Inaug.-Diss.--Hamburg, 1938. / Lebenslauf. eContent provider-neutral record in process. Description based on print version record. "Quellen-und Abkürzungsverzeichnis": p. ix-xii.

One of the recent developments in composite technology in South Africa is the increasing use of natural fiber materials in the manufacture of plastic products. Most of the previous work on natural fiber-reinforced composites has focused on sisal fiber as it was commercially available. In this study, the mechanical and thermal properties of composites made with locally produced hemp fibers, were compared with composites made with hemp fibers produced in France. New commercial polypropylene random copolymer was used as matrix because it can be processed at lower temperatures when compared with other commercial propylene copolymers. The composites were produced by extrusion compounding and were further processed into tensile test bars by injection molding. Up to 30% fiber loading could be achieved. It was observed in all composites that increasing the amount of fiber resulted in an increase in tensile strength, elastic modulus, and flexural strength and a decrease in impact strength. The thermal properties of the composites were analyzed by the thermogravimetric method. It was found that the fiber/PP composites showed excellent properties when compared to fiber and the matrix separately. The addition of hemp fibers shifted the start of the degradation process towards higher temperatures. The results obtained show that the mechanical and thermal properties of South African long hemp fiber composites compare favorably well with the French bleached and unbleached hemp fibers.

Finer count hemp yarn (<20-50 tex) for apparel and smart textiles applications with a minimum number of imperfections cannot be manufactured using the cotton spinning system due to the presence of non-cellulosic materials in the fiber structure. An investigation has been carried out to identify the spinning properties of hemp fibers including strength, length and length variation, single fiber entity, fineness, bending modulus and softness by removing non-cellulosic materials from hemp. Different chemical and enzyme treatments were employed to improve the selected spinning properties of hemp fiber. It was found that bleaching at 95°C for 240 min (min) after scouring removed the largest amount of non-cellulosic materials. After the carding process, the softness of treated samples, with the highest weight loss (%) was found to be improved by about 2.6 times more than the virgin hemp fiber.

The hemp plant is an attractive source of raw material for multiple products. Processing hemp requires the separation of fibre and core components of the plant. Peel tests were conducted for hemp stems to evaluate the strength required to peel fibre from the core. The average peeling force for the Alyssa variety was 0.39 N and that for the USO-14 variety was 0.87 N. The Ising model was implemented to produce a stochast ic model. The simulated peel test behaved similarly to the experimental peel test. A discrete element model (DEM) of a planetary ball mill was developed to predict the energy requirement of grinding hemp for fibre. Hemp grinding tests were performed on variety USO-31 using a planetary ball mill for model calibration purposes. Power draw measurements increased linearly increasing at greater grinding speeds. The DEM approximated power draw with relative error below 10% for grinding speeds below 400 rpm.

Finer count hemp yarn (<20-50 tex) for apparel and smart textiles applications with a minimum number of imperfections cannot be manufactured using the cotton spinning system due to the presence of non-cellulosic materials in the fiber structure. An investigation has been carried out to identify the spinning properties of hemp fibers including strength, length and length variation, single fiber entity, fineness, bending modulus and softness by removing non-cellulosic materials from hemp. Different chemical and enzyme treatments were employed to improve the selected spinning properties of hemp fiber. It was found that bleaching at 95°C for 240 min (min) after scouring removed the largest amount of non-cellulosic materials. After the carding process, the softness of treated samples, with the highest weight loss (%) was found to be improved by about 2.6 times more than the virgin hemp fiber.

The hemp plant is an attractive source of raw material for multiple products. Processing hemp requires the separation of fibre and core components of the plant. Peel tests were conducted for hemp stems to evaluate the strength required to peel fibre from the core. The average peeling force for the Alyssa variety was 0.39 N and that for the USO-14 variety was 0.87 N. The Ising model was implemented to produce a stochast ic model. The simulated peel test behaved similarly to the experimental peel test. A discrete element model (DEM) of a planetary ball mill was developed to predict the energy requirement of grinding hemp for fibre. Hemp grinding tests were performed on variety USO-31 using a planetary ball mill for model calibration purposes. Power draw measurements increased linearly increasing at greater grinding speeds. The DEM approximated power draw with relative error below 10% for grinding speeds below 400 rpm.

Bast fibre reinforced, unsaturated polyester matrix composites were fabricated using non-woven mats of hemp or jute fibre as reinforcement. Composites were also prepared using chopped strand mat glass fibre as reinforcement. The short-term mechanical properties of the laminates were assessed. It was observed that at equivalent fibre volume fractions the stiffness of the glass fibre reinforced material only marginally exceeded that of the two, unmodified bast fibre, reinforced materials. At equivalent fibre volume fractions, however, the strength of the glass fibre reinforced composite was found to be significantly greater than that of the bast fibre reinforced materials. It was noted that in the bast fibre reinforced composites, the onset of non-linear behaviour occurred at relatively low applied stresses. Work of fracture in static three-point flexure and Charpy impact strength tests, indicated that the toughness of the plant fibre reinforced material was as much as an order of magnitude less than that of the glass fibre reinforced material. Fracture mechanics techniques were used to further quantify toughness and confirmed this to be so. Furthermore, these tests indicated that the microstructure of the bast fibre reinforced material should be examined more closely. Microscopy conducted on the fibres revealed that these were often subject to extensive micro-compressive damage. It was postulated that uneven fibre straining characteristics could lead to compromised interfacial properties, which might in turn detrimentally affect the macroscopic behaviour of the composite. A technique known as half fringe photoelasticity was used to investigate the stress-field in the matrix surrounding the fibre defects. It was observed that not only did concentrations of stress occur in the vicinity of these, but also that the shear stress distribution along the length of the fibre was interrupted by the presence of the defects. The implications of fibre defects upon composite properties are discussed.

