Evaluation of the Hemp Shive (Cannabis sativa L.) Energy Requirements Associated with the Biocomposite Compaction Process

Abstract

The main purpose of the present study was to develop an environmentally friendly and economical biocomposite that can be used to make hemp shive (Cannabis sativa L.) chipboard. The study involved the creation of a sample made of hemp shives and PLA (Polylactide) thermoplastic with varying amounts of concentrations of this plastic (25 and 50%) following a series of testing studies. The variabilities were differentiated fractions at four different levels (f₁, f₂, f₃, and f₄) ranging from 0–2 mm, 2–4 mm, 4–6 mm, and 6–8 mm. In this light, the purpose of this research was to optimize the parameters that will affect the compaction process and strength of the biocomposites the researchers tested, which were made from shredded hemp residues and PLA (polylactide). According to this hypothesis, the quality of the biocomposite produced depends on the variation of fractions that constitute the composite. This study aims to provide insight into the energy requirements associated with the production of a biocomposite from hemp scraps and PLA thermoplastic, in order to determine its feasibility. The study compared the densities of different hemp fraction mixtures. The conversion factor (χ) was used while calculating the specific density of the fractions, f₁, f₂, f₃, and f₄, which came to 1377.33 kg·m⁻³, 1122.27 kg·m⁻³, 1071.26 kg·m⁻³, and 1275.31 kg·m⁻³, respectively. The specific density of blends containing 50% PLA material was calculated to be 1326.32 kg·m⁻³. For blends containing 50% PLA, by taking into account the conversion factor, the density fractions were 1324.29 kg·m⁻³, 1428.34 kg·m⁻³, and 1479.36 kg·m⁻³. Using different types of mixtures and fractions to analyze the total compaction work values: Based on the addition of 50% PLA to fractions f₃ (4 ÷ 6) and f₄ (6 ÷ 8), bulk density ranged between 221.09 kg·m⁻³ and 305.31 kg·m⁻³. Based on the compaction process results, the density values for the various fractions ranged from 1101.28 kg·m⁻³ to 1292.40 kg·m⁻³. Depending on what density is desired, the amount of compaction work required, on average, ranges from 1.1 × 10⁻⁵ J to 4.5 × 10⁻⁵ J.

1. Introduction

In recent years, there has been growing interest in alternative energy sources that are environmentally friendly. Traditional energy sources have contributed to environmental pollution growth and the need to reduce greenhouse gas emissions. The use of plant biomass as a raw material for semi-finished products is one of the promising solutions in biotechnology. Researchers are increasingly recognizing the importance of sustainable products and intermediates in developing sustainable products. The hemp plant (Cannabis sativa L.) is a plant with many benefits, including fast growth, low fertilizer requirements and pesticide needs, and the capacity to grow on a variety of soils and thrive in all weather conditions. Hemp fiber makes for an attractive raw material for biocomposites because it also has a high fiber content. There are a number of potential applications for hemp biocomposites that will make them a viable replacement for materials like chipboard, for example. This can be achieved by introducing a range of enhanced properties. Hemp is a plant that is gaining popularity in various fields. One of hemp’s potential uses is the production of briquettes and pellets from its residues.

The use of hemp as a fibrous material goes back thousands of years, and much research has been conducted on the topic and many scientific papers have been published on it. The uses and manufacturing processes of hemp can be found in several books, both as a fiber and as a raw material for paper, plastics, and other products [1,2]. The research description of hemp concentrates on not only its industrial use, but also the aspects of its use in construction activities, such as hemp concrete, and the characteristics of the material [3]. Additionally, Ernest Small and David Marcus recognized hemp’s potential in the book, Hemp: A New Crop with New Uses for North America [4]. They published a scientific paper that analyzed various aspects of hemp cultivation and use, including the fibers of hemp, to determine the potential of hemp as an industrial crop. A research report conducted by the WSU Center for Sustaining Agriculture and Natural Resources, Industrial Hemp, Opportunities and Challenges for Washington’s Hemp Industry [5], describes the opportunities and challenges that are associated with the use of industrial hemp.

The literature above merely comprises an overview of a wide range of topics that are related to the use of hemp as a fibrous material, and it does not encompass all the topics. There are many advantages to using stem fibers [6,7], as they are strong, durable, and rich in cellulose. This makes them ideal to be used for making construction materials and reinforcement materials, owing to their strength and durability [8,9]. The hemp stalk, or straw, has a core that is usually chopped into small pieces called shives. These shives are usually made from this core. Hemp straw can be mechanically processed (hulled) to obtain approximately 35% fiber and approximately 65% of shives [10]. The amount of shredded material you can obtain from a hemp-straw-harvesting operation with a capacity of about eight tons per hectare is about five tons of processed material. Hemp cultivation, with the right agricultural technology, yields high yields of biomass that amount to about 10–15 tons per hectare. This results in high profits if the crop is maintained uniformly and grown with the right agricultural technology. A mature hemp plant can reach a height of 2.5 m or even 3.0 m [11].

There has been growing interest in using hemp in a utilitarian manner in the last few years, particularly in the market for cannabis products that are certified [4,12]. There are many products that can be made from hemp, which can be used in the production of a wide range of products, as well as being used as filler in particleboard. A new approach to agricultural waste management can be achieved through the compacting of shredded material, yielding products with new properties, and reducing the amount of agricultural waste. There is a lack of understanding about the entire process, and one of the key parameters is the moisture content and dimensions of the raw material fraction, which is one of the most important considerations [7]. The biomass obtained from hemp shows a high level of efficiency as a raw material, and there is a growth of approximately 50 cm in the stem of the plant in only one month [13]. The shives that are produced when hemp straw is processed, and which are a part of hemp that is particularly profitable in terms of energy, are a particularly valuable part of hemp.

