Modified Hemp Fibers Research Articles

Impact of Surface Modification of Hemp Fibers Using a Coupling Agent in Solvent on the Properties of Polyethylene Composites

This study investigates the grafting of a coupling agent, maleic anhydride-grafted polyethylene (MAPE), onto hemp fibers in a 1,2,4-trichlorobenzene (TCB) solution, followed by an evaluation of the morphological, rheological, and mechanical properties of the resulting polyethylene composites containing 30% hemp. The SEM analysis revealed that a thin layer of MAPE formed on the surface of the modified fibers. This was further confirmed by the appearance of a MAPE degradation peak at 448°C, observed in the modified fibers but absent in the unmodified counterparts. Composites made with unmodified hemp fibers (UT30) showed a significant increase in modulus but not in tensile strength. In contrast, the modification of hemp in solution significantly enhanced the tensile strength of the composites (UTE3S) without significantly affecting the modulus. Increasing the amount of coupling agent (in UTE6S and UTE9S) reinforced this trend, indicating that the thin polymer layer on the surface of the modified hemp fibers notably improved interfacial bonding, with minimal impact on the tensile modulus of the composites.

Application of Natural (Plant) Fibers Particularly Hemp Fiber as Reinforcement in Hybrid Polymer Composites - Part III. Investigations of Physical and Mechanical Properties of Composites Reinforced with Hemp Fibers

ABSTRACT The article is the third part of a multi-directional analysis of the possibilities, advisability and validity of using natural plant fibers (NPFs) as a reinforcement for polymer structural composites that can be used in the shipbuilding industry in Poland. As a result of the analysis of macroeconomic indicators and natural and non-natural factors regarding NPFs, a representative selection of hemp (Cannabis sativa L.) was made as the raw material to be used to reinforce these composites. Methods and test results are presented enabling comparison of the physical and mechanical properties of the new pro-ecological construction material–hemp fiber reinforced polymer (HFRP), reinforced with fabric made of unmodified and chemically modified hemp fibers.

Modified hemp fibers as a novel and green adsorbent for organic dye adsorption: adsorption, kinetic studies and modeling

Synthetic dyes represent a serious hazard to aquatic environments. Many approaches for eliminating these contaminants have been devised and applied. This manuscript reports the production of a novel, low-cost and ecologically friendly bioadsorbent based on hemp fibers that are functionalized with graphite oxide through bridging with an organosilane. Methylene blue was selected as a typical pollutant to be removed from wastewaters. The adsorbent was characterized through scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDX) and Fourier-transform infrared (FTIR) analysis. An investigation of the effects of pH and temperature on the adsorption process was carried out. The adsorption capacity increased with increasing contact time as well as with the temperature, proving that the process shows endothermic behavior. Moreover, the process was found to be dependent on the pH level and, to corroborate the collected results, the point of zero charge was evaluated. The maximum adsorption capacity was found to be 57 mg/g, which was achieved with the following parameters: pH = 7.5, T = 80 °C and an initial dye concentration equal to 5 mg/L. Reusability studies showed a 15% decrease in adsorption capacity after 30 adsorption tests, proving the possibility of reusing the produced adsorbent without any great decay in performance. Finally, a potential adsorption mechanism is reported and discussed. The reported results prove that it is feasible to apply the designed adsorbent of organic dyes to the purification of wastewaters.Graphical abstract

CHEMICAL MODIFICATION FOR RESISTANCE TO PHOTO-OXIDATIVE DEGRADATION AND IMPROVED BLEACHING AND COLOR FASTNESS PROPERTIES OF HEMP FIBER

The objective of the research has been to overcome some inherent drawbacks of hemp fiber via chemical modification, which is a vital issue in using it as a textile fiber like cotton. Hemp fiber was modified with treatment liquor (mixture of sulfurous acid and sodium hydroxide) in aqueous medium to remove lignin. The effects of the treatment liquor concentration, fiber to liquor ratio, reaction time and temperature on the percent lignin extracted from hemp fiber were studied. Modified hemp fibers (MHF) were bleached in an alkaline pH aqueous medium with hydrogen peroxide. The process significantly improved lignin removal, bleaching and color fastness. In fact, the whiteness index of bleached MHF was significantly higher than that of bleached raw hemp, but its tensile strength was slightly affected. The photo-oxidative degradation of hemp fiber was 70% lower than that of unmodified (raw) hemp fiber and almost like that of cotton yarn. The color fastness properties of dyed bleached modified hemp fiber were significantly better than those of dyed bleached unmodified hemp fiber and close to those of dyed bleached cotton yarn.