There is an increasing demand for natural fibres in the textile industry as a consequence of the negative impact of the industry on the environment. Svensk Hampaindustri (SHI) is currently growing hemp in Sweden for its seeds. This leaves residue in the form of hemp stems that could be processed for textile products. Today this residue material is not used for anything, however there is a desire that it could be used for added value. This study investigates the possibility of extracting fibres from the hemp residue mechanically and using them in applications. Hemp, a variety of Cannabis sativa L., is a multipurpose low-input crop cultivated for its seeds, fibres and hurds. Hemp fibre is a bast fibre, derived from the plant’s outer stem tissues. To extract hemp fibres from hemp stems, the first step is to separate the fibre bundles from the other, non-fibrous parts of the stem. This process is done using various mechanical methods. In order to ease the separation, hemp stems are retted. Retting is a biological process that uses enzymatic activities to degrade the pectins and thus making the separation easier. Retting is one of the most considerable challenges towards a wider use of hemp fibres. Water retting offers high fibre-quality but consumes high amounts of water and causes effluents in the wastewater. Dew retting offers a high fibre yield and low labour costs but will result in a lower fibre-quality. Alternative methods that can contribute with a more consistent fibre yield and quality are available, but with an economic uncertainty for the farmers that limits the competitiveness of the hemp fibre. The hemp material provided by SHI was unretted and needed to be broken down by means of mechanical processing in order to extract the fibres. This was done using a domestic blender. The crushed material was then carded using a hand carding machine to achieve oriented and clean fibres. The obtained fibres were then evaluated for their length and fineness. Three different types of nonwoven were made using the hemp fibres: NW1, NW2 and NW3. NW1 consists of 100% hemp, whereas NW2 and NW3 are 80/20 blends of hemp and PLA. NW1 was needle punched, NW2 was thermally bonded and NW3 was manufactured by both thermal bonding and needle punching. The produced nonwovens were evaluated by their air permeability, thermal conductivity, sound absorption, drapability and tensile strength. The results from the study showed that it is possible to extract unretted fibres using mechanical methods. The fibres are quite coarse and therefore more suitable for industrial applications. The different production methods for the nonwovens gave different results which supports the diversity of hemp applications. This study suggests that the residue should be used rather than be disposed of.

The passage of the 2018 Farm Bill created a legal distinction between hemp and marijuana, both of which were previously illegal under federal law. The 2018 Farm Bill federally legalized hemp which became defined as any cannabis or cannabis-derived product containing less than 0.3% Δ9-tetrahydrocannabinol (THC) by dry weight. While marijuana has a high concentration of THC, hemp has a high concentration of cannabidiol (CBD), a cannabinoid similar to THC. Aside from the concentration of specific cannabinoids, hemp and marijuana are macroscopically and microscopically indistinguishable and common forensic testing for cannabis, such as the Duquenois-Levine color test, cannot distinguish between the two. Now that the federal law has been changed, new analytical methods are needed to be able to differentiate between what is legal hemp and what is illegal marijuana. This work employs the use of two analytical methods for the differentiation of hemp and marijuana: Ultraviolet-Visible Spectroscopy (UV-Vis) and Direct Analysis in Real Time-Mass Spectrometry (DART-MS). UV-Vis would be useful for quantitating cannabinoids and is a method that is amenable to field use. Previous studies have shown that fast blue BB salt (FBBBS) complexes with THC and CBD, forming unique chromophores, which can be analyzed by UV-Vis. Seven hemp samples and five marijuana samples were analyzed using this method. The hemp samples displayed two absorbances, the first between 285–290 nanometers (nm) and the second between 469–472 nm. The marijuana samples displayed one absorbance between 292–299 nm. The preparation of the hemp samples consistently produced a light to dark orange color in the sample cuvette while the marijuana samples produced a golden yellow color. Calibration curves were prepared using THC and CBD certified reference materials in an effort to quantitate the cannabinoids in each sample. Reproducibility was an issue and r2 values varied greatly. Differences were seen within the UV-Vis spectra of each sample type but further efforts in quantitation are needed. The use of DART-MS to differentiate between hemp and marijuana is still an ongoing effort. Mass spectra were generated of the previously mentioned hemp and marijuana samples. In almost all analyses, the most abundant ion was m/z 315, the [M+H]+ ion for THC and CBD. A 359 ion was also observed within the samples, which is consistent with tetrahydrocannabinolic acid (THCA), cannabidiolic acid (CBDA) and cannabichromenic acid (CBCA). Subtle differences were seen between the two sample types although it’s difficult to determine how significant these differences are upon visual examination of the mass spectral data. Using Analyze IQ Lab chemometric software, predictive models were built using known hemp and marijuana samples. Preliminary data suggests that the methods built are successful and can correctly classify hemp and marijuana based on their mass spectral differences.

Natural fibers like kenaf, hemp, flax and sisal fiber are becoming alternatives to conventional petroleum fibers for many applications. One such applications is the use of Non-woven bio-fiber mats in the automobile and construction industries. Non-woven hemp fiber mats were used to manufacture plywood in order to optimize the plywood structure. Hemp fiber mats possess strong mechanical properties that comparable to synthetic fibers which include tensile strength and tensile modulus. This study focuses on the use of hemp fiber mat as a core layer in plywood sandwich composite. The optimization of fiber mat plywood was done by performing a three factor experiment. The three factors selected for this experiment were number of hemp mat layers in the core, mat treatment of the hemp mat, and the glue content in the core. From the analysis of all treatments it was determined that single hemp mat had the highest effect on improving the properties of the plywood structure.