The idea of creating a new product involves combining hemp with a thermoplastic that has biodegradable properties, in order to create a new product. There are a number of different fields in which polylactide (PLA) is used and it plays an important role in a variety of industries. Various sources of thermoplastic can be used in the production of thermoplastics derived from lactic acid, including starch, cane sugar, glucose, cornmeal, and starch polymerized into lactic acid. It is most commonly used to make raw materials from corn since this raw material is readily available in a wide range of locations. In the case of PLA (Polylactide), the material is biodegradable, which means that when the microorganisms present in the environment disintegrate it, the material disintegrates. This is a very important aspect of technology that contributes to reducing the industrial process’s negative impact on the environment as a whole. Because lactic acid is produced from plant-based raw materials, polylactide is also renewable since it is made of lactic acid. It also has good mechanical strength as well as stiffness, which can be attributed to this material. The mechanical properties of this material, its biocompatibility, and its environmental friendliness make it a desirable material for a variety of applications.

The advancement of biocomposites will lead to new opportunities for commercial and ecological growth. The possibility of creating biocomposites using hemp is also an interesting research area, due to the fact that the material has the potential to be a replacement for standard plastic- or fiberglass-based composites. To produce composites via hot pressing, hemp fibers are mixed with a polymer matrix, such as polypropylene, and pressed at a temperature above its melting point at a high pressure. The result is biocomposites that are durable and rigid. Injection molding, which is one of the most popular processes in the industry, is another popular method. Polymers can be dissolved in a liquid state and injected into molds to manufacture hemp fibers. The process of cooling the plastic leads to the production of a composite with the mechanical properties and shape you want. Composite materials can be cast (casting), which involves mixing hemp fibers with a polymer matrix and pouring them into a mold. Using nonwoven techniques, composite materials can also be produced using this technique by impregnating the fibers with polymer during production. In the automotive and construction industries, among others, lightweight and strong materials are made as a result of this process. The production of composites made from hemp nanoparticles is a modern, quite innovative method of manufacturing composite materials. Researchers have been experimenting with hemp nanoparticles to strengthen composite materials and improve their mechanical properties while introducing 3D printing. The manufacturing method should be chosen based on the application and product requirements. In general, the best method depends on the specific requirements of the project and the availability of raw materials.

2. Materials and Methods

2.1. Tested Material

In the creation of the biocomposite, hemp shives were used as the main sub-product, which served as the compound’s basis of development. The species, Cannabis sativa L., is classified into two types of hemp, fiber hemp (Cannabis sativa L. var. sativa) and indica hemp (Cannabis sativa L. var. indica), which differ in their concentration of cannabinoids [13]. The fibers of hemp are classified as stem bast fibers [7]. In comparison to other energy crops, hemp gives lower yields than certain other plants [14]. It has been found that hemp is a biofuel feedstock that is highly calorific and has a low ash content, which is why it is a popular feedstock for biofuel production as well [15]. Hemp fiber is capable of containing a value of over 18 J/kg of energy, while wood only has a value of 17 J/kg of energy [16,17,18]. It has been reported that during the combustion process of hemp biomass, the emission values are approximately 0.8 kg CO₂/kg and do not exceed 0.1 kg CO/kg by weight of raw material as far as CO is concerned [19].

A lignocellulosic material such as hemp shives has a light texture and can be composed of lignocellulosic molecules. This makes it an ideal material for a variety of industrial applications, including insulation, biofuel production, and animal bedding. It is also suitable for use in composite materials such as panels and boards. However, the density of hemp shives can vary due to a variety of factors. A number of factors can influence the growth of hemp, including the variety of hemp, climatic conditions, soil, fertilization, and cultivation practices. When the hemp seeds are harvested from the hemp plant, the twigs and shives become soft and fibrous, forming what is called the hemp shive or hemp twig. In terms of density, shives have a direct correlation with their volume of coverage and their weight per specific unit of volume. Hemp shives can be used for insulation, bedding, straw, and other materials. They are also used to create biodegradable plastic, paper, and fabrics. Hemp shives also contain a high level of cellulose, which is a major component in the production of biofuel. The sample of prepared raw material and PLA share for biocomposite was presented in Figure 1.

The study was conducted with the use of a thermoplastic Polylaktyd (PLA) binder, combined with hemp shives (Cannabis sativa L.). The composite material was made by combining hemp shives together with a thermoplastic polymer to form a composite material [20,21]. This study selected poly(lactide acid) (PLA) as the thermoplastic for the preparation of the biocomponents to be used in the study. The majority of renewable thermoplastics are made from plant-based materials such as corn and potatoes, which makes them a more environmentally friendly option [22]. A major benefit of the material is that it is highly elastic and plastic, and the elasticity increases with an increase in melt flow. Temperatures between 190 °C and 230 °C are considered suitable for this process. Material forms are advantageous because of the fact that they are environmentally friendly as a result of their forming process [23]. Throughout the study, it can be found that composite materials made from polylactic acid (PLA) have significant potential to replace traditional synthetic materials that cannot decompose or be recycled.

