Hemp Bast Fibers Research Articles

Carbohydrate components and crystalline structure of organosolv hemp ( Cannabis sativa L.) bast fibers pulp

Changes in carbohydrate components and crystalline structure of hemp bast fibers during organosolv pulping were investigated by X-ray diffractometry, FT-IR spectroscopy and high performance liquid chromatography (HPLC). The reasons for defibrillation and beating problems with organosolv hemp bast fiber pulp were investigated with reference to these properties of pulp samples. Hemp bast fibers and organosolv pulp samples had low hemicellulose contents and high cellulose contents. It was found that the disorder parameter of cellulose in hemp bast fibers was very low, when crystalline cellulose ratio was high and the crystalline structure of cellulose in hemp bast fibers was very stable. These properties affected defibrillation and beating of organosolv hemp bast fibers pulp negatively.

Dependence of chemical and crystalline structure of alkali sulfite pulp on cooking temperature and time

This study investigates the change in chemical and crystalline structure of pulp samples during alkali sulfite process at different cooking temperatures and time, TAPPI and SCAN standard test methods and X-ray diffraction and FT-IR spectroscopy were used. It was shown that the crystalline structure of cellulose in hemp ( Cannabis sativa L.) bast fibers was very strong and stable. Crystallinity of alkali sulfite pulp samples obtained from processing at 140 up to 180 °C increased, but then decreased at 200 °C. The crystallite size of cellulose in alkali sulfite pulp samples increased with cooking temperature. The crystalline allomorph of cellulose in alkali sulfite pulp samples obtained at 200 °C changed from monoclinic structure to triclinic structure. Crystalline structure of cellulose in alkali sulfite pulp samples was little affected by changing cooking time. It was concluded that cooking temperature during alkaline sulfite pulping process had more effect on carbohydrate components and crystalline structure of pulp samples than cooking time.

Chemical Characterization of Lignin and Lipid Fractions in Industrial Hemp Bast Fibers Used for Manufacturing High-Quality Paper Pulps

The chemical composition of lignin and lipids of bast fibers from industrial hemp (Cannabis sativa) used for high-quality paper pulp production was studied. Pyrolysis-gas chromatography/mass spectrometry (Py-GC/MS) of fibers showed a lignin with a p-hydroxyphenyl:guaiacyl:syringyl unit (H:G:S) molar proportion of 13:53:34 (S/G ratio of 0.64). p-Hydroxycinnamic acids, namely, p-coumaric and ferulic acids, were found in only trace amounts. Among the lipids, the main compounds identified by GC/MS of the hemp fibers extracts were series of n-alkanes, free and esterified sterols and triterpenols, waxes, and long-chain n-fatty acids. Other compounds such as n-aldehydes, n-fatty alcohols, steroid hydrocarbons, and steroid and triterpenoid ketones as well as steryl glycosides were also found.

Structure and Chemical Composition of Bast Fibers Isolated from Developing Hemp Stem

Microscopic and chemical changes of hemp bast fibers were studied during the maturation from vegetative to grain maturity stages at both apical and basal regions of the stems. The content of protein was the main factor related to fiber maturation, whereas increased proportions of mannose and glucose and decreasing levels of galactose were also highly significant. Enhanced glucose deposition in apical fibers could be related to the gradual thickening of the fibers, whereas in basal regions the thickness of the fibers nearly reached the maximum at vegetative stages. In contrast, the extent of lignification remained close to 3-4% during plant growth. Hemp fiber lignins were rich in guaiacyl units and would be rather condensed in nature. In addition, the proportion of p-hydroxyphenyl units displayed a constant decline during maturation. A progressive chemical fractionation of hemp fibers provided further insights to the occurrence and nature of noncellulosic polysaccharides. Notably, these data pointed out that maturation is accompanied by a significant increase in water- and alkali-soluble components containing glucose- and mannose-related polymers and a decrease in arabinose and galactose components disrupted by diluted hydrochloric acid. Taken together, chemical features of the noncellulosic components suggest that the architecture of hemp fibers differs slightly from that of the more widely studied flax fibers.

Properties of ball milled thermally treated hemp fibers in an inert atmosphere for potential composite reinforcement

Hemp (emph{Cannabis Sativ L}.) is an important lignocellulosic raw material for the manufacture of cost-effective environmentally friendly composite materials. From an earlier experiment it was found that when hemp bast fibers were heated between 160∘C and 260∘C, there was softening of lignin leading to opening of fibers and the preliminary observations showed that heat treatment at 220∘C in an inert environment seemed to provide enough fiber without affecting the associated tissues of the fibers. However, these heat treated fibers need to be separated by mechanical action. For this experiment, hemp fibers were given heat treatment in an enclosed vessel in a nitrogen environment at 220∘C for 30 min and then they were ball milled. It was found that there was further opening of fibers upon ball milling of the heated fibers and the total number of fibers increased for the equal weight of fibers. It was not possible to find strength properties of shorter length fibers; however, the results from shorter clamping length indirectly indicated that these fibers were of higher strength. The ball milled fibers also contained copious amount of fines which must be removed before using the fibers for composite manufacturing.