Fabrication of novel hybrid materials based on iron-aluminum modified hemp fibers: Comparison between two proposed methodologies

This paper reports the fabrication of novel hybrid and structured materials by using hemp fibers as organic support. Two in-situ methodologies were proposed and applied to modify the surface of hemp fibers in order to improve their physical properties and to confer a magnetic behavior: i) coprecipitation of Fe/Al layered double hydroxides through urea method (MHF@LDH Fe/Al) and ii) deposition of Fe3O4 particles onto AlOOH modified hemp fibers in ammonia solution (MHF@AlOOH-FePs). The obtained hybrid materials have been widely characterized in terms of spectroscopic, morphological, thermal and barrier properties. Finally, a further investigation concerned the evaluation of surface charge and the estimation of magnetic properties showing a ferromagnetic behavior (Curie Temperature Tc > 300 K) for both samples with a coercive field of Hc ≈± 40 Oe for MHF@LDH Fe/Al and Hc ≈ ± 10 Oe for MHF@AlOOH-FePs.

Oxidized Hemp Fibers with Simultaneously Increased Capillarity and Reduced Moisture Sorption as Suitable Textile Material for Advanced Application in Sportswear

Applications of hemp fibers, as a promising natural material in the textile field, mostly require improved fiber properties. In this paper, the oxidation of hemp fibers with potassium permanganate was applied to reduce the amount of non-cellulosic substances and moisture sorption; to introduce functional groups and increase capillarity; make fibers finer, softer and suitable for application in sport wears. The changes in sorption properties were characterized by capillary rise measurement and the ability of water retention and moisture sorption, while changes in mechanical properties were estimated by determination of tenacity and elongation of modified hemp fibers in comparison to the appropriate characteristic of unmodified fibers. ATR-FTIR, SEM techniques, and zeta potential measurement were used for the characterization of fiber structure, morphological and electrokinetic properties. We obtained a finer fiber with increased capillarity (up to 3.68 times) but reduced moisture sorption (down to 1.5 times) and water retention capacity (down to 2.8 times), with accomplished satisfactory preservation of mechanical properties. Obtained oxidized hemp fibers with attained features present a very suitable material for sportswear production. Additionally, in this paper, an improvement of the capillary rise measurement is given.

Behavior of polyethylene composites based on hemp fibers treated by surface‐initiated catalytic polymerization

AbstractIn this investigation, hemp fibers were‐surface treated by ethylene polymerization grafting to determine the effect of high grafting level on the mechanical (tensile and impact) and dynamic mechanical properties of linear medium‐density polyethylene (L) composites (20%wt.) produced via melt compounding. The results showed that, comparing the treated hemp composite (L20PH) with the untreated hemp composite (L20H), the modification reduced by 44% the modified fibers composite water absorption, while increasing the elongation and tensile strength by about 197% and 14%, respectively. Moreover, due to better interfacial interactions with the matrix and the flexibility imparted by the presence of both grafted and ungrafted polyethylene (PE) onto modified hemp fibers, the corresponding composite exhibited lower density and significantly high impact resistance (about 57%) compared to the untreated hemp composite. These results were confirmed by the composites creep strain as L20PH and L maximum strain (εmax) was respectively 18% and 42% higher compared to that of L20H, showing that L20H has the high modulus followed by L20PH and then L. The significant improvement of the modified composite flexibility, impact resistance and the limited reduction of its modulus make this material not only suitable for building and construction applications, but also in the production of packaging and automotive parts.