The use of PLA (polylactic acid) thermoplastics instead of traditional synthetic materials has many environmental and social benefits. In contrast to plastic, PLA material is biodegradable, meaning that it can decompose naturally without creating a permanent environmental impact. The reason is that PLA can be produced from renewable sources like cornstarch or sugar cane, thereby reducing greenhouse gas emissions. There is potential for this material to be popularized in order to reduce the use of plastics, which are a troublesome source of pollution. The benefits of replacing traditional synthetic materials include improving air and water quality, reducing landfill waste, reducing impact on marine ecosystems, and encouraging conscious and sustainable lifestyles. Sustainability and greener living can be achieved by replacing traditional synthetic materials. Developing sustainable products through PLA-based biocomposites is an excellent means of achieving this [24].

2.2. Dividing the Material into Fractions

Hemp, like every semi-finished product, should be properly prepared for further processing. In order to conduct the study, hemp raw materials, as well as PLA, were pre-treated before use. At the beginning of the controlled compaction process [25], hemp shredding is the primary step. Hemp seeds were shredded in a laboratory with a shredder [26]. This study used a sample that was shredded to less than 8 mm in thickness. The literature review established that hemp material with a fraction length in the range of 0 to 8 mm is the most suitable for biocomposite production of the assumed shape and size [6]. By measuring the length of a fragmented piece of material, the length of the fragment can be studied further to provide further information about the fragment. The assumed size of the biocomposite with a diameter of up to 14 mm was achieved with the specially prepared cylindrical compacting tube with a head. There was a point in the process where the diameter of the shredded material had to be considered. The material that has been tested needs to be separated after it has been processed through the shredding process.

In this case, the raw material is separated followed by fractionation using a sorting machine [27]. For this purpose, an orbital shaker from C.B.K.O Hydrolab was used to achieve the desired effect [28]. In accordance with [29] PN-EN 15149-1:2011 and [30] PN-EN 15149-2:2011, the material was divided into fractions through a sieve separator in accordance with Polish norm. In accordance with the sieve mesh size, the material was separated into four fractions. It turned out that based on the results obtained from the study, we could identify four groups of fractions. It was separated into mineral f₁(0 ÷ 2), fine f₂(2 ÷ 4), medium f₃(4 ÷ 6), and thick f₄(6 ÷ 8). There was a similar process of shredding the hemp material and the PLA material, both in a similar manner, following the same procedure. The fragmented material was mixed according to its weight after fragmentation. In order to prepare a base for further research, mixtures of 25% and 50% PLA with hemp shavings were created. According to the purpose of the work and the preparation of the materials, the mixture was prepared.

The process of measuring the material’s moisture content is one of the critical steps in ensuring that the compaction process is conducted under the correct conditions [19]. This study also took into account the sample hygroscopicity parameter by measuring moisture content in the sample in order to assess sample hygroscopicity. In accordance with the guidelines, the material should be maintained at a constant moisture level throughout the entire process [31]. It was decided to test the moisture content of shredded prepared mixture samples. There are a number of suggestions in the literature indicating that the recommended moisture content for raw material used in compacted biocomposites should be between 12% and 15% [19]. The procedure for determining the moisture content of samples was to dry the samples in a laboratory chamber at 105 °C until they were absolutely dry. It was then necessary to weigh each sample after the drying process had been completed [32]. The samples were weighed and then placed into a laboratory cuvette to standardize the moisture content after they were taken out of the dryer and weighed [33,34,35]. The moisture content of the sample after a period of one week was recorded to be 12%. It is very important to control the moisture content of the prepared material before it is compacted in order to ensure that it is as dry as possible. In order to perform the weighting test, a Radwag WS30 weighing dryer has been used as a tool during the course of the testing process.

2.3. Determination of Bulk Density

The bulk density of a material is characterized as a material parameter, which determines how much mass of that material is contained within a specific volume. The bulk density, or amount of matter a space contains, can be measured in terms of how much mass the space holds. The calculation of the ratio of the tested mass substance to the volume was carried out by measuring and analyzing the bulk density. The volume that the material occupied, the space between the particles of the solid, and the air during the calculation were considered as well. In the measurement process, the filling factor was taken into account in addition to the actual volume of the raw material. For the purpose of measuring bulk density, the empty, dust-free, and dry container used for this purpose needs to be weighed. There was an accuracy of +10 g in the specimen weighing. In order to fill up the container, excess shredded hemp shives were first placed into the container. This formed a cone 200–300 mm high above the container’s top edge. Using a clean surface, the container with the filled sample was dropped three times horizontally from a height of 150 mm onto a surface that was clean. This process resulted in gaps in the sample, which were filled with raw material or leveled with a strip so that they reached the top edge of the vessel where they were leveled. The containers containing the admixed sample were then weighed again after the admixed sample had been added. In order to measure the bulk density according to PN-EN 15103:2010E [36], a particular container with a specific shape and volume was used.

