Structure, property and processing relationships of all-cellulose composites

Cellulose is the main load-bearing component in plant fibre due to its covalent β-1→4- link that bonds glucose molecules into a flat ribbon and tight network of intra- and intermolecular hydrogen bonds. It is possible to manipulate the intra- and intermolecular hydrogen bonds in order to embed highly crystalline cellulose in a matrix of non-crystalline cellulose, thereby creating self-reinforced cellulose composites. Cellulose is an excellent choice of raw material for the production of sustainable and high-strength composites by selfconsolidation of cellulose since it is readily biodegradable and widely available. Nowadays, the cellulose industry makes extensive use of solvents. A multitude of solvents for cellulose is available but only a few have been explored up to the semi-industrial scale and can qualify as "sustainable" processes. An effective solvent for cellulose is a mixture of the LiCl salt and organic solvent N,N-Dimethylacetamide (DMAc). Once cellulose has been dissolved, the cellulose/LiCl/DMAc mixture can be precipitated in water. Preliminary results showed that a solution of 1 wt.% kraft cellulose in 8 wt.% LiCl/DMAc that was precipitated in water formed an hydrogel where cellulose chains were held in their amorphous state and in which no crystalline phase was detected by wide angle X-ray diffraction (WAXD). The initially amorphous cellulose started crystallizing by cross-linking of hydrogen bonds between the hydroxyl groups of the cellulose chains when the cellulose gel was dried and the water to cellulose ratio reached 7 g/g. The final form was poorly crystalline but distinct from amorphous cellulose. In order to study all-cellulose composites at a fundamental level, model all-cellulose composite films were prepared by partly dissolving microcrystalline cellulose (MCC) powder in an 8% LiCl/DMAc solution. Cellulose solutions were precipitated and the resulting gels were dried by vacuum-bagging to produce films approximately 0.2-0.3 mm thick. Wide-angle X-ray scattering (WAXS) and solid-state ¹³C NMR spectra were used to characterize molecular packing. The MCC was transformed to relatively slender crystallites of cellulose I in a matrix of paracrystalline and amorphous cellulose. Paracrystalline cellulose was distinguished from amorphous cellulose by a displaced and relatively narrow WAXS peak, by a 4 ppm displacement of the C-4 ¹³C NMR peak, and by values of T₂(H) closer to those for crystalline cellulose than disordered cellulose. Cellulose II was not formed in any of the composites studied. The ratio of cellulose to solvent was varied, with greatest transformation observed for c < 15%, where c is the weight of cellulose expressed as percentage of the total weight of cellulose, LiCl and DMAc. The dissolution time was varied between 1 and 48 h, with only slight changes occuring beyond 4 h. Transmission electron microscopy (TEM) was employed to assess the morphology of the composites. During dissolution, MCC in the form of fibrous fragments were split into thinner cellulose fibrils. The composites were tested in tension and fracture surfaces were inspected by scanning electron microscopy (SEM). It was found that the mechanical properties and final morphology of all-cellulose composites is primarily controlled by the rate of precipitation, initial cellulose concentration and dissolution time. All-cellulose composites were produced with a tensile strength of up to 106 MPa, modulus up to 7.6 GPa and strain-to-failure around 6%. The precipitation conditions were found to play a large role in the optimisation of the mechanical properties by limiting the amount of defects induced by differential shrinkage. Dynamic mechanical analysis was used to study the viscoelasticity of all-cellulose composites over temperatures ranging from -150℃ to 370℃. A β relaxation was found between -72 and -45℃ and was characterized by an activation energy of ~77.5±9.9 kJ/mol, which is consistent with the relaxation of the main chain through co-operative inter- and intramolecular motion. The damping at the β peak generally decreases with an increase in the crystallinity due to enhanced restriction of the molecular motion. For c≤15%, the crystallinity index and damping generally decreased with an increasing dissolution time, whereas the size distribution of the mobile entities increases. A simple model of crystallinity-controlled relaxation does not explain this phenomenon. It is proposed that the enhanced swelling of the cellulose in solution after higher dissolution times provides a more uniform distribution of the crystallites within the matrix resulting in enhanced molecular constriction of the matrix material. For c = 20%, however, the trend was the opposite when the dissolution time was increased. In this case, a slight increase in crystallinity and an increasing damping were observed along with a decrease in the size distribution of the mobile entities. This phenomenon corresponds to a re-crystallisation accompanied with a poor consolidation of the composite. A relaxation ɑ₂ at ~200℃ is attributed to the micro-Brownian motion of cellulose chains and is believed to be the most important glass transition for cellulose. The temperature of ɑ₂ decreased with an increase in crystallinity supposedly due to enhanced restriction of the mobile molecular phase. A high temperature relaxation which exhibited two distinct peaks, ɑ₁﹐₂ at ~300℃ and ɑ₁﹐₁ at ~320℃, were observed. ɑ₁﹐₂ is prevalent in the cellulose with a low crystallinity. A DMA scan performed at a slow heating rate enabled the determination of the activation energy for this peak as being negative. Consequently, ɑ₁﹐₂ was attributed to the thermal degradation onset of the surface exposed cellulose chains. ɑ₁﹐₁ was prevalent in higher crystallinity cellulose and accordingly corresponds to the relaxation of the crystalline chains once the amorphous portion starts degrading, probably due to slippage between crystallites. The relative ɑ₁﹐₁/ɑ₁﹐₂ peak intensity ratio was highly correlated to the amount of exposed chains on the surface of the cellulose crystallites. Novel aerogels (or aerocellulose) based on all-cellulose composites were also prepared by partially dissolving microcrystalline cellulose (MCC) in an 8 wt.% LiCl/DMAc solution. Cellulose gels were precipitated and then processed by freeze-drying to maintain the openness of the structure. The density of aerocellulose increased with the initial cellulose concentration and ranged from 116 to 350 kg.m⁻³. Aerocellulose with relatively high mechanical properties were successfully produced. The flexural strength and modulus of the aerocellulose was measured up to 8.1 MPa and 280 MPa, respectively

