Application of Natural (Plant) Fibers Particularly Hemp Fiber as Reinforcement in Hybrid Polymer Composites - Part I. Origin of Hemp and Its Coming into Prominence, Cultivation Statistics, and Legal Regulations

ABSTRACT This paper presents a multi-aspect analysis of whether it is feasible and practical to process natural (plant) fibers into fabrics and mats as homogeneous or hybrid reinforcement in polymer composites for use in various industrial sectors. The current, stringent environmental rules of safe recycling and/or disposal of worn or damaged products at the end of their lifetime require new reinforcing materials to be used in polymer composites that need to meet the criteria of energy and material recycling. The paper comparatively analyzed chemical compositions of some selected (plant) natural fibers and compared their physical and chemical properties relative to commonly used synthetic (mineral and carbon) fibers. The world production of respective species of natural fibers has been presented. Industrial hemp was singled out as the possible quality reinforcement to be used in polymer composites in Poland and in Europe. The paper also provided a broader historical perspective of hemp’s importance for mankind over the past 28 thousand years. Hemp’s history and its impact on human development have been discussed. Finally, the paper compiled knowledge on industrial hemp use, agriculture, and processing as well as its current legal status in Poland and abroad.


Introduction
Due to sustainable development requirements, materials used to make technological products have to be replaced by lighter, more durable materials and systems that can meet the most stringent environmental standards.The issues of utilization and/or recycling of recreational boats at the end of their useful life CONTACT Andrzej Bledzki andrzej.bledzki@zut.edu.plFaculty of Mechanical Engineering and Mechatronics, West Pomeranian University of Technology,al. Piastow 19,Poland made with fiber-reinforced polymers (FRP) that include glass fiber (GF) and carbon fiber (CF) have been identified in many European Union projects.These include Horizon 2020 Framework Programme, known as H2020 and implemented 2013-2020, that postulated universal design of technological processes based on technology readiness levels (TRL), implementation of sustainable production in the ecological sense, and recycling of existing products aiming at conservation of the natural environment.Additionally, in December 2015 the European Commission adopted a package of circular economy promoting innovative solutions that would ensure a high level of environmental protection.
The European strategy for plastics adopted on January 16, 2018, in Strasbourg, France, was geared toward protecting the environment and supporting the well-being of its citizens.It aimed to achieve its goals through strengthening the role of European industry, boosting innovation in design, production, application, and recycling of products in the EU (European Commission EC Communication 28/2018 2018).To meet the criteria set by international conventions and regulations regarding environmental protection, safe recycling, and/or utilization of end-of-life (EOL) products, cloth and glass mat reinforcing composites that have been used for years must be eliminated.Over the last several decades, technological development of polymer materials, including polymer composites, has changed almost every branch of economy.
Polymer matrix composites have applications in a number of industrial sectors, including chemical, automotive, machine, building materials, electronics, aviation, ship-building, arms and defense, and finally in space technology.The 1980s and 1990s witnessed the emergence of natural (plant) fiber-reinforced polymers that could be safely recycled and/or utilized.Such polymers are made using commonly available plant sources that occur all over the world.Wide-ranging research on the use of natural (plant) fibers as replacement for glass in reinforcement of polymer matrix composites confirms the initial assumptions.Biomaterials containing jute (JF), kenaf (KF), industrial hemp (Cannabis sativa L.) (HF), flax (FF), ramie (RF), abaca (Manila hemp) (ABF), sisal (SIF), and cotton (COF) fibers were used to produce car components in the US and Europe, mainly in Germany.End-of-life structural composites (e.g., wind turbine blades, car bodies, and interior components) are expected to be easily utilized with energy recycling methods.A wide range of biocomponents used to reinforce structural composites enables generation of required (tensile, bending) strength properties, including impact resistance, hardness, and density, not to mention being weather-proof.Additionally, composites can be easily shaped to fit the requirements of the final product.There has been a gradual increase in the quality of complex composite materials due to easy access to source components, novel production technologies, and new scientific approaches.Jute, flax, industrial hemp, or cotton fibers tend to replace cloth and glass mats as alternative reinforcements, thus being part of the EU environmental recommendations, requirements, and policies.