2.4. Determination of Volumetric Density

Density is one of the most fundamental characteristics of any substance. It can vary considerably depending on the type of material it is made of. The volumetric density of a substance is a measurement of how much mass is contained per unit volume. One of the goals of this study was to determine the amount of matter contained within a container of a particular composition. The method used for this was to use distilled water for the process. The purpose of this calculation was to determine the volumetric density of the container. Using the assumptions mentioned above, it can be concluded that the maximum density of porous raw materials can be determined by the comparison of their full mass (m) to their volume (V), thereby indicating their maximum density. The mentioned volume is a result of the difference between the pure volume of the measuring container [V_pp] and the volume of water [V_wz] introduced to this container until it achieves a marked level. In physical analysis, weighted density is a crucial concept that helps distinguish different substances. It also helps to solve problems pertaining to the mass, volume, and behavior under different conditions of a particular material under study. The bulk density (ρ_o) of the bulk material considered in this study was calculated by dividing the mass of the substance under analysis by the volume it occupies, based on Equation (1).

$${\rho }_o=\frac{m}{V_{\mathrm{pp}}-V_{\mathrm{wz}}} \left[\mathrm{kg}\cdot {\mathrm{cm}}^{-3}\right]$$

(1)

In order to measure the volumetric density of bulk raw material, a specially adapted container was used during the laboratory test. The container was equipped with an airtight lid with a vent and a filler to keep the contents airtight. The vessel could also be used for measuring the external porosity of raw materials with a known mass ratio. This would allow us to determine the type of porosity of the material that makes up the vessel. To perform this measurement, distilled water was saturated into the loosely placed raw material inside the chamber, so that both the external pores and the air gaps in the material were filled with water and both were saturated with water. In accordance with PN-EN 15103:2010E, the capacity of the empty vessel was calculated according to the requirements of the Standard. A measuring vessel was filled with the material that would be tested so that the measurements could be carried out, as required by the same standard, in order to carry out the test. It was gradually added to the vessel using an infusion method until the vessel was completely filled with distilled water at 4 °C. It should be noted that during the testing process, no allowance was made for possible measurement errors arising from swelling or shrinkage of the material, as indicated in [37], which indicates that such errors are in the range of 0.7%. In accordance with PN-EN 15103:2010E, the average density value for the material was rounded to 10 kg·m⁻³ with an error margin of 0.1 kg·m⁻³ (1%), which means that any potential measurement errors taken into account. The measurements carried out during the research were not intended to reflect the precise values for determining the specific density of the raw material, but only the specific density of the material, taking into account the reduction caused by its internal porosity.

2.5. Construction and Functioning of the Compaction Head

For the implementation of the planned research on hemp biocomposite compaction, it was necessary to construct a dedicated test stand for the research. In order to perform the planned strength tests, it was necessary to prepare a suitable test stand in advance. The construction of the stand included a testing machine, a special compaction head, and auxiliary equipment such as a heating module with a control panel. As a result of this, the tests were conducted on it. The compaction head cooperated with the Instron testing machine as a part of the study in order to carry out the experiment. An amount of force of 100 kN was generated by the testing machine. In the compaction head, the piston diameter and chamber diameter were selected in such a way that a unit pressure of 3.5 MPa could be applied to the piston. Based on [38], it seems that the force value, in this case, is enough to bind the shred material to the compaction product. The compaction set was presented in Figure 2.

There were three structural components that were included in the prototype compaction head. The main component of the system is a cylindrical sleeve (labeled No. 1 in Figure 2) which comes on a steel support (labeled No. 2) and connects the system to the testing machine by means of a steel shaft. In the tracing process, there was an active compaction part, namely the compaction head (marked as No. 3) attached to the compaction head, which is the part that was responsible for compaction. Compression heads were designed to achieve a defined unit pressure. The value of the maximum force generated by the testing machine (F_max) and the size of the inner diameter of the compaction chamber had to be adjusted in order to achieve this value. It was determined that the inner diameter of the chamber was equal to 11 mm, based on the calculations performed. The compaction set cylinder height was 100 mm.

The literature suggests that the effective densification of lignocellulosic materials happens at elevated temperatures due to the presence of a thermo-sensitizing agent. The actual compacting process is also accompanied by the generation of internal heat linked to friction as part of the actual compacting process under stable conditions. A laboratory head is a device that is typically used in laboratories for testing purposes; as such, additional heating devices are necessary to ensure that the desired temperature is maintained. In light of this, the laboratory tests used a compaction head equipped with an external heating unit in order to simulate laboratory conditions. To heat the unit, banded heaters (GOGO-04349) were installed. As a result, the temperature could be achieved with an accuracy of 1 °C and could range between 0 °C and 800 °C. A band heater with a height of 25 mm was used. An ESM-3710 controller with 280 W of power is mounted inside the band heater, which allows the process temperature to be controlled with the help of a thermocouple mounted inside the band heater. It was possible to obtain 1% accuracy from the controller’s digital readings.

This study involved the implementation of a compaction head model that worked with a stress-testing machine. This was to perform controlled compaction processes in the laboratory with the help of the compaction head. As part of the process, there were a number of stages, and the parameters of the material (soil moisture content and granulometric composition) and the process (temperature) had to be taken into account. In the first stage of the test, the compaction head was heated to a specified temperature, and then the test was conducted. The second stage of the process involved the introduction of crushed raw material into the chamber of the compaction head. In the third stage of the thickening process, the piston of the thickening head is locked in place within the upper grip of the testing machine. The raw material is gradually thickened as it is introduced. It was then necessary to move the plunger back to its base position in order to remove the product after the compaction process was completed. In order to remove the product, a compression head piston or an additional tool was used, depending on the product. Measurement and control of compaction process parameters were possible due to the design of the test stand. Testing was carried out using a compaction head that had parameters that were compatible with those found on professional machines. Taking this into account, it was concluded that the compaction head reproduces well in the typical setting in which lignocellulosic materials are compacted. In the end, the product had a diameter of approximately 14 mm.