The effect of alkalization and fibre alignment on the mechanical and thermal properties of kenaf and hemp bast fibre composites: part 2 – cashew nut shell liquid matrix

Long and random hemp and kenaf fibres were used in as-received condition and alkalized in a 6% NaOH solution. They were combined with cashew nut shell liquid (CNSL) resin and hot-pressed to form natural fibre, natural matrix composites. The mechanical properties of the composites were investigated to observe the effect of fibre alignment and alkalization. A general trend was observed whereby alkalized and long fibre composites gave higher flexural modulus and flexural strength with alkalized long kenaf–CNSL composite giving superior mechanical properties. A general trend was also observed for the overall mechanical test results of the composites whereby high flexural modulus and high flexural strength are associated with a low work of fracture. Wide endothermic peaks present in differential thermal analysis thermograms for all of the composites indicated the presence of moisture which leads to inferior mechanical properties. Dynamic mechanical thermal analysis carried out on the composites showed that the alkalized fibre composites have higher E ′ and lower tan δ, corresponding to the trends of higher flexural modulus and lower work of fracture respectively.

The effect of alkalization and fibre alignment on the mechanical and thermal properties of kenaf and hemp bast fibre composites: Part 1 – polyester resin matrix

Long and random hemp and kenaf fibres were used in the as-received condition and alkalized with a 0.06 M NaOH solution. They were combined with polyester resin and hot-pressed to form natural fibre composites. The mechanical properties of the composites were measured to observe the effect of fibre alignment and alkalization. A general trend was observed whereby alkalized and long fibre composites gave higher flexural modulus and flexural strength compared with composites made from as-received fibres. Alkalized long kenaf–polyester composites possessed superior mechanical properties to alkalized long hemp–polyester composites. For the hemp–polyester composites a high flexural modulus and a high flexural strength are associated with a low work of fracture. Scanning electron microscopy micrographs of the treated hemp and kenaf fibres showed the absence of surface impurities which were present on the untreated fibres. Apparent density measurements on hemp and kenaf fibres did not show a significant change after alkalization with 0.06 M NaOH. Wide endothermic peaks present in differential thermal analysis thermograms for all of the composites indicated the presence of moisture which leads to inferior mechanical properties. Dynamic mechanical thermal analysis carried out on the polyester matrix composites showed that the alkalized fibre composites have higher E ′ values corresponding to higher flexural moduli. Any correlation between fibre surface treatment and the work of fracture and tan δ of composites is less clear.

Mechanical properties of thermally treated hemp fibers in inert atmosphere for potential composite reinforcement

Hemp (Cannabis Sativ L.) is an important lignocellulosic raw material for the manufacture of cost-effective environmentally friendly composite materials. From an earlier study it was found that when hemp bast fibers were heated above the glass transition temperature of lignin, there was a migration of lignin to the surface of the fiber. The preliminary observations showed that heat treatment in inert environment seemed to provide enough fiber opening without affecting the associated tissues of the fibers. Here, hemp fibers were given heat treatment in an enclosed vessel in air as well as inert environment and their mechanical properties were compared to the raw hemp fiber. It was found that there were openings of fibers upon heating, both along the length as well as along the diameter or the width directions. For the same weight of the fiber, the total count of fibers increased during heat treatment, with increment up to 32% for inert environment and 39% for air environment; the increment was mainly due to opening up of fibers into lesser diameters than the original fibers. The strength properties were strongly influenced by the diameter of the fibers, with the lesser fibers contributing to greater tensile strength and modulus. The overall tensile strength and modulus of fibers treated in inert environment were found to have increased, probably due to production of fibers of lesser diameters, presumably with less number of natural defects. The overall strength of fiber treated in air environment, however, decreased even though there was opening up of fibers in this case as well. This was due to oxidation of various constituents of fiber which contributes strength.

Hemp(Cannabis sativaL.) Cultivation in North-Central Turkey

Abstract This paper summarizes the history of hemp (Cannabis sativa L.) cultivation and traditional use in the north-central region of Turkey, and investigates the cultivation and processing techniques currently being used to produce hemp bast fiber and hemp seed. Hemp bast fibers are used by the Turks for making paper, hand-made rope, and machine processed twine and rope. The hurd is used locally for kindling. The flowers are used for compost and the seeds are used for human food and bird feed. The use of hemp in recent years has declined significantly. The cultural and economic reasons for the reduced cultivation and use of hemp are discussed.

