Development of Hemp Fibers: The Key Components of Hemp Plastic Composites

Abstract

Plant fibers in general and hemp fibers in particular have great prospects for their use in various innovative applications such as ecological, biodegradable, and renewable resources with unique properties. Such properties together with the increased strength due to high-cellulose content and specific morphological parameters are widely used to produce plant fiber-based plastic composites. The properties of plant fibers that may influence the properties of composites depend on crop processing, but the basis for them is provided during fiber development in planta. It is known that two types of bast fibers are developed in the hemp stem: primary fibers formed from procambium cells and secondary fibers that originate as a result of cambium activity. Both types of fibers may significantly vary in their yield and quality depending on the variety and growth conditions. Differences in the anatomical and morphological characteristics of the two types of hemp fibers, together with peculiarities in the composition and architecture of cell wall, influence the technical parameters of the raw material quality. Based on our study of both primary and secondary fiber development in hemp stem that was focused on the two key stages, intrusive elongation and deposition of thick cell wall layers, we suggest the set of parameters that can influence the quality of the mature fibers and trace their biological origin.

Valorization of Byproducts of Hemp Multipurpose Crop: Short Non-Aligned Bast Fibers as a Source of Nanocellulose

“…Due to the removal of the middle lamella, the individual fibers composing the bundles became clearly visible, but did not separate much further ( Figure 4 b), as even high concentrations of NaOH have been reported to not be able to completely remove all the lignin and pectin cementing the bundles [ 42 ]. The estimated widths of the individual fibers, 3 μm to 20 μm, were consistent with those reported in the literature [ 42 , 43 ].…”

Extraction of cellulose fibers from flax and hemp: a review

“…Thus, primary fibers appear in the early stages of plant development and run through the plant length, while secondary fibers appears in the later stages and are found towards the bottom parts of stems, located in a zone between the woody core and the primary fiber bundles. Fibers also occur in the xylem tissue regions, or the woody cores (termed ''shive'' and ''hurd'' in flax and hemp respectively), but they are far shorter, more heavily lignified, and do not occur in bundles (Amaducci and Gusovius 2010; Chernova et al 2017). The primary and secondary fibers are also termed as the ''extraxylary'' fibers, since both occur outside xylem tissue regions in the plant, and fibers from the woody cores are termed ''xylary'' fibers.…”

“…That results in the typical structure of fiber bundles, that of tightly packed overlapping elementary fibers. The degrees of intrusion, and thereby the thickness of fiber bundles, are sensitive to environmental stresses and thus variations in them may be observed along the stem length depending on changing climatic conditions during plant development (Chernova et al 2017). A schematic illustration of the intrusive growth is shown in Fig.…”

“…Secondary fiber cells (which occur only in hemp) are initiated at the cambium, with the first cells appearing approximately halfway along the stem length followed by a progression in cell appearance towards the direction of the root (Chernova et al 2017). They appear in the course of radial stem growth in sections where elongations have already ceased, and thus secondary fiber cells elongate only through intrusive growth.…”

“…MDPI (Basel, Switzerland) in the SCW layers. Their angle of orientation to the fiber axis (microfibril angle, MFA) differs: in the PCW, it varies over a wide range; in the S1 layer it is in the range of 60-80°or higher; while in the S2 layer the microfibrils are nearly coaxial to the fiber with MFA of about 8-10°in flax and about 2.7°in hemp (Baley et al 2020;Chernova et al 2017;Goudenhooft et al 2019). The S3 layer is essentially nascence of the S2, and often not visible in mature fibers.…”