3. Results

3.1. Physical Analysis of Tested Material

To create the final product from hemp shives (Cannabis sativa L.), the lignocellulosic material was mixed with PLA to produce the biocomposite. To make sure that the results of this study were representative of the actual patterns, the materials were divided into fractions of 0 mm, 2 mm, 4 mm, 6 mm, and 8 mm, and then each group of materials was mixed with 25 and 50% of PLA. The presence of different phases in the structure of the formed biocomposite necessitated the consideration of both hygroscopicity and anisotropy in the final product, as a result of the presence of different phases. In order to control the hygroscopicity of the intermediates, the moisture content of the mixture was used to measure the hygroscopicity of the mixture. Anisotropy was observed on the stress distribution when the material was clamped in the compaction sleeve (as it was clamped in the compaction sleeve to ensure compaction). By measuring the mass difference between the dry and wet state of the substance used to prepare the samples, the moisture content of the material used to prepare the samples was controlled at the basic stage, in its natural state. The material taken for analysis had a 30% moisture content, which is natural for hemp material [39]. About four hours were needed to complete the drying of the sample to the point where it could be considered complete. The structures of 50% PLA biocomposites, observed under a 0.75 zoom microscope on the side and on the top, are presented in Figure 3.

There was a noticeable difference between the structure of the samples based on the place of observation, as well as the PLA shares (labeled No. 1), in relation to the sample structure. The main component of the biocomposite was chips of hemp shives, labeled as No. 2. In the sample, PLA shares were observed more on the side, rather than on the top, of the sample. The difference in structure between the two places is probably because the environments in both places are different from each other. The higher temperatures at the top of the sample may have caused PLA shares to migrate to the side of the sample. This is further supported by the higher PLA concentrations in the side samples.

3.2. Comparison of the Density of Shredded Logging Residues

The measurement of the specific and volumetric density of the raw material was one of the technical aspects, that gives a view of the tested raw material in the compaction process characterization. The study was conducted using a method for measuring the external porosity of the raw materials according to the method described in PN-EN 15103:2010E for the container used in measuring porosity. The test is carried out by putting the test material in a pot filled with distilled water. Based on the data obtained, a character value is calculated based on the volumetric density of the material minus the surface area of the pores. The study found that water did not fill all the intercellular spaces and thus resulted in a lower density value observed when the material was measured with a helium pycnometer than when it was measured with a water solution. In addition, the use of the presented method and density conversion factor (χ) proposed in the literature [31] can allow a simpler, more efficient, and cheaper way to measure the specific density of bulk materials.

There has already been an attempt to describe a conversion factor for different fractions of lignocellulosic materials, which has been correlated with the specific density measured with a helium pyrometer [31]. Calculation of the conversion factor characterizes the approximate proportion of internal pore volume in the lignocellulosic material, so it is calculated from the value determined after immersion of the raw material in the medium (distilled water). Using the bulk density as a starting point for calculating the specific density, the above procedure gives more accurate results in comparison to this method. It was calculated that the mean value of the specific density conversion factor (χ), for lignocellulosic material with the fractions group of 0 ÷ 8 mm was about 0.62 (0.047). The specific density test carried out using water can be beneficial for obtaining preliminary and indicative information about the density of the material. The results of the density comparison of shredded hemp shives are summarized and presented in

Table 1. The results of the density comparison of shredded hemp shives.

Mixture	Mean Volumetric Density Measured with Water (SD) 1, kg·m−3	Calculated Value with Conversion Factor (χ), kg·m−3 (SD) 1	Mean Density Calculated as Specific Density (Internal and External Pores), kg·m−3
f1 (0 ÷ 2)	994.89 (5.04)	616.83 (35.62)	1377.33
f2 (2 ÷ 4)	810.65 (2.95)	502.61 (60.43)	1122.27
f3 (4 ÷ 6)	773.81 (17.66)	479.76 (132.71)	1071.26
f4 (6 ÷ 8)	921.20 (4.74)	571.14 (121.87)	1275.31
f1 (0 ÷ 2), 50%PLA	958.05 (3.38)	593.99 (23.87)	1326.32
f2 (2 ÷ 4), 50%PLA	884.35 (1.80)	548.30 (36.86)	1224.29
f3 (4 ÷ 6), 50%PLA	1031.74 (11.48)	639.68 (86.26)	1428.34
f4 (6 ÷ 8), 50%PLA	1068.59 (2.61)	662.53 (67.03)	1479.36

¹ SD—standard deviation.

.

Based on the volumetric density of the shredded hemp sieves measured as a raw material, the average density was 930.41 kg·m⁻³, with a standard deviation of about 7.60 kg·m⁻³. In the case of the mixture, the mean volumetric density measured with water reached 985.68 kg·m⁻³, with a mean standard deviation of 4.82 kg·m⁻³. The average calculated value with conversion factor (χ) for the raw material was 542.59 (87.66) kg·m⁻³, and for the mixture, reached 611.13 (53.50) kg·m⁻³. The water did not reach the inner spaces between the biomass particles during the measurement. Therefore, the study was enriched with a conversion rate of the calculated value with the conversion factor χ, which gives the mean density calculated as specific density and corresponds to the filling of internal and external pores with water. In order to explain the apparent difference in the results, it is possible that the different measurements are the result of different arrangements or geometry among the particles being sampled. It was found that fractions with a smaller cross-section fit together better than fractions with larger cross-sections, over the course of the analysis. Based on the findings of the measurements, the parameter mean density was calculated as a specific density, and a statistical method was applied to determine the statistical relationship between the different mixtures based on the analysis of the results. The statistical relationship between the calculated mean specific density mixture is presented in Figure 4.

