Beyond the Flower: Use of the Hemp Stalk for Products and Applications

Introduction

Hemp in the United States and worldwide is a hot topic because of its green nature, sustainability, and zero or low carbon footprint. While most of the hemp world has been flower-centric due to the health benefits of cannabinoids and terpenes, this is only the tip of the iceberg with respect to applications. The entire plant, including flower, seed, stalk, leaves, and root, has 50,000 different uses. For example, the stalk can be used for consumer textiles, industrial textiles, paper and building material. The seeds may be used for industrial products, foods, energy, and body care items. The leaves can be used for foods, animal bedding, mulch, and composting. The roots can be used for organic composting, nutrients, and as a remedy for other health conditions.

Just as any manufactured product requires some type of testing for accuracy, purity, stability, durability, etc., so do hemp-based products. The testing may require several analytical instruments, physical testing machines, x-ray equipment as well as other testing devices. Because of space limitations, and the nearly impossible task of discussing 50,000 possible products, this communication will focus on the stalk, providing an overview of some applications and the instruments needed to ensure finished product quality.

Textiles and Industry Textiles

The hemp stalk consists of an outer layer called the bast fiber and an inner layer of woody pith. The outer layer is used for textiles while the inner layer can be used for fuel, building materials, and animal bedding.

Examples of hemp textiles include woven and knit fabrics, non-woven fiber mats, yarns, and rope. Fabrics can be made of 100% hemp or blended with other fibers such as cotton, flax, or silk. For example, clothing material could be produced from a blend of 30% cotton and 70% hemp fiber. A blended product may be made softer or more durable. There are many advantages of hemp over cotton. Hemp can be grown nearly everywhere and with less oversight whereas cotton only grows in moderate climates and requires more water and pesticides. In addition, one acre of hemp can produce as much fiber as up to three acres of cotton. Hemp is also a stronger fiber and more mildew resistant.

Tensile Testing

Stretchability of Fabrics

Hemp fabrics can be used for T-shirts, dresses, hoodies, underwear, socks, other forms of apparel, as well as for household textiles such as blankets, duvets, towels, tablecloths, and upholstery. Hemp fibers are fine enough to make fabrics with a thread count of 250-300, which is considered percale, a closely woven fine fabric used for sheets. An early harvest will produce a softer fabric. The fabric is very breathable, has high-moisture-wicking abilities, and low heat-retention abilities. The fabrics have a low possibility of pilling where short or broken fibers group together because of abrasion and become tangled in a tiny knot or ball, known as a pill.

Hemp fabrics are considered to have medium stretchability or give. Any of these parameters may be changed by blending with other fibers.

Example of a Universal Testing Machine and Stress-Strain plot

The physical properties of textiles are an interdependent result of fiber type, yarn spinning method, and fabric construction.

A universal test machine measures force and displacement while deforming a sample. They can be configured with many different types of grips and accessories to evaluate the myriad properties of textile products that determine their feel and function, such as fabric stretchability, tear resistance, burst strength, seam strength, and fiber elongation.

Generally, tensile testing of fabrics occurs in two directions: the warp (length) and the weft (width), also referred to as the woof or fill. Shown is an example of tensile testing of a sheet.

UV-Vis-NIR Spectroscopy

Analysis of Natural Illumination and Thermal Insulation

A variety of functional materials, such as fabrics, are being developed for their thermal insulation properties as well as to provide natural lighting. It can be presumed that increasing transmittance and lowering reflectance produce illuminating properties while lowering transmittance and increasing reflectance produce thermal insulation properties. Transmission and reflectance spectra of fabrics can be measured with a UV-VIS-NIR spectrophotometer equipped with an integrating sphere.

Example of a UV-Vis-NIR spectrometer with integration sphere for measuring thermal insulation properties as well as to provide natural lighting

Transmittance Spectra of Fabrics- Black & Red: Designed for Natural Illumination Blue: Designed for Thermal Insulation

Reflectance Spectra of Fabrics -Black & Red: Designed for Natural Illumination Blue: Designed for Thermal Insulation

Analysis of Dye Colors

As any consumer knows, textile color is an important consideration when selecting and purchasing a product. Used in a wide range of fields for material characterization, UV-Vis-NIR spectrophotometers are useful for analysis of dye colors through final product.

UV-Vis-NIR with Double Beam, Single Monochromator for measuring dyes & clothing colors

FTIR and Infrared Microscope

Determination of Pectin Removal Level

FTIR spectroscopy may be used to determine the pectin removal level during the purification process by monitoring the functional groups in the transmission mode. By using the attenuated total reflectance (ATR) accessory, the instrument is capable of differentiating textile fibers by their chemical composition, commonly classified by their origin as natural (e.g. hemp, cotton, linen, silk, wool), regenerated (e.g. viscose hemp, cellulose acetate) and synthetic (e.g. polyester, polyacrylic, polyamide).