Comparative analysis of natural (plant) and synthetic fibers used in composite materials
Not only synthetic but also some natural (plant) fibers have been increasingly used for the production of plastics for various industrial applications.As the commonly used cloth and glass mat reinforcement materials cannot undergo energy recycling, the strict environmental regulations have forced researchers to focus on natural, mainly plant-based fibers as alternative reinforcement for plastics/ composites.There are approximately 2000 fibrous plants and fiber crops, half of which can be utilized.
In the current research, some of them have been singled out as possible replacements of current reinforcing materials.These include bast (jute, kenaf, industrial hemp, flax, and ramie), leaf (abaca/ manila, sisal), seed (cotton), fruit (coir), and grass (bagasse, bamboo) fibers.
Some fibrous plants that are abundant in different regions of the world are presented in Figure 1 Their natural habitat in a specific geographical region of the world is a significant criterion in terms of the proper selection of a fibrous plant and its further industrial and technological applications.Examples of fibrous plants abundant in different regions of the world (Scheibe 2022): 1. Bast fiber/Fibrous plant -natural habitat: 1.1 Jute -Tropical marine and monsoon climate of South-East Asia, Northern Africa (mainly Egypt), and South America. 5. Grass and cane fiber/Fibrous plant -natural habitat: 5.1 Sugar cane (Bagasse) -Tropical and subtropical climate, in countries located between 30 degrees of north and south latitude.5.2 Bamboo -Tropical and subtropical regions of Asia, both America, Africa, and Australia.
In the context of accounting for regions with abundant fibrous plants in the world, it is necessary to consider the following factors that can affect their cultivation: (a) Environmental: the quality (fertility) of soil, climate, natural topography, water in the soil and surface water obtained from rainfall (b) Other factors: the level of efficiency and profitability of production, saturation with machines and equipment, purchase of agricultural products (agricultural policies of the government), taxes, bank loans, tax relief system, the application of chemical agents (artificial fertilizers), the size of arable land, the structure, size and ownership type of farms, the age, gender and education structure of farmers, the development of industrial sectors that cooperate with agriculture (electrical machinery products, chemical industry), the development of food industry (farmers' customers), and export/import of either raw or processed crops.
In the context of European (Central Europe) climate conditions, there are two fibrous plants that can be taken into account.First, flax that is abundant, grown in industrial scale, expensive to cultivate and to produce.Second, industrial hemp (Cannabis sativa L.) which is relatively cheaper to grow and produce.
It should be noted that the properties of hemp, also known as fibrous or industrial hemp -(Cannabis sativa L.) presented in this paper, compared to other fibrous plants, do not apply to wild hemp (Cannabis ruderalis), and -in particular -to cannabis (Cannabis indica) containing more than 0.3% Δ9 THC.
Cellulose is the main component of plant fibers for technological applications and is fundamental in the use of end products.The first information on this subject was recorded in the 1920s, after research on plant fibers: jute, flax, cotton, and hemp, carried out mainly in Europe (mainly in Germany, Great Britain), the United States, and Asia (India) (Bledzki and Gassan 1999;Faruk et al. 2012;Kozlowski 2012;Lee, Kim, and Yu 2009;Madsen and Lilholt 2003;Mwaikambo andAnsell 1999, 2001;Thomason et al. 2011;Timmel 1957).The results of research on the properties of selected fibrous plants, conducted in the last decade in various research centers around the world, show, among others, works after 2015 (Ankit and Pramendra 2018;Mohajerani et al. 2019;Sanjay et al. 2016;Sanjay, Arpitha, and Yogesha 2015).Table 1 shows the chemical composition of plant fibers per weight percentage to present the contribution of respective fiber components.
It should not be forgotten that since the mid-1950s, research has been carried out in many different research centers around the world on the properties of cellulose for industrial applications and methods of modifying plant fibers, which are a potential material for use as reinforcements in polymer composites (Bledzki, Reihmane, and Gassan 1996;Bolton 1995;Brouwer 2000b;George, Sreekala, and Thomas 2001;Keller 2003;Mueller and Krobjilowski 2003;Nabi Saheb and Jog 1999;Pervaiz and Sain 2003;Pickering et al. 2007;Schmidt and Beyer 1998;Timmel 1957;Wambua, Ivens, and Verpoest 2003;Wötzel, Wirth, and Flake 1999).
Analysis of respective chemical components of plant fibers, particularly cellulose, cited in the literature starting from the second decade of the 21st century (Das and Kalita 2014;De Rosa, Santulli, and Sarasini 2010;Faruk et al. 2012;Manaia, Manaia, and Rodriges 2019;Ramamoorthy, Skrifvars, and Persson 2015;Shah 2013;Shahzad 2011;Srinivasa et al. 2011;Tri-Dung 2018) confirms that the location of plant cultivation in various parts of the world has a dominant impact on size distribution of chemical compositions.
The presented types of fibers have properties that can be rationally used for designing and production of composite materials suitable for diverse environmental conditions.To learn about the possible applications of a given fiber, used as reinforcement of polymer composite instead of a synthetic fiber, physical and mechanical features of some selected fibrous plants were thoroughly analyzed (Bledzki and Gassan 1999;Bledzki et al. 2014;Brouwer 2000a;Das and Kalita 2014;Faruk  Bearing in mind the economic aspects of cultivation of flax and hemp, analysis of their agricultural, ecological, and economic aspects, detailed analysis of physical and mechanical properties of their fibers, size of production (thousands of tons), price of raw material (USD/1 t), energy required to produce them (GJ/1 t), technological demands of E type glass fibers, one plant has been selected that meets all the above requirements.It is fibrous hemp (Cannabis sativa L.), also known as industrial hemp, which is common in the world, Europe and Poland (Table 3).
Commonly used synthetic fibers, i.e., mainly glass, less frequently carbon, which are used to reinforce polymer matrix composites have different physical and mechanical properties.They also differ in the type of deformation they can undergo.The final properties of a composite produced on the basis of some fibers are not the sum or average of successive features of its individual components.The same applies to a situation when synthetic fibers are replaced by natural (plant) fibers.When a new material is introduced into automotive or ship-building industry, it must meet a number of criteria, including low mass (density), high impact absorption (determined in crash/collision tests) (Bledzki et al. 2014), low price, and be fully recyclable energetically.In every structural composite, the role of a matrix is to protect reinforcement from an external point and mass forces being loaded onto it to be able to keep the designed shape.Similarly, the role of reinforcement material is to give a composite some required mechanical properties and to strengthen the matrix along the main directions of applied forces and mass loads.Table 4 shows a comparative analysis of chemical compositions of some natural (plant) fibers and their physical and mechanical properties compared to commonly used (glass) mineral fibers in terms of their ecological potential to manufacture composite materials and to be safely disposed of.