Structure, property and processing relationships of all-cellulose composites

Cellulose is the main load-bearing component in plant fibre due to its covalent β-1→4- link that bonds glucose molecules into a flat ribbon and tight network of intra- and intermolecular hydrogen bonds. It is possible to manipulate the intra- and intermolecular hydrogen bonds in order to embed highly crystalline cellulose in a matrix of non-crystalline cellulose, thereby creating self-reinforced cellulose composites. Cellulose is an excellent choice of raw material for the production of sustainable and high-strength composites by selfconsolidation of cellulose since it is readily biodegradable and widely available. Nowadays, the cellulose industry makes extensive use of solvents. A multitude of solvents for cellulose is available but only a few have been explored up to the semi-industrial scale and can qualify as "sustainable" processes. An effective solvent for cellulose is a mixture of the LiCl salt and organic solvent N,N-Dimethylacetamide (DMAc). Once cellulose has been dissolved, the cellulose/LiCl/DMAc mixture can be precipitated in water. Preliminary results showed that a solution of 1 wt.% kraft cellulose in 8 wt.% LiCl/DMAc that was precipitated in water formed an hydrogel where cellulose chains were held in their amorphous state and in which no crystalline phase was detected by wide angle X-ray diffraction (WAXD). The initially amorphous cellulose started crystallizing by cross-linking of hydrogen bonds between the hydroxyl groups of the cellulose chains when the cellulose gel was dried and the water to cellulose ratio reached 7 g/g. The final form was poorly crystalline but distinct from amorphous cellulose. In order to study all-cellulose composites at a fundamental level, model all-cellulose composite films were prepared by partly dissolving microcrystalline cellulose (MCC) powder in an 8% LiCl/DMAc solution. Cellulose solutions were precipitated and the resulting gels were dried by vacuum-bagging to produce films approximately 0.2-0.3 mm thick. Wide-angle X-ray scattering (WAXS) and solid-state ¹³C NMR spectra were used to characterize molecular packing. The MCC was transformed to relatively slender crystallites of cellulose I in a matrix of paracrystalline and amorphous cellulose. Paracrystalline cellulose was distinguished from amorphous cellulose by a displaced and relatively narrow WAXS peak, by a 4 ppm displacement of the C-4 ¹³C NMR peak, and by values of T₂(H) closer to those for crystalline cellulose than disordered cellulose. Cellulose II was not formed in any of the composites studied. The ratio of cellulose to solvent was varied, with greatest transformation observed for c < 15%, where c is the weight of cellulose expressed as percentage of the total weight of cellulose, LiCl and DMAc. The dissolution time was varied between 1 and 48 h, with only slight changes occuring beyond 4 h. Transmission electron microscopy (TEM) was employed to assess the morphology of the composites. During dissolution, MCC in the form of fibrous fragments were split into thinner cellulose fibrils. The composites were tested in tension and fracture surfaces were inspected by scanning electron microscopy (SEM). It was found that the mechanical properties and final morphology of all-cellulose composites is primarily controlled by the rate of precipitation, initial cellulose concentration and dissolution time. All-cellulose composites were produced with a tensile strength of up to 106 MPa, modulus up to 7.6 GPa and strain-to-failure around 6%. The precipitation conditions were found to play a large role in the optimisation of the mechanical properties by limiting the amount of defects induced by differential shrinkage. Dynamic mechanical analysis was used to study the viscoelasticity of all-cellulose composites over temperatures ranging from -150℃ to 370℃. A β relaxation was found between -72 and -45℃ and was characterized by an activation energy of ~77.5±9.9 kJ/mol, which is consistent with the relaxation of the main chain through co-operative inter- and intramolecular motion. The damping at the β peak generally decreases with an increase in the crystallinity