A microscope used in conjunction with FTIR helps identify visible and chemical contaminants, breaks in the fiber, and blends of fibers.

Example of a FTIR & Microscope

Chemical Structure of Pectin

X-Ray Diffraction (XRD)

Determination of Crystallinity

During the different stages of chemi-mechanical treatment of the fibers, powder X-ray diffraction (XRD) in transmission mode can be used to determine the crystallinity throughout the process. The goal of the treatment process is to remove amorphous aggregates and increase the crystallinity. Elimination of amorphous compounds, with the increase of crystallinity index, is attributed to the ordered close packing of macromolecules of cellulose in the fibers and strengthening of the hemp fibers.

Example of an XRD

Textile Characteristic and the Instruments used for Measurement

Geotextiles & Construction

Universal Testing Machines

Geotextiles

Geotextiles are soil reinforcements used in environmental engineering and construction projects to prevent erosion, aid in drainage, separate structural layers, and improve vegetation establishment. Due to their long fiber length and strength, hemp fibers can be used in geotextiles in the form of fabric, fiber mats, and nets. In contrast to synthetic plastic geotextiles, hemp is renewably sourced and biodegradable, so it does not contaminate the environment at the end of its useful life. Shimadzu’s AGS-X Series Universal Electromechanical Test Frames are ideal for testing the strength of geotextiles.

Worker laying geotextile used for separation and reinforcement in preparation for a new building

Examples of Universal Electromechanical Test Frames

Hempcrete

Hemp hurd and fibers have found use in several construction materials, including concrete, insulation, and particleboard. When hemp hurds are incorporated to lime-based cement, they create a renewably sourced, lightweight, and insulating building material that can replace concrete and synthetic insulation in some applications. Hemp stalk materials are also possible replacements for wood chips in fiberboard and particleboard materials. Typical tests for construction materials include compression and bending tests, and evaluation of changes in physical properties due to environmental exposure. Hydraulic test frames can achieve the forces required for testing high-strength construction materials, and the software includes a concrete test control program.

Hempcrete Building

Hydraulic test frames compression for hempcrete

Compression Testing of Hempcrete

High Speed Video Camera (10M Frames/Sec)

Natural Fiber Composites

Universal Testing Machine

Tensile Testing

Natural fiber composites combine plant fibers, such as hemp, with a polymer matrix to create materials with improved rigidity and strength and decreased weight. Composites made with natural fibers have potential advantages over glass and carbon fiber reinforcements in many applications due to the right balance of weight, cost, and performance in addition to generally having much lower energy of production.

They are already widely used in the automotive industry for interior panels such as doors and trunk liners and are expected to be incorporated into more components as their properties are improved. Bending and shear testing are important because composite strength can vary depending on the direction that force is applied. Natural fiber composites may also be more sensitive to humidity and temperature, so performing physical testing in thermal chambers is necessary.

Car Door Liners Made of Hemp

Car Trunk Liners Made of Hemp

Universal Testing Machine 3-point bending

Results of a 3-point bending test performed on a composite material to determine flexural modulus

Thermal Analysis and Capillary Flow Technology

Thermal properties of composite resins

A variety of thermal properties of composite resins and industrial chemicals can be determined using thermal analysis instruments (TGA, DSC, TMA, and DTG) and Capillary Flow Technology (CFT). These properties include glass transition temperature, degradation or melting temperature, purity analysis, and curing behavior.

Shown below is a DSC measurement of a hardening reaction of an epoxy resin at various points of heat treatment. As the reaction progresses, the glass transition temperature increases and the enthalpy of reaction decreases.

DSC measurement of a hardening reaction of an epoxy resin at various points of heat treatment (left) and DSC, TGA, and TMA

Industrial X-Ray Computed Tomography (CT)

Internal structure and features

Industrial X-Ray CT systems provide detailed visualization of the internal structure and features of an object. Scanning composites can identify fiber position and alignment, calculate volume fraction of different components, and identify the size and distribution of pores. Powerful color processing software enables observation and statistical calculations of different internal regions. CT scanning is also a useful tool for identifying cracks, voids, and disconnections for failure analysis.

This CT scan of the fracture fiber composite illustrates areas of delamination and cracking (left), and example of an X-Ray Computed Tomography (CT) instrument.