Poland's resources of natural (plant) fibers and their applications
Figure 2 shows the latest data for world natural fiber production in 2020, 2021, and 2022 est. in thousands of tons.No details about their quantitative use in different industry sectors were given.The world's statistic for 2022 has not been published yet (DNFI 2022).
Over the past decade, scientific research and technological and industrial centers all over the world have shown more interest in the application of so-called "green" raw materials in many sectors of economy.New and modern production plants that implement high-tech innovation perceive fibrous plants as the future source of fibers that can be used to produce environmentally friendly new materials.Over the last 30 years, natural (plant) fibers have been mainly used in the automotive industry.A total of 20 car manufacturers from all over the world, including American (Ford, General Motors), European (Audi, BMW, Mercedes-Benz, Volkswagen, Peugeot, Renault, Rover, Volvo, Fiat, and Citroen), and Japanese (Nissan, Toyota) have been successfully using jute and hemp fibers (Tri-Dung 2018).Due to climate conditions, jute and hemp are grown chiefly in South-East Asia (in China (provinces Anhui, Guangxi, Heilongjiang, Henan, Shanxi, Shaanxi, Shandong, Sichuan, Yunnan, Inner Mongolia Autonomous Region (IMAR), and other provinces and autonomous regions), India, and Pakistan), South America, North America (US, Canada), and Europe (mainly France, Romania, and Baltic States).Tropical plants, such as abaca and kenaf, are grown in the Philippines, Malaysia, and India.Sisal is cultivated in North America (US -Florida), South Africa, and Brazil.
There are two common fibrous plants in Europe and Poland: flax and hemp.Their prospective industrial applications should consider: (1) If their cultivation involves any burden (how many times they need to be sown and harvested, amount and diversity of necessary fertilizers used, and total cost of farming); (2) If it is easy to obtain fibers (complication of technological processes, cost of producing fabrics, and mats); (3) Their physical and mechanical properties  Research shows that hemp fibers can have the most diverse application in many different industrial sectors.Following analysis of fibrous plants and fiber crops regarding their chemical composition, world production  volume, and natural habitat, hemp was selected as the plant of choice for Poland.Apart from hemp fibers used as sewing material, its fiber is used in technological application in many industrial sectors.During decortication of hemp, shives are the by-product.Hemp shives are used instead of wood in construction, furniture industry, and as energy source.Approximately 25% of fibers and 75% of shives can be obtained from processing of hemp straw.One hectare of hemp can produce 15 tons of biomass, which is three times more than other grain crops (Mańkowski, Kołodziej, and Baraniecki 2014).According to statistic figures published in some European countries, e.g., France and Romania, biomass produced from 1 ha of hemp is approximately 10 to 12 tons.The global interest of various industrial applications of hemp (mainly in South-East Asia) was reflected in the first Asian Hemp Summit, held on 1 to 2 February 2019, in Gokarna Forest Resort in Kathmandu, Nepal (Hemptodey 2018).The summit confirmed that although industrial hemp fibers obtained from hemp stems are not useful for pharmaceutical and textile industries, they can be used well as reinforcement in polymer composites due to their low density, strength properties, and low prices, compared to traditionally used glass fibers.Almost 100% of industrial hemp fibers can be utilized with energy recycling method.One year later (5 February 2020), a subcommission for bioeconomy and innovation in agriculture had a meeting in Polish parliament (Subcommittee for bioeconomy and novelty matters in agriculture in Seym of Poland, Regulation 2/2020 2020).The main agenda topic was the current state and future of hemp farming and processing in Poland.The commission highlighted the importance of hemp as an innovative solution for Polish agriculture and industry.