due to enhanced restriction of the molecular motion. For c≤15%, the crystallinity index and damping generally decreased with an increasing dissolution time, whereas the size distribution of the mobile entities increases. A simple model of crystallinity-controlled relaxation does not explain this phenomenon. It is proposed that the enhanced swelling of the cellulose in solution after higher dissolution times provides a more uniform distribution of the crystallites within the matrix resulting in enhanced molecular constriction of the matrix material. For c = 20%, however, the trend was the opposite when the dissolution time was increased. In this case, a slight increase in crystallinity and an increasing damping were observed along with a decrease in the size distribution of the mobile entities. This phenomenon corresponds to a re-crystallisation accompanied with a poor consolidation of the composite. A relaxation ɑ₂ at ~200℃ is attributed to the micro-Brownian motion of cellulose chains and is believed to be the most important glass transition for cellulose. The temperature of ɑ₂ decreased with an increase in crystallinity supposedly due to enhanced restriction of the mobile molecular phase. A high temperature relaxation which exhibited two distinct peaks, ɑ₁﹐₂ at ~300℃ and ɑ₁﹐₁ at ~320℃, were observed. ɑ₁﹐₂ is prevalent in the cellulose with a low crystallinity. A DMA scan performed at a slow heating rate enabled the determination of the activation energy for this peak as being negative. Consequently, ɑ₁﹐₂ was attributed to the thermal degradation onset of the surface exposed cellulose chains. ɑ₁﹐₁ was prevalent in higher crystallinity cellulose and accordingly corresponds to the relaxation of the crystalline chains once the amorphous portion starts degrading, probably due to slippage between crystallites. The relative ɑ₁﹐₁/ɑ₁﹐₂ peak intensity ratio was highly correlated to the amount of exposed chains on the surface of the cellulose crystallites. Novel aerogels (or aerocellulose) based on all-cellulose composites were also prepared by partially dissolving microcrystalline cellulose (MCC) in an 8 wt.% LiCl/DMAc solution. Cellulose gels were precipitated and then processed by freeze-drying to maintain the openness of the structure. The density of aerocellulose increased with the initial cellulose concentration and ranged from 116 to 350 kg.m⁻³. Aerocellulose with relatively high mechanical properties were successfully produced. The flexural strength and modulus of the aerocellulose was measured up to 8.1 MPa and 280 MPa, respectively

Calibration and validation of the STICS crop model for managing wheat irrigation in the semi-arid Marrakech/Al Haouz Plain

In the first part of this work, the shoot growth module and grain yield of the STICS crop model were calibrated and validated by using field data which was collected from irrigated winter wheat fields in the Haouz plain near Marrakech. The calibration was performed on the thermal units between the four phenological stages that control the dynamics of leaf area index and the thermal unit between emergence and the beginning of grain filling. The plant phenology was calibrated for three fields monitored during the 2002/03 season. Evaluation of the grain yields and the temporal evolution of leaf area index were done for six validation fields during 2003/04. The results showed the significant accuracy of the model in simulating these variables, and also indicated that the plants mainly suffered from lack of nitrogen. The results in the second part show the potential of crop modeling to schedule irrigation water, on the assumption that the plants were growing under optimal conditions of fertilization. In this case, the model was used to manage the time of irrigation according to a threshold for water deficit. Various simulations displayed logical trends in the relationship between the grain yield and both the amount and timing of irrigation water. These results were finally compared with those obtained from real irrigation practices. For the particular climate of 2003/04, the comparison showed that 70 mm and 40 mm of water could be saved in case of early and late sowing, respectively

