants might convey this heat for useful consumption, which would thus avoid burning fossil fuels that would otherwise be necessary to be consumed to provide the same heating service.
The disposal of biomass ash represents a point of debate in environmental studies. The ash yields from biomass combustion range from 0.4 to 6%, and the ash compositions vary depending on the nature of the incinerated biomass. For this reason, it is important to individually characterize each type of biomass ash prior to finding an appropriate utilization approach. Biomass ash disposal has been found to be an influencing factor in the bioenergy and biowaste supply chain, while other studies have found that the contributions of the final disposal of biomass ash were not significant or were excluded from the study boundaries. Biomass ash is free of nitrogen and contains large amounts of micro- and macronutrients that are highly suitable for mineral soil amendments, the biological reclamation of degraded areas and dewatering sewage sludge. In addition, a recent review by Cui et al. emphasized that the incineration of contaminated biomass in modern incineration systems represents a technologically and economically feasible approach for treating hyperaccumulator plants, where ash residues could be pretreated and employed to produce construction materials and high-density glass-ceramics. Modern incineration systems could employ environmentally sound technologies that would perform better than pyrolysis and gasification-melting plants because of several benefits of flue gas cleaning, ash recycling, and the combined heat and power cycle. Moreover, these authors found that the efficient management of metals and bottom ash may decrease the volumes of waste landfills and reduce the consumption of raw materials. Finally, these results identify the great potential of using contaminated areas for bioenergy production while minimizing the exploitation of natural resources and avoiding pollutant emissions into the environment. As suggested by Pulighe et al. , the cultivation of marginal lands for bioenergy production provides ample opportunities to conduct successful feedstock production in unmanaged areas. Currently, HM contaminated soils are mostly unproductive and require expensive and long-term remediation programs to be turned into productive areas . Recently, the use of natural fibers has increased considerably due to its availability, low-density and price compared to synthetic fibers. Those factors are responsible for the apparition of a new polymer science and engineering research.
Natural fibers were introduced with the intention of yielding lighter composites, coupled with lower costs, compared to the fiber glass reinforced polymer composites. Natural fibers have a lower density than that of glass fiber , which ensures the production of lighter composites. Conventional petroleum based epoxy resin, polyurethane , are used extensively with natural fibers, such as hemp, jute, sisal, and kenaf.Recently, the rapidly expanding use of composite components in construction, sports, leisure, and other mass production industries, has been focused on sustainable and renewable reinforced composites. Building insulation is one of the most applications of this material, mechanical and thermal properties are the obvious needs in this area. Physical properties of polyurethane-based composites have been widely studied. Hadjadj et al. demonstrated that Young’s modulus of PU-Alfa fibers composite improved linearly with the embedded cellulose content, it increase by 250%–700% when the fiber reinforcement is raised from 5% to 30%. Radzi et al. have also studied the influence of the addition of Roselle fiber on the mechanical and thermal properties of polyurethane composites they concluded that the tensile and fluxal strength increase with fiber contents, 40 wt% fiber content showed the highest strength. Oushabi et al. studied the effect of polyurethane reinforced by date palm waste, they showed that this reinforcement affects the mechanical properties of the resulting composite, the thermal conductivity of prepared composite makes it possible to consider them as competitive for the development of effective, inexpensive insulating materials and safe. Silva et al. studied the influence of Eucalyptus grandis fibers on rigid PUs and found that the addition of 16% natural fiber drastically increased their mechanical strength and thermal conductivity. Hemp fiber is one of important natural fibers used in industrial areas, which has relatively short cropping cycle and can be easily grown in a large array of environments. In addition, hemp characterized by a tensile strength of up to 1110 MPa is one of the strongest fibers among all bast fibers. There are previous studies reporting on mechanical properties of PU-hemp fibers composites they concluded that treated hemp fibers with alkaline, silane or acetyl solutions can improve tensile and flexural properties of composites. Several works are interested in the mechanical behavior of polyurethane- natural fiber composites, but few have studied the effect of this reinforcement on the thermal conductivity. The aim of this paper is to study the properties of hemp fiber reinforced composites with differential fiber contents . Mechanical, hygroscopic and thermal conductivity, of HF/PU composites were examined.
During their life cycle service, rolling bench the composites materials are often exposed, for long periods, to humid environments. However, moisture generates heterogeneous internal stress fields in this type of material, which leads to the changes in thermal and mechanical properties. Thus, it is interesting to predict the absorption of water for all formulations in order to estimate their sustainability. Water uptake effects on thermal conductivity have been studied by they reported that the thermal conductivity of composite materials increases with volumetric water content. The origin of this increase is due to the saturation in water, in this state the water occupies the open pores of the materials.The water uptake can also affect the mechanical properties of composite materials; the water molecules change the structure and properties of the fibers, matrix and the interface between them, leading to the loss of compatibilization between the fibers and the matrix, to the chain reorientation and shrinkage of matrix also lead to the degradation of natural fibers by a hydrolysis mechanism. All these factors led to decrease mechanical properties of the composite. The water absorption amount was calculated by the weight difference between the samples exposed to water and the dried samples using the following Eq1. Water absorbed percentages in terms of a time for all samples are showed in Fig. 6. The same behavior was observed for all samples, composite materials absorbed water in two stages, and during the first stage the speed of absorption is very fast reaching a certain value, then slows and approaches saturation after prolonged time following a Fickian diffusion process. Both the initial rate of water absorption and the maximum water uptake increase for all hemp fiber composites samples as the fiber content increases. From sorption, diffusion and permeability coefficients values shown in Table 2 it is clear that the polyurethane absorbs less distilled water than prepared composites due to its closed cell structure which prevents water absorption and moisture storage. The incorporation of hemp fibers, highly hydrophilic, increase greatly the water content that can be retained by the composite materials, this behavior has been observed in other works of hemp fibers and polymer matrix composites. Water absorption increase at higher fiber content, the composite PU 30%, has the largest water uptake and permeability coefficient, which limits the use of these renewable resources to high percentages exceeding 25%.The performance of materials is always presented in terms of their mechanical characteristics, such as tensile properties, flexural properties, compression properties, impact properties and wear behavior. It is evident from Fig. 7 that all composites showed a ductile behavior, The properties of the polyurethanes vary considerably with the fiber content, reinforced composites with hemp fibers showed better tensile strength than the polymer matrix. The tensile strength of composites has been found to increase with hemp fibers reinforcement. Composites with 15% loading exhibit maximum tensile strength, followed by 10%, 5%, 20%, 25% and 30% loadings. The failure of reinforced composites under tensile load could be due to breaking of cellulosic fibers at the weaker point followed by further propagation under the applied load that is transferred to adjacent fibers by the matrix, leading to complete rupture of the composites. From the value of Young’s modulus and tensile strength reported in Table 3, it is clearly asserted that there is a gradual decrease in the strength when increasing the percentage of the hemp fibers up to 20%. The tensile strength observed is better at 15% hemp fiber. The flexural strength results of hemp fiber composites follow the same trends obtained in tensile strength tests. Table 4 shows that the flexural properties increase up to 15% of fiber, and then keep this increase, after 20% of fiber we observed also the deterioration of the mechanical properties.