Paper Products

Tensile Testing, Particle Size, and Mass

Paper Parameters

Hemp paper from the stalk can be used for printing, newsprint, packaging, cardboard, and other paper products. Paper products can be made of the long bast fiber or the hurd (or pulp). The different parts of the stalk may have different applications. The fiber bast paper has been reported to be thin, tough, brittle, and rough while the hurd has been reported to be thicker, easier to make, not as strong, with more daily applications. Depending on the source of information, dried hemp has been reported to have between 50-85% cellulose, the main ingredient in paper, while trees are in the 30-50% range. Therefore, the other 50-70% of chemical compounds from trees have to be removed. Relatedly, hemp has lower concentrations of lignin, which must be removed during the process of making paper products. The lignin concentrations are 5-24% and 20-35% for hemp and trees, respectively. Hemp paper can be bleached with hydrogen peroxide instead of the toxic chlorine or dioxin chemicals used with paper from trees.

Hemp reaches maturity in 3-4 months while trees require 20-80 years and, in addition, hemp has four times more fiber than a forest using the same landmass. Thus, hemp paper can be produced at a much faster rate. It also has been reported that hemp paper products can be recycled eight times, while tree products can only be recycled less than half the number of times.

While on-line sensors may be available to measure some production parameters, lab-scale method development may require laboratory instruments. Some parameters measured are weight, moisture profile, ash content, color, brightness, smoothness, gloss, coat weight, formation, porosity, fiber orientation, surface properties, tear strength and opacity. For example, a universal tester could be used for the determination of breaking strength, breaking length, tearing strength on the long and short side, elongation, fold resistance, and more. Analytical, top-loading, and moisture balances are available to calculate weight and moisture profiles.

In the paper industry, coatings, fibers, fillers, sizing agents, and other items affect a paper’s properties, such as brightness, color, gloss, and opacity. A particle size analyzer is ideal for this application.

Energy

High-Performance Liquid Chromatography (HPLC)

Bioethanol

The 2007 federal legislation that encouraged production of biodiesel in the United States has also increased production of ethanol in an effort to offset dependence on fossil fuels and reduce carbon dioxide emissions. The cellulosic material in hemp can be converted into sugars and fermented into ethanol to be used as a supplement in gasoline, much as has been done with corn and soybean biomass.

Careful attention must be paid to the fermentation process to guarantee its efficiency and the purity of the final ethanol product. High-performance liquid chromatography (HPLC) is an ideal method for monitoring the conversion of sugars to alcohol during fermentation.

HPLC and chromatogram of sugars to ethanol during fermentation 34 hours after the process began. Peaks are 1) DP4+ (oligosaccharides with ≥4 degrees of polymerization), 2) DP3 (oligosaccharides with 3 degrees of polymerization), 3) Maltose, 4) Glucose, 5) Lactic acid, 6) Glycerol, 7) Acetic acid, 8) Ethanol

Gas Chromatography (GC)

After fermentation is complete, the produced ethanol must be denatured to ensure that it is not taxed nor used for human consumption. Following test methods such as ASTM D5501, which specifies GC-FID, allows for the determination of the ethanol content in ethanol denatured with methanol or gasoline.

GC-FID and chromatogram methanol and ethanol content in a fuel ethanol denatured with gasoline by ASTM method D5501.

Conclusion

For many, the value of hemp has been focused primarily on the flower and seeds. However, the other parts of the plant, specifically the stalk, leaves, and root, also offer tremendous value and growth potential. Due to space limitations, writing about all the potential uses of hemp and hemp-based products is not a feasible objective so this communication focused solely on applications related to the stalk. Future communications will address applications related to other parts of the plant.

Using hemp for industrial products has its challenges. For example, it’s not easy to disrupt industries with hundreds or thousands of years of proven supply chains. Food-grade plastics must be FDA compliant and USDA certified to ensure no hazards are in the plastics requiring new testing for new products. Current agricultural and processor equipment will need to be modified for hemp so that, in a single stage, the crop is divided into stalks, seeds, and leaves. Fiber will require big processing centers, as with corn. In addition, processing hemp for paper or textiles differs from how cotton is processed.

Finally, hemp-based products, like the products they replace, will require testing to ensure safety, reliability, accuracy, purity, stability, durability, etc. This testing may require several analytical instruments, physical testing machines, x-ray equipment, and other devices.

Despite these challenges, the benefits of this green, low-carbon crop are clear. And with the proper commitment, the entire hemp plant offers long-term potential for sustainable growth.

Learn more at www.GrowYourLab.com

This content is provided as a membership benefit to our valuable business level members. Due to several factors including the variances in state hemp laws and the differences in interpretation of federal law, NHA makes no warrants of the legality, efficacy or safety of any product, service or statement made by any third party.

We encourage all members and the general public to do their own due diligence on any business or product, and understanding their state’s and federal laws, before choosing to purchase any product or contracting for any service.

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