Derived crop coefficients for winter wheat using different reference evpotranspiration estimates methods

This paper reports the results of using three empirical methods (Makkink, Priestley-Taylor and Hargreaves) for estimating the reference evapotranspiration (ET0) in the semi-arid region of Tensift Al Haouz, Marrakech (center of Morocco). The Penman-Monteith equation, standardized by the Food and Agriculture Organization (FAO-PM), is used to evaluate the three empirical methods. The obtained ET0 data were used to estimate crop water requirement (ET) of winter wheat using the crop coefficient (K-c) approach and results were compared with ET measured by the Eddy Covariance technique. The result showed that using the original empirical coefficients a, alpha and C-m in Hargreaves, Priestley-Taylor and Makkink equations, respectively, the Hargreaves method agreed fairly well with FAO-PM method at the test site. Conversely, the Priestley-Taylor and Makkink methods underestimate the ET by about 20 and 18 %. After adjustment of the original values of two parameters alpha and C-m coefficients in Priestley-Taylor and Makkink equations, the underestimation of ET was reduced to 9% and 4% for the Priestley Taylor and Makkink methods, respectively, which led to an improvement of 55% and 76% of the obtained values compared with the original values

Estimation of the dynamics and yields of cereals in a semi-arid area using remote sensing and the SAFY growth model

International audienceIn semi-arid areas, a strongly variable climate represents a major risk for food safety. An operational grain yield forecasting system, which could help decision-makers to make early assessments and plan annual imports, is thus needed. It can be challenging to monitor the crop canopy and production capacity of plants, especially cereals. In this context, the aim of the present study is to analyse the characteristics of two types of irrigated and non-irrigated cereals: barley and wheat. Through the use of a rich database, acquired over a period of two years for more than 30 test fields, and from 20 optical satellite SPOT/HRV images, two research approaches are considered. First, statistical analysis is used to characterize the vegetation's dynamics and grain yield, based on remotely sensed (satellite) normalized difference vegetation index (NDVI) measurements. A relationship is established between the NDVI and LAI (leaf area index). Different robust relationships (exponential or linear) are established between the satellite NDVI index acquired from SPOT/HRV images, just before the time of maximum growth (April), and grain and straw, for barley and wheat vegetation covers. Following validation of the proposed empirical approaches, yield maps are produced for the studied site. The second approach is based on the application of a Simple Algorithm for Yield Estimation (SAFY) growth model, developed to simulate the dynamics of the LAI and the grain yield. An inter-comparison between ground yield measurements and SAFY model simulations reveals that yields are underestimated by this model. Finally, the combination of multi-temporal satellite measurements with the SAFY model estimations is also proposed for the purposes of yield mapping. Although the results produced by the SAFY model are found to be reasonably well correlated with those determined by satellite measurements (NDVI), the grain yields are nevertheless underestimated

Water use efficiency and yield of winter wheat under different irrigation regimes in a semi-arid region

In irrigation schemes under rotational water supply in semi-arid region, the water allocation and irrigation scheduling are often based on a fixed-area proportionate water depth with every irrigation cycle irrespective of crops and their growth stages, for an equitable water supply. An experiment was conducted during the 2004- 2005 season in Haouz irrigated area in Morocco, which objective was 1) to evaluate the effects of the surface irrigation scheduling method (ex-isting rule) adopted by the irrigation agency on winter wheat production compared to a full ir-rigation method and 2) to evaluate drip irrigation versus surface irrigation impacts on water sav-ing and yield of winter wheat. The methodology was based on the FAO-56 dual approach for the surface irrigation scheduling. Ground measure- ments of the Normalized Difference Vegetation Index (NDVI) were used to derive the basal crop coefficient and the vegetation fraction cover. The simple FAO-56 approach was used for drip irrigation scheduling. For surface irrigation, the existing rule approach resulted in yield and WUE reductions of 22% and 15%, respectively, compared with the optimized irrigation sched-uling proposed by the FAO-56 for full irrigation treatment. This revealed the negative effects of the irrigation schedules adopted in irrigation schemes under rotational water supply on crops productivity. It was also demonstrated that drip irrigation applied to wheat was more efficient with 20% of water saving in comparison with surface irrigation (full irrigation treatment). Drip irrigation gives also higher wheat yield com-pared to surface irrigation (+28% and +52% for full irrigation and existing rule treatments re-spectively). The same improvement was ob-served for water use efficiency (+24% and +59% respectively)