Modified hemp fibers intended for fiber‐reinforced polymer composites used in structural applications—A review. I. Methods of modification

AbstractNatural fiber composites have experienced a renaissance in the last two decades as a response to societal demands for developing eco‐friendly, biodegradable and recyclable materials. They are now being extensively used in everyday products as well as in automotive, packaging, sports and construction industries. Hemp fiber is being used in most of these products because of its superior mechanical properties. Like other natural fibers, hemp fibers require modifications in order to improve their properties and interfacial bonding with polymer matrices, and to reduce their hydrophilic character. These modification methods can be grouped into three major categories: chemical, physical and biological. Chemical methods use chemical reagents to reduce fibers' hydrophilic tendency and thus improve compatibility with the matrix. They also expose more reactive groups on the fiber surface to facilitate efficient coupling with the matrix. Physical methods change structural and surface properties of the fiber and thereby influence the interfacial bonding with matrices, without extensively changing the chemical composition of the fibers. They are cleaner and simpler than the chemical methods. Biological methods use biological agents like fungi, enzymes and bacteria to modify the fiber surface properties. These methods are not toxic like chemical methods and are not energy‐intensive like physical methods. This paper presents an overview of recent developments in these methods. It is concluded that these methods almost invariably result in improvement in fiber/matrix interfacial bonding, resulting in increase in mechanical properties of the composites.

Influence of fiber volume fractions on the performances of alkali modified hemp fibers reinforced cyanate ester/benzoxazine blend composites

In this current study, alkali treated eco-friendly hemp fibers were chosen to reinforce thermosetting resin blend composed of cyanate ester and benzoxazine resin. For various volume fractions ranging from 5 to 20 vol % with a regular increment of 5 vol%, their effects on the morphological, mechanical behaviour and water uptake properties were experimentally evaluated using the scanning electron microscopy, flexural, tensile and water uptake tests. The produced composites possessed much ameliorated flexural properties as compared to those of the unfilled resin. Data from the tensile test revealed a continuous increase in the composites' tensile strength and modulus as the proportion of the treated fibers augmented. Furthermore, the tensile experimental results were compared to the most commonly used empirical models like the rule of mixture (ROM), revised rule of mixture (RROM), inverse rule of mixture (IROM), Halpin Tsai (HT), Lewis and Nielson (LN), and Halpin Kardos (HK) models. It was found that the alkali treated fibers were arranged in a 3D random fiber arrangement according to the RROM model and the HK model was identified to fit well the tensile experimental results. The experimental results and theoretical modeling confirmed that the water absorption in the produced composites was increased and governed by the Fickian diffusion. These effects took place due to the chemical and morphological changes in the treated fiber external surfaces, which promoted better interfacial adhesion between the plant fibers and the polymer blend matrix.

Preparation and characterization of silver-loaded hemp fibers with antimicrobial activity

The objective of this research was to impart antimicrobial properties to hemp fibers by incorporation of silver ions in hemp fibers by chemisorption. Sorption properties of hemp fibers were improved by non-selective oxidation using hydrogen peroxide and potassium permanganate. The optimal conditions for silver ions sorption by hemp fibers were determined by changing sorption conditions: pH value and concentration of aqueous silver nitrate solution, as well as duration of sorption. The maximum sorption capacity of modified hemp fibers was 1.84 mmol of Ag+ ions per gram of fibers. Antimicrobial activity of silver-loaded hemp fibers against different pathogens: Staphylococcus aureus, Escherichia coli, and Candida albicans was evaluated in vitro. Obtained silver-loaded hemp fibers show antimicrobial activity against tested pathogens.

Rotor Cotton Yarns with the Content of Enzymatically Modified Hemp Fibers

The paper reports on a method of preparing hemp fibers for rotor spinning in blends with cotton. Uzbekistan cotton and hemp noils with the linear mass of 5.6 tex and length from 162 mm were used in the experiments. The hemp noils were cottonized in an enzymatic process yielding cottonized hemp fibers with the linear mass of 3.34 tex and 37.4 mm long. Yarn production experiments were made on a BD 200RN rotor machine by using a cotton–hemp sliver with the linear mass of 4.5 ktex. The content of cottonized hemp fibers in the blend with cotton was 30%, 40%, and 50%. Cotton–hemp-blended yarns were produced with linear mass of 32, 40, and 50 tex for the 70/30 blend, 50 tex for the 60/40 blend, and 100 tex for the 50/50 blend. Spinability tests showed that 50% is the limit for the content of hemp fibers in blends with cotton.

