for their high sensitivity, easy signal collection, fast response, and simplicity of design, which are favored in diverse fields. [2,5] Consequently, the requirements for strain and pressure sensing materials are also highly proliferating. [6] Hydrogels, a class of 3D networks formed by the cross-linking of hydrophilic polymer chains within an aqueous microenvironment, which not only exhibits high flexibility, excellent stretchability, deformation restorability, and self-healing ability, but also possesses good biocompatibility, biodegradability as well as non-toxicity, making them a promising material for flexible actuators, soft electronics, wearable sensors, and implantable medical devices. [7,8] Polyvinyl alcohol (PVA), as the largest water-soluble polymer in the world, has been widely used in the fabrication of physically crosslinked hydrogels through freezing-thawing process. [9,10] Due to their merits of safety, high flexibility, transparency, and mild and scalable preparation, PVA hydrogels are ideal candidates utilized for portable wearable sensor compared to other materials. [11] Cai and co-workers reported an extremely stretchable piezoresistive strain sensor based on various self-healing PVA hydrogels such as carbon nanotubes (CNTs), graphene, and silver nanowire/PVA hydrogels, which could effectively monitor multifarious human motion when used as wearable sensor. [12] Hu et al. successfully prepared a composite conductive hydrogel combining PVA, polyaniline and glycerin, which demonstrated high sensitivity of 2.14, fast response time (230 ms), and long cyclic stability as wearable sensors. [13] Building multiple network structure is a desirable method to strengthen mechanical performance by exerting synergistic effect. [11,14] Sodium alginate (SA) is a common natural polysaccharide with extraordinary biocompatibility and biodegradability, which is extensively used in food, pharmaceutical preparations, and wastewater treatment. [15] SA is capable of reacting with multi-valent metal ions to form hydrogels via crosslinking reaction. [7] However, the weak strength and instability are the main disadvantages of SA hydrogels, greatly limiting its application in various strength-demanding fields. [10,16] Accordingly, the blending of PVA and SA is properly adopted to form double physical crosslinking composite hydrogels, which can effectively improve the strength and stability of individual hydrogels. [17] As verified in several literatures, Zhang and co-workers synthesized one interpenetrating network hydrogel based on Flexible and wearable sensors are fast establishing their status as go-to devices for human motion detection. A bacterial cellulose-reinforced hydrogel is fabricated through a facile and scalable freezing-thawing process with Ca 2+ crosslinking for strain and pressure sensing. Polyvinyl alcohol/sodium alginate/bacterial cellulose/modified carbon nanotube and carbon black hydrogels assembled as piezoresistive strain sensors and capacitive pressure sensors exhibit an excellent synchronicity betw...

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Over the last several decades, Cannabis sativa L. has become one of the most fashionable plants. To use the hemp potential for the development of a sustainable textile bio-product sector, it is necessary to learn about the effect of the processes creating hemp’s value chain on fibre properties. This review presents a multi-perspective approach to industrial hemp as a resource delivering textile fibres. This article extensively explores the current development of hemp fibre processes including methods of fibre extraction and processing and comprehensive fibre characteristics to indicate the challenges and opportunities regarding Cannabis sativa L. Presented statistics prove the increasing interest worldwide in hemp raw material and hemp-based bio-products. This article discusses the most relevant findings in terms of the effect of the retting processes on the composition of chemical fibres resulting in specific fibre properties. Methods of fibre extraction include dew retting, water retting, osmotic degumming, enzymatic retting, steam explosion and mechanical decortication to decompose pectin, lignin and hemicellulose to remove them from the stem with varying efficiency. This determines further processes and proves the diversity of ways to produce yarn by employing different spinning systems such as linen spinning, cotton and wool spinning technology with or without the use of the decortication process. The aim of this study is to provide knowledge for better understanding of the textile aspects of hemp fibres and their relationship to applied technological processes.

Flax and hemp fibers are known as textile raw materials with pro-health properties. This paper presents results of research aimed at investigating the antioxidant activity of the fibers in order to explain a mechanism for the favorable influence of textiles made of these fibers when in contact with human skin. The study presents a new approach in evaluation of textile fibers in terms of their inherent pro-health properties. Antioxidant properties of flax and hemp fibers were tested with the use of FRAP and DPPH methods. The content of phenolic acids: syringic, sinapinic, p-coumaric and ferulic acid was determined with the use of HPLC. The results proved that the antioxidant activity of the tested fibers depends on a type and variety of fibrous plants, a method of fiber extraction and subsequent stages of preliminary processing of the fibers. Both decorticated flax and hemp fibers showed higher antioxidant activity in comparison to the fibers obtained with other extraction methods, while decorticated flax of different varieties presented the highest value of the FRAP. Wet methods of fiber extraction and processing caused reduction of phenolic acids content and significantly lower values of the FRAP and DPPH.

This article presents an evaluation of bast fiber properties conditioned by the selection of a retting method in terms of meeting requirements for the final application of the fibers as composite reinforcement. Two different methods of fiber extraction were used in the experiment: dew retting and osmotic degumming. The fibrous material was extracted from flax (Modran variety) and hemp (Bialobrzeskie variety). In addition, retted kenaf fibers (from China) were evaluated for the comparison of fiber properties. The properties of the retted and degummed fibers were evaluated according to relevant valid standards regarding color, linear mass, breaking tenacity, aspect ratio, microscopic images and chemical composition, which included the determination of wax and fat, cellulose, hemicellulose, lignin and pectin content and the thermogravimetric analysis coupled with Fourier transform infrared spectroscopy technique. The Attenuated Total Reflection FTIR spectroscopic technique was used for the characterization of the fibers. Also, fogging and volatile organic compound (VOC) emissions were tested in order to evaluate the suitability of the bast fiber for composite formation. The results of the study proved that osmotic degumming applied for bast fiber extraction improves significantly the fiber quality in terms of color, odor, aspect ratio and VOC emission. The aspect ratio of osmotically degummed flax fibers increased by about 46% and hemp fibers by about 22% in comparison with dew-retted fibers. VOC emission of osmotically degummed hemp decreased by about 35%, but in the case of flax fibers, increasing of VOC has been observed. For this reason, osmotically degummed fibers can be recommended as more suitable for composite reinforcement.

After a long break, Spanish broom gained interest as a natural, sustainable and renewable fibre for textile and technical applications. This paper describes the characterization of Spanish broom fibres ( Spartium junceum L.) in comparison to the flax fibres ( Linum usitatissimum). Spanish broom fibres were obtained by two different methods of maceration and some of the most significant chemical and physical properties of tested fibres are reported. Scanning electron microscopy has proven to be a useful tool for the determination of morphological characteristics of elementary and technical fibres. Other physical-chemical properties of fibres were determined by infrared spectroscopy (FT-IR), thermogravimetric analysis (TGA), fineness and tensile strength methods.