From Cellulose Dissolution and Regeneration to Added Value Applications — Synergism Between Molecular Understanding and Material Development

Modern society is now demanding “greener” materials due to depleting fossil fuels and increasing environmental awareness. In the near future, industries will need to become more resource-conscious by making greater use of available renewable and sustainable raw materials. In this context, agro-forestry and related industries can indeed contribute to solve many resource challenges for society and suppliers in the near future. Thus, cellulose can be predicted to become an important resource for materials due to its abundance and versatility as a biopolymer. Cellulose is found in many different forms and applications. However, the dissolution and regeneration of cellulose are key (and challenging) aspects in many potential applications. This chapter is divided into two parts: (i) achievements in the field of dissolution and regeneration of cellulose including solvents and underlying mechanisms of dissolution; and (ii) state-of-the-art production of value-added materials and their applications including manmade textile fibers, hydrogels, aerogels, and all-cellulose composites, where the latter is given special attention

Soil texture estimation over a semiarid area using TerraSAR-X radar data

In this letter, it is proposed to use TerraSAR-X data for analysis and estimation of soil surface texture. Our study is based on experimental campaigns carried out over a semiarid area in North Africa. Simultaneously with TerraSAR-X radar acquisitions, ground measurements (texture, soil moisture, and roughness) were made on different test fields. A strong correlation is observed between soil texture and a processed signal from two radar images, with the first acquired just after a rain event and the second corresponding to dry soil conditions, acquired three weeks later. An empirical relationship is proposed for the retrieval from radar signals of clay content percent. Soil texture mapping is proposed over the study site, which includes bare soils and olive groves

Agrometerological study of semi-arid areas : an experiment for analysing the potential of time series of FORMOSAT-2 images (Tensift-Marrakech plain)

Earth Observing Systems designed to provide both high spatial resolution (10m) and high capacity of time revisit (a few days) offer strong opportunities for the management of agricultural water resources. The FORMOSAT-2 satellite is the first and only satellite with the ability to provide daily high-resolution images over a particular area with constant viewing angles. As part of the SudMed project, one of the first time series of FORMOSAT-2 images has been acquired over the semi-arid Tensift-Marrakech plain. Along with these acquisitions, an experimental data set has been collected to monitor land-cover/land-use, soil characteristics, vegetation dynamics and surface fluxes. This paper presents a first analysis of the potential of these data for agrometerological study of semi-arid areas

The sustainability of phytomass-derived materials: thermodynamical aspects, life cycle analysis and research perspectives

International audienceCellulose in particular and phytomass in general are at the heart of our food system. They are also a central energy vector and a vital source of materials. In this article, a multiscale approach to the complex issue of lignocellulose sustainability is developed. Global thermodynamic concepts help to place current biomass exploitation in a global energetic context. In particular, the notion of entropy appears pivotal to understand energy and material fluxes at the scale of the planet and the limits of biomass production. Entropy is, however, best described at the microscopic scale, despite its large-scale consequences. Recent advances in entropy-driven colloid assembly parallel nature's choices and lignocellulose assembly at the nanometric scale. The functional concept of exergy is then developed and a few examples of its concrete use in photosynthesis and biorefinery research are given. In a subsequent part, an evaluation of the relative importance of biomass is performed with respect to non-renewable materials. This discussion helps to explain the interdependence of resources, including ores and fossil fuels. This interdependence has important consequences for current and future biomass uses. Some of these dependences are then quantitatively discussed using life cycle analysis (LCA) results from the literature. These results are of importance to different technological fields such as paper, biobased insulation, construction wood, information and communication technologies, and biobased textiles. A conclusion is then drawn that exposes the research tracks that are the most likely to be sustainable, including self-assembly, exergetically favourable options and low tech solutions