It has been shown that after the addition of PLA, the density of the mixture increased. The reason for this is that PLA has a much higher density than hemp, which is why it is more stable. The material without pores acquires a magnified appearance and a greater spatial weight when it is exposed to such a high concentration of mixture, as opposed to its previous appearance and magnification. Based on the results of the post hoc statistical analyses carried out, the relationship between homogenous groups was not supported in this case. Upon analyzing the results, it was found that the p-value was equal to 0.14061, indicating that the result was not significant. In the study, the empirical statistic was calculated as F (2, 77) = 2.880. A similar pattern was found in the results of measurements of the specific density of seed hemp fractions for the original composition and for each fraction that had been measured when it had been mixed with PLA as well. The apparent difference between the measurements may have been due to this reason. For the particle measurement to be as accurate as possible, it is possible that air of varying sizes had been present and was responsible for the inaccurate particle measurement. The measurements could have been adversely affected by the presence. The original granulometric composition was 0.64. These results indicate that specific density testing with water can be useful for preliminary or indicative measurements. The defined coefficient makes it possible to correct method errors using distilled water.

3.3. Analysis of the Compressing Process

The compaction of shredded hemp sieves was conducted in two stages. The first stage of the process of biomass compaction was performed according to the selected distribution of fractions f₁(0 ÷ 2), f₂(2 ÷ 4), f₃(4 ÷ 6), and f₄(6 ÷ 8), without the addition of any additives. In the next step, a mixture was prepared in which 50% comprised PLA, and which was then compressed with individual fractions as the prepared batch was introduced into the mixture. The compacting process of the prepared mixture was carried out at an elevated temperature of 230 °C in order to take advantage of the thermal properties of PLA. Thermal treatment was responsible for the plastic reaction of PLA properties. Hemp shives were the base material for this product, which were compressed at a fixed moisture content of 12%. The entered force was measured during the compaction process. The prepared mixture of shredded hemp residue was compacted in special compaction set that was specially designed for the purpose of compacting hemp residues. The pressure during the compaction process is expected to not exceed 3.5 MPa, which is the pressure induced during the compaction of the chipboard. The dependence relation specific to the compaction process of the 40 kN maximum load is presented in Figure 5.

The results reveal that the compaction of hemp shavings at a temperature of 22 °C did not lead to a consistent and uniform product, while some of them dispersed after leaving the chamber after the compaction process. With the above factors being taken into account, a clear conclusion has been established. It was established that further studies of the compaction process should be conducted at 230 °C, the melting temperature of PLA, while maintaining the separation of f₁, f₂, f₃, and f₄ fractions throughout the experiments. The chart illustrates that the smaller fractions can be compacted more easily than larger fractions. It was found that during the compaction processes in every pure fraction, some disturbance appeared. This disturbance could have been caused by the squashing of material particles, but after that distribution, the process returned to normal compaction conditions. It is important to emphasize that at any given moment, the compacting device head moves at a constant speed of v = 5 mm·s⁻¹. Consequently, the changes in the compaction force as a function of the head displacement will be similar in type and magnitude.

It has been observed that in each case, in the initial phase of the experiment, the pressure in each case was close to zero. This signifies the process of kneading the material and removing the air that is between them by pushing it out as they knead. There is a negligible amount of force required during this phase, which has not been determined by the equipment used to conduct the test. The force of the impact was noticeable only when the biomass was crushed, causing it to deform and become more compact. Significant variation was not noticed in the final volume of product that could be produced with and without the effect of temperature on the changes in compaction force. The same applies to biocomposites that have been produced at elevated temperatures. By progressively increasing the temperature and changing the proportion of PLA in the process of densification in accordance with the hypotheses, it was possible to obtain a deeper understanding of the relationship between the studied parameters and the densification process. The dependence relation specific to the compaction process of the biocomposite with 50% PLA for individual fractions is presented in Figure 6.

The compaction process is similar in each of the cases studied based on the analysis of the graphs. It can be seen that the compaction force of the biocomposite with 50% PLA changes over the course of the compaction process for the different fractions of the composite. It was noted that in contrast to the hemp compaction itself, compacting the mixture had an inverse relationship to the fractional share. This was probably due to the fact that the heated thermoplastic bound more easily to the fine size of the raw material and made the piston travel longer. During compaction largest fractions of material, the thermoplastic did not fill all the pores and spaces. There are differences between the phenomena that occur during the aggregation of wood chips of different sizes. Compared to the group of fractions, f₂ and f₄, the fraction from group f₁ has the most open area, so the pressure is increased in a gentle manner; in the fractions, f₂ and f₄, the pressure increases more sharply.

In order to study the impact of fractions further, the gathered results were analyzed using the energetic value of hemp shives (Cannabis sativa L.) in biocomposite compaction. This objective can be achieved by analyzing the total work value of the compaction process in accordance with specific parameters in order to determine its value. Mostly, the third-degree polynomial has been fit into the arithmetic function described above (y = ax³ + bx² + cx + d) to model the compaction process of shredded hemp sieves. The estimated model was based on the Gauss–Newton least squares method results. The coefficient of determination R² was not greater than 0.01, which provided a sufficient level of accuracy in fitting the mathematical model to the analysis. It was noted that when the angle of dilation of a function was large, there was a tendency for the function to take the form of a linear function. Using a second-degree polynomial in this situation would have been sufficient to solve the problem. The integral equation, a summary of the coefficients of the function, and the values of the overall work of compaction with specific parameters, along with a summary of the calculations regarding how to evaluate the coefficients are presented in

Table 2. The integral equation of total compaction work.