Fabrication of nanocelluloses from hemp fibers and their application for the reinforcement of hemp fibers

A novel fabrication has been employed to produce nanocelluloses from natural fibers (hemp) and the developed nanocellulose was then used as “coupling agent” to modify hemp fibers themselves.The size distribution of nano-particles (nanocellulose) was measured by nanoparticle tracking analysis (NTA). Results showed that the oxidation–sonication developed nanocellulose had wider size range (29–281nm) and the average size (100–112nm). Morphologies of nanocellulose displayed a slight difference under field emission gun-scanning electron microscopy (FEG-SEM) and atomic force microscopy (AFM). Mechanical testing showed that the nanocellulose modification could improve the mechanical properties of natural fibers significantly. The modulus, tensile stress and tensile strain of nanocellulose modified hemp fibers were increased by 36.13%, 72.80% and 67.89%, respectively. FEG-SEM and X-ray diffractogram (XRD) were used to reveal the mechanism of nanocellulose reinforcement on natural fibers. FEG-SEM illustrated that the nanocellulose treatment had resulted in an effective distribution of nanocellulose along the stria on the surface of fibers, giving rise to a significant increase in the tensile strength of the treated hemp fibers. The XRD analysis also showed that the crystallinity index of the treated fibers had increased from 55.17% to 76.39%. X-ray photoelectron spectroscopy (XPS) has been used to characterize the surface of fibers and attenuated total reflectance-fourier transform infrared (ATR-FTIR) was carried out to determine the surface chemical reaction in order to elucidate the interface properties and self-modification mechanisms of the hemp fibers.

Application of carbonized hemp fibers as a new solid-phase extraction sorbent for analysis of pesticides in water samples

There is a growing interest in utilization of abundantly available materials, bio-mass or industrial byproducts, as precursors for the preparation of carbon materials. Short hemp fibers, acquired as waste from textile production, were used as low-cost precursor for production of carbon materials as a sorbent in the solid-phase extraction, for pesticide analysis in water samples. Different carbon materials were prepared by carbonization of unmodified and chemically modified hemp fibers. Activation of carbonized materials with potassium hydroxide improves sorption properties of carbonized hemp fibers by increasing the specific surface area (up to 2192m2/g) and the amount of surface oxygen groups. The following parameters that may affect the solid-phase extraction procedure efficiency were optimized: different elution solvents and the pH value of pesticide solution. Extracts were analyzed by liquid chromatography–tandem mass spectrometry technique. For this study pesticides belonging to the different chemical classes were chosen. Obtained results indicate that carbonized and activated hemp fibers could be successfully applied as a solid-phase sorbent for the pesticide analysis in water samples.

Antimicrobial TEMPO-oxidized hemp fibers with incorporated silver particles

In this paper, the preparation of the antimicrobial silver loaded hemp fibers were carried out by selective TEMPO-mediated oxidation, i.e. oxidation with sodium hypochlorite and catalytic amount of sodium bromide and 2,2,6,6-tetramethylpiperidine-1-oxy radical (TEMPO), followed by silver sorption from aqueous silver nitrate solution. The most suitable experimental conditions for the selective TEMPO-mediated oxidation were determined by changing oxidation conditions: concentration of sodium hypochlorite and duration of sorption. The obtained results showed that the maximum sorption capacity (0.703 mmol of silver per gram of fibers) of modified hemp fibers was obtained for the sample modified with 9.67 mmol NaClO per gram of fibers, during 4 hours. SEM microphotographs of the modified hemp fibers with incorporated silver showed uniformly distributed silver particles on the surface of fibers, with isometric shapes and sizes from 10 to 100 nm, despite the fact that silver was sorbed from ionic solution. The antibacterial activity of the TEMPO-oxidized hemp fibers with silver particles was confirmed in vitro against two strains: Staphylococcus aureus (ATCC 25923) and Escherichia coli (ATCC 25922), and the antifungal activity against fungi Candida albicans (ATCC 24433). The best antimicrobial activity of silver-loaded TEMPO-oxidized hemp fibers was showed against strain Staphylococcus aureus.