Genesis, importance of hemp, and its influence on development of civilization
Hemp (Cannabis sativa L.) also known as fibrous or industrial hemp belongs to the family Cannabaceae, one of the most evolved plants on the planet.It has existed for tens of thousands of years.From time immemorial, hemp has been used by people making itself a human friendly plant.
Cannabaceae family consists of Cannabis indica and wild growing Cannabis ruderalis.As shown in Figure 3, hemp varieties have different stem height and leaf sizes.Like no other plant on the planet, hemp has the ability to fit to all land conditions in every climate, regardless of sunshine exposure, water, and mineral composition of soil.
Scientists examining geological and archaeological sites in Northern China and Southern Russia found the earliest traces of hemp pollen.According to scientists, hemp emerged in the Tibetan Plateau close to Qinghai Lake (surface elevation 3,196 m), also known as Koko Nor, which is an alkaline salt lake of tectonic origin (Figure 3).
Figure 4 presents a world map showing the spread of all varieties of hemp (Cannabaceae) (Warf 2014).Analysis of archeological records, artifacts, and available literature give a broad idea of hemp's ancient history (Table 5).Approximately 14 000 BC, people inhabiting South-East Asia started hemp cultivation on a larger scale although being unable to distinguish its varieties.For tens of hundreds of years, hemp was used mainly for medicinal and religious purposes as well as for practical functions in the household (food source, material for ropes, and primitive fabrics).