Total Work Carried Out under Specified Conditions W(τ, φ)	Determination Coefficient R2	Displacement l, mm	Total Compaction Work, J
$W_{\left(f_1,22 °C\right)}={{\displaystyle \int }}_0^{0.001\cdot l}0.0046x^2+0.1909x$	0.991	10.76	1.1 × 10−5
$W_{\left(f_2,22 °C\right)}={{\displaystyle \int }}_0^{0.001\cdot l}-0.0029x^2+0.2477x$	0.996	12.05	1.4 × 10−5
$W_{\left(f_3,22 °C\right)}={{\displaystyle \int }}_0^{0.001\cdot l}0.0014x^3-0.0341x^2+0.3317x$	0.990	17.73	3.0 × 10−5
$W_{\left(f_4,22 °C\right)}={{\displaystyle \int }}_0^{0.001\cdot l}0.0002x^3-0.0033x^2+0.0937x$	0.996	21.73	4.5 × 10−5
$W_{\left(f_1, 50\%PLA,230 °C\right)}={{\displaystyle \int }}_0^{0.001\cdot l}0.0074x^2+0.0821x$	0.998	13.43	1.7 × 10−5
$W_{\left(f_2, 50\%PLA,230 °C\right)}={{\displaystyle \int }}_0^{0.001\cdot l}0.0024x^3-0.0188x^2+0.1197x$	0.999	11.48	1.3 × 10−5
$W_{\left(f_3, 50\%PLA,230 °C\right)}={{\displaystyle \int }}_0^{0.001\cdot l}0.0014x^3-0.0105x^2+0.096x$	0.999	13.12	1.6 × 10−5
$W_{\left(f_4, 50\%PLA,230 °C\right)}={{\displaystyle \int }}_0^{0.001\cdot l}0.0142x^2+0.066x$	0.990	10.70	1.1 × 10−5

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According to the results of the statistical analysis, the decision to use a third-degree polynomial to describe the forces occurring during the course of the compaction process was a valid choice. There were two instances in which the fit of a function with a tendency to follow a linear trajectory required a polynomial of the second degree. In the case of trend lines, the polynomial showed an R² coefficient equal to or above 0.990. The total work of the material compaction process was calculated using the value of the change in compaction force over time for various raw materials and process parameters. The results showed that the total work of the material compaction process was closely related to the polynomial fitted to the trend line. Therefore, it might be possible to utilize the polynomial to accurately predict how much work will be put into the process as a whole. By calculating the packing factor using distilled water in addition to the density of the material, it is possible to determine how much material has been compressed in relation to the density of the material before deformation. The total compaction work values for all fractions and selected temperatures is presented in

Table 3. Total compaction work values for all fractions and selected temperatures.

Mixture	Mean Volumetric Denisity (SD) 1, kg·m−3	Mean Density Calculated as Specific Density (Internal and External Pores), kg·m−3	Mean Density After Compaction (SD) 1, kg·m−3	Total Compaction Work, J
f1 (0 ÷ 2)	284.26 (1.18)	1377.33	1144.33 (0.84)	1.1 × 10−5
f2 (2 ÷ 4)	231.62 (0.68)	1122.27	1101.28 (1.80)	1.4 × 10−5
f3 (4 ÷ 6)	221.09 (0.93)	1071.26	1292.40 (1.21)	3.0 × 10−5
f4 (6 ÷ 8)	263.20 (0.99)	1275.31	1277.82 (2.52)	4.5 × 10−5
f1 (0 ÷ 2). 50%PLA	273.73 1.90	1326.32	1167.49 (0.42)	1.7 × 10−5
f2 (2 ÷ 4). 50%PLA	252.67 (1.11)	1224.29	1117.94 (0.90)	1.3 × 10−5
f3 (4 ÷ 6). 50%PLA	294.78 (1.52)	1428.34	1187.55 (0.61)	1.6 × 10−5
f4 (6 ÷ 8). 50%PLA	305.31 (1.60)	1479.36	1167.16 (1.26)	1.1 × 10−5

¹ SD—standard deviation.

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The analytical studies were conducted to find the influence of the parameters of selected raw materials on the process of compacting hemp shives. The analysis was carried out using the variance analysis in order to assess both the significance of the differences and the strength of the impact of each of the factors. The post hoc statistical analysis of the factors resulting from the material compaction process did not show that any of the factors were statistically significant. It was determined that separate homogeneous groups cannot be created. The p-value was 0.08157, not enriching the cut-off value of 0.05, which was insufficient to establish separate groups. According to the study, the empirical statistic was calculated as follows: F(1, 6) = 4.3691. During the analysis, the main objective was to determine whether the addition of PLA blends to the biocomposite production process would have an impact on the quality of the product. The statistical relationship between the total compaction work and the mixture type is presented in Figure 7.