Mathematical modeling of heavy metal ions (Cd 2+, Zn 2+and Pb 2+) biosorption by chemically modified short hemp fibers

Biosorption, an innovative and low-cost effective method for removal of heavy metal ions from wastewaters, primarily depends on the diffusion of metal ions through the porous structure of sorbent and the resistance effects arise as the result of electrostatic repulsive interactions between ions within the sorbent. Herein, the biosorption of heavy metal ions (Pb 2+, Cd 2+ and Zn 2+) from aqueous solution by lignocellulosic material (chemically modified hemp fibers) was investigated, in order to develop a mathematical model that would describe the phenomenon of different ions transport through porous fiber matrices. Obtained results show that the biosorption process is very fast at the beginning and mainly determined by diffusion of the ions through the porous fiber structure. However, over a period of time the biosorption slows down due to the increase of the resistance to the further transport of metal ions through the fibers (i.e. the electrostatic repulsive interactions between ions into the fibers increase with the increase of the ion concentration in the fibers). The effective diffusion coefficient of metal ions through the fibers, the profile of heavy metal ion concentration in the fibers and the effectiveness of sorption were determined by a mathematical model based on the second Fick's low. Proposed mathematical model is used to optimize the biosorption of heavy metal ions by connecting the model parameters with the fiber performances.

Effect of hemicelluloses and lignin on the sorption and electric properties of hemp fibers

This study investigated the influence of hemicelluloses and lignin removal on the sorption and electric properties, as well as fineness of hemp fibers. Hemp fibers with different content of either hemicelluloses or lignin were obtained by chemical treatment with 17.5% sodium hydroxide or 0.7% sodium chlorite. The sorption properties of hemp fibers were evaluated as moisture and iodine sorption, while electric properties were evaluated as volume electric resistance. Hemicelluloses removal increases in higher extent fiber liberation than lignin removal; the modified hemp fibers were finer up to 12 times in relation to unmodified fibers. Furthermore, hemicelluloses removal increased the moisture and iodine sorption, as well as electric resistance of hemp fibers compared to unmodified fibers, while lignin removal decreased both moisture and iodine sorption, and only slightly increased the electric resistance of modified hemp fibers.

The effects of hemicelluloses and lignin removal on water uptake behavior of hemp fibers

This study investigated the individual influences of hemicelluloses and lignin removal on the water uptake behavior of hemp fibers. Hemp fibers with different content of either hemicelluloses or lignin were obtained by chemical treatment with 17.5% sodium hydroxide or 0.7% sodium chlorite. Various tests (capillary rise method, moisture sorption, water retention power) were applied to evaluate the change in water uptake of modified hemp fibers. The obtained results show that when the content of either hemicelluloses or lignin is reduced progressively by chemical treatment, the capillary properties of hemp fibers are improved, i.e. capillary rise height of modified fibers is increased up to 2.7 times in relation to unmodified fibers. Furthermore, hemicelluloses removal increases the moisture sorption and decreases the water retention values of hemp fibers, while lignin removal decreases the moisture sorption and increases the water retention ability of hemp fibers.

Quality of chemically modified hemp fibers

Hemp fibers are very interesting natural material for textile and technical applications now. Applying hemp fibers to the apparel sector requires improved quality fibers. In this paper, hemp fibers were modified with sodium hydroxide solutions (5% and 18% w/v), at room and boiling temperature, for different periods of time, and both under tension and slack, in order to partially extract noncellulosic substances, and separate the fiber bundles. The quality of hemp fibers was characterised by determining their chemical composition, fineness, mechanical and sorption properties. The modified hemp fibers were finer, with lower content of lignin, increased flexibility, and in some cases tensile properties were improved. An original method for evaluation of tensile properties of hemp fibers was developed.

Surface characteristics of untreated and modified hemp fibers

Natural cellulosic fibers, including hemp, are increasingly being used for composite reinforcement. However, their poor adhesion with synthetic resins limits their use as reinforcing agent. It is generally accepted that interfacial adhesion can be best described in terms of dispersion forces and acid–base interactions. Therefore, there is a need for quantitative determination of acid–base character of natural cellulosic fibers. In this study, acid–base characteristics and dispersion component of surface energy of hemp fibers have been determined using inverse gas chromatography. Effect of alkalization and acetylation on acid–base characteristics has also been examined. The results indicate that alkalization and acetylation make the hemp fiber amphoteric, thereby improving their potential to interact with both acidic and basic resins. Finally, a parallel is drawn between the changes in fiber-matrix acid–base interactions and the actual improvement in the mechanical properties of the composites manufactured using resin transfer molding process. POLYM. ENG. SCI. 46:269–273, 2006. © 2006 Society of Plastics Engineers