Current legislation of industrial hemp farming and processing in Poland and in the world
The hemp species Cannabis sativa L. is distinctly different from Cannabis indica, from which marijuana is made.The former grows to be approximately three times taller (maximum height of over 2.5 m and sometimes even 5.0 m) with leaves in inflorescence being much thinner, while the latter forms wider, smaller bushes.Hemp has lower contents of Δ 9 tetrahydrocannabinol (Δ9 THC), considered in many countries illegal, therefore hemp farming is possible in most EU countries, including Poland.Industrial hemp should have less than 0.2% Δ9 THC in Poland, and growing other species of this plant in this country is illegal (Spychalski et al. 2013)  research purposes and since 1998 for commercial use of industrial hemp with Δ9 THC below 0.3%).Although the licenses are free of charge, each farmer must pay for Δ9 THC tests conducted on their plants and present a certificate of clean criminal record (Janusz 2017).In the US, where the world's largest importer and consumer of hemp products, hemp farming is not illegal.It is, however, strictly controlled and requires a permission from Drug Enforcement Administration (DEA).If a farmer does not have the required permission, all crop will be confiscated and severe financial penalty will be imposed (Janusz 2017).In the second half of 2018, first the Senate and House Agriculture Committee and then the Congress and House of Representatives approved a bill regulating hemp farming.On 20 December 2018, the US President signed the 2018 Hemp Farming Act (Pamplin 2018), thus making it valid legislation.The act removed hemp from the forbidden crop list (on the federal level) and therefore gave the green light for hemp cultivation in states where it was unregulated.
Mexico, Latin, and South American countries have been trying to regulate their legal and administrative rules of legal hemp production.Unfortunately, most regulations are inconsistent, and they significantly differ from each other (Hempking 2020).

Conclusions
All types of technological products, and particularly spatial systems made with structural polymers multi-layer reinforced with mineral (glass) fibers (cloth and mats), at the end of their life become unwanted waste which is not biologically degradable and ends up in landfills.This is because the materials used for these products cannot undergo degradation.Partial or complete replacement of commonly used mineral (glass) fibers with natural plant fibers for production of composite polymers can significantly improve compliance with strict environmental protection requirements through their total utilization, e.g., with energy recycling.
In the light of the currently applicable stringent regulations on preventing degradation and environmental protection, it is possible to replace non-ecological reinforcement made of glass fibers with ecological reinforcement made of natural plant fibers, with particular emphasis on HF, in polymer structural composites.
Therefore, it is important to be able to implement the next generation of environmentally friendly composites, in which significant amounts of chemically modified or unmodified hemp fibers were used, with or without the addition of a small amount of glass fibers on a polypropylene matrix.The possibility of using various types of composite structures decommissioned for energy purposes in the future, e.g., elements of car bodies and linings, elements of wind power plants and elements of hulls or superstructures of vessels, which will be made of a composite reinforced with industrial hemp fibers (HFRP), will recover a significant amount of energy (ca.98% of the structure weight) and additionally ash obtained in the combustion process (ca.2% of the weight of the structure), which can be used as a component of effective natural fertilizers.
This class of new products can be extensively used in a wide range of economy sectors, including automotive, construction, energy, and ship-building industries.

Highlights
• Conducting a comparative analysis of chemical compositions of selected plant natural fibers (NPF).• Conducting a comparative analysis of the physical and mechanical properties of NPF in relation to commonly used synthetic fibers (SF).• Determination of tonnage resources of world NPF production according to their types.
• The origin and importance of industrial hemp and its impact on the development of civilization.
• The current state of legal conditions for the cultivation and processing of industrial hemp in Poland and in the world.

1. 2 Figure 1 .
Figure 1.Examples of fibrous plants abundant in different regions of the world.
Figure 3. Hemp on the Tibetan plateau near Qinghai Lake (3196 m), cannabis varieties, and leaf size of Cannabis varieties.

Figure 4 .
Figure 4. Historical map of the spread of industrial hemp/cannabis in the world (Warf 2014).

Table 2 .
Properties of several natural (plant) fibers and commonly used synthetic (mineral and carbon) fibers.

Table 4 .
Comparative analysis of the characteristics of mineral (glass) fibers and natural (plant) fibers.