Application of an alkaline and thermostable polygalacturonase from Bacillus sp. MG-cp-2 in degumming of ramie ( Boehmeria nivea) and sunn hemp ( Crotalaria juncea) bast fibres

An alkaline (optimum pH 10.0) and thermo stable (optimum temperature 60°C) polygalacturonase from Bacillus sp. MG-cp-2 has been applied for the degumming of ramie ( Boehmeria nivea) and sunn hemp ( Crotalaria juncea) bast fibres in comparison to the conventional chemical degumming process. Sunn is an East Indian plant with a valuable fibre resembling hemp and lighter and stronger than jute. Of the three treatments i.e. enzymic, chemical, and ‘chemical+enzyme’, the third treatment was most promising for degumming. The maximum reducing sugar released from the ramie and sunn hemp fibre were 9.4 and 7.6 μmol/ml, respectively, whereas the percent reduction in the fibre weight of ramie and sunn hemp fibre were 37 and 56%, respectively, after 11 h of treatment with chemical and enzyme. The scanning electron microscopic studies also revealed a complete removal of non-cellulosic gummy material from the surface of ramie and sunn hemp fibres. On the basis of this study, it is recommended that a mild chemical treatment of plant fibre is necessary before its enzymic treatment, since neither chemical nor enzymic treatment is sufficient.

Compressibility of hemp bast fibres

A force-based characterization of the extrusion pulping process is necessary to be able to predict the effects of extrusion on fibres. To determine which forces are beneficial and which only cause energy consumption, the nature and the origin of the forces have to be known. This paper discusses the behaviour of hemp bast fibres under compression to better understand the underlying mechanisms involved in the application of energy to the fibres. Untreated, water soaked and NaOH-soaked hemp bast fibres were subjected to varying loads and loading rates and the resulting stress-density and relaxation curves were studied. The stress-density relationship of hemp bast fibres was described with the compressibility equation. The coefficient of the compressibility equation decreased with temperature and moisture content. Fibres became more flexible and fibre bending became more important in the mechanism of fibre compression. The higher flexibility resulted in a lower stress over the whole density range. The compressibility equation also applied to the stress-density curve during compression of soaked fibres at low densities. However, at higher density the stress increased faster, because of flow resistance caused by the dense fibre mat. The flow limitation was advanced at higher strain rates and enhanced at higher sodium hydroxide concentrations. Relaxation was described with a generalized Maxwell model. The extent of relaxation slightly decreased with increasing maximum stress, increased with strain rate and increased with moisture content. Soaked fibres showed a much higher relaxation, which, however, was mostly caused by the high maximum stress because of the flow resistance at higher densities. When regarding the solid stress instead of the total stress, relaxation appeared to be lower. Mechanical pulping processes should therefore be operated at such low strain rates, that the stress observed only depends on the density obtained and not on the flow resistance. During repeated compression both maximum stress and the extent of relaxation decreased with the number of repetitions and the total plastic strain increased until a point was reached at which no further changes were observed. However, the total plastic strain showed a higher dependence on the maximum stress during repeated compression than on the number of compressions. Repeat compression of wet fibres resulted in the formation of a compact fibre mat with a high flow resistance causing high stress peaks.

Structural features of the pectic polysaccharides isolated from retted hemp bast fibres

Pectic polysaccharides were solubilized from retted hemp bast fibre bundles, by sequential extraction with water and ammonium oxalate at 100 °C. The polysaccharides isolated from the extracts were de-esterified and fractionated by anion exchange chromatography, yielding five fractions from boiling water extract and five fractions from oxalate extract. Five of these fractions were characterized by chemicals methods, 1H and 13C NMR, as polysaccharides containing galacturonic acid, rhamnose and galactose units in variable ratios. Their chemical structure comprises a disaccharide repeating unit → 2)- α-l-Rha p-(1 → 4)- α-Gal pA-(1 → backbone, with short side chains attached to the rhamnosyl residues. The β- d-Galactose residues are attached to O-4 of the rhamnosyl residues, but the amount of l-rhamnosyl residues that are 2,4-linked can vary from 36 to 75%, from one fraction to another. A fraction corresponding to a mixture of oligosaccharides with an average dp of 13, with ten galacturonic acid, two rhamnose and one galactose units was also isolated.

Morphological characterization of steam-exploded hemp fibers and their utilization in polypropylene-based composites

An investigation is described in which the morphology of hemp stem was examined by optical and scanning electron microscopy. We reported the results concerning steam-explosion treatment either on bast fibers impregnated with alkaline liquor or on woody hemp chènevotte samples impregnated under neutral, acidic and alkaline conditions. The influence of steam-explosion treatment parameters were followed by optic and scanning electron microscopy, chemical composition and evolution of the average (DP v) values of the purified samples. Hemp bast fibers purified by steam treatment were compounded with polypropylene (PP), either directly or after surface treatment with polypropylene-maleic anhydride co-polymer (PPMA). Polypropylene/hemp fibers composite films with various amount of fibers were prepared and their mechanical properties were improved, in particular when fibers treated with PPMA were used.