It was observed that there is an interesting regularity in the graphs, with increases in fraction size at the end of the process. Because of the longer head movement, there is a greater displacement of the head, with results a lower height compression product, in conjunction with the larger head displacement. It is estimated that during the process of fraction f₁, the head moves for an average of about 10 mm; for fraction f₂, about 12 mm; and for fraction f₄, an average displacement is almost 22 mm. There is a high probability that this phenomenon can be explained by the better initial packing of fine fractions. There is also some significance in the effect of temperature on the aggregation process of the individual fractions. In the case of fraction f₄, the highest aggregation was observed, followed by fractions f₁ and f₃, which could be due to the dissolution of PLA within the pores of the raw material. Any significant difference was not found in the duration of the process running between the densities. Based on the results of this study, it can be concluded that the temperature of the process is not able to completely compact the material. Furthermore, when using the PLA without the use of a compaction head, the material is not sufficiently compressed. This means that when the product is removed from the compaction head, the material expands and spreads even more. Based on the visual observation conducted by the experimenter, it can be concluded that as far as durability is concerned, it would be beneficial to process the PLA at 230 °C with the binder.

4. Discussion

The aim of this study was to optimize the parameters that are responsible for affecting the compaction process of crushed shredded-hemp-based residues. It was found that the test material had an unusual composition, with shredded hemp shives being present in a fairly high concentration. There was a distinct difference between this raw material and the most common manufacturing materials, based on its composition. In accordance with the scientific literature, this research was exploratory, since there was insufficient information available about the physical properties of the material, its susceptibility to compaction, and how its parameters would change over time. In order to compare the results obtained with what is available in the literature, the values obtained were compared.

According to the results of the compaction process, the amount of work performed ranged from 1.1 × 10⁻⁵ J to 4.5 × 10⁻⁵ J for the different fractions. A comparative analysis was performed by relating the values obtained to the unit mass value and comparing the results with those found in the literature [40] for the purpose of a comparative analysis. In terms of specific energy consumption, the average specific energy consumption during the compaction process after conversion is 0.097 MJ·kg⁻¹. In order to compare the results of the compaction of shredded rice straw of fractions of 1.8, 5, 10 and 15 mm, it has been determined that similar material parameters (15% moisture content) should be used for the compaction of this material. It was found in this case that the average specific energy consumption during the compaction production process was 0.098 MJ·kg⁻¹ [40]. According to the literature, it is also reported that the compaction of pine sawdust (with a moisture content of 8 to 20%) is possible at 22 °C, and that the average specific energy consumption for this type of process is 0.027 J·kg⁻¹ on average. This can be seen as an example using poplar sawdust, which has the same moisture content and whose average value is 0.025 MJ·kg⁻¹ [41], whereas birch sawdust has a moisture content of 12% [42].

The composition of the grain in raw materials undergoing compaction plays a significant role in both the compaction process and the charring process as well. According to the results of the study, it was found that the total work energy of the densified raw material increases between 10% and 20% with an increase in moisture content of the raw material (at a constant process temperature). Based on our observations, the moisture content of the raw material needs to be kept within the range of 10–15% to ensure its quality. In their study of raw material moisture content versus chamber diameter, Skonecki and Laskowski [43] also pointed out the existence of similar relationships. The results obtained by Wang et al. [40], who examined shredded straw in their study, however, showed a different outcome. The researchers found that the B-mix, which was more sensitive to variations in temperature and had a higher specific energy consumption at 230 °C (0.165 MJ·kg⁻¹), had a significant difference in energy consumption when compressed, in comparison to the mix, which was more vulnerable to temperature variances. According to Wang et al. (2016), these results differ from those obtained in studies on the compaction of straw mixtures [40]. Considering the results obtained from the experiments, it can be concluded that, in order to reduce the amount of energy consumed during the compaction process, it is recommended that the fraction of the shredded log residue that has a size of 1 to 8 mm be compacted.

5. Conclusions

It has been found that it is necessary to prepare the appropriate measurements as well as methodological tools in order to analyze how material and process parameters affect the processes and the products. The tests were based on standards and measurement procedures that were conducted with standardized equipment. The research could be furthered by using potential binders or additives from other types of biomaterials to continue the work. The same methodology could also be used in order to carry out a second study, with a different type of plantation. The objective of this work was to identify the optimal process parameters and to prepare raw materials in the best way possible for the production of biocomposites. According to the results of the experiments conducted and the statistical analyses conducted, the assumptions of the general influence of the parameters on the outcomes of the experiments were confirmed. It is recommended that shredded hemp shives be compacted at 230 °C in order to minimize the amount of energy consumed during the process. The compaction process, which uses PLA as a binder, facilitates the compaction of the material despite the fact that higher energy consumption is not specified. The experiments that were conducted also revealed that water can be used to measure the volumetric density of hemp shavings, as a result of a simple experiment. There was a lack of consideration in the basic research on hemp shive compaction, due to the innovative nature of the process, for the use of binders other than PLA, which is more biodegradable than other thermoplastics and other binders.

The main purpose of this paper was to discuss the development and composition of biocomposite materials. The possibility of manufacturing chipboard from these materials in real-world conditions is a crucial aspect to address in order to gain a better understanding of how long these materials can last and in order to be able to make efficient and reliable furniture. For example, materials used in long-term applications should be expected to perform well. For the purposes of identifying a solution, a follow-up study should be conducted with the specific objective of evaluating whether chipboard made from PLA or hemp-based biocomposite materials has a longer lifespan and greater durability. In this study, comprehensive testing methodologies have been be applied to assess factors such as durability and strength. Further research on these materials will provide valuable insight into the practical applications that can be made from them and help to address the concerns regarding their long-term viability. Using waste materials such as hemp shives could be an exciting new way to research the use of waste materials in the future. Moreover, further research should be carried out to determine whether the harvesting, transportation, and processing of hemp shives will be economical and efficient in terms of energy and resources.