The outcomes of the preliminary specimens are presented in Table 2. However, it should be noted that certain samples became unstable and broke on handling before testing, leading to values in the table without a coefficient of variation. Of particular significance is the case of starch resin, where all the samples prepared proved to be unstable due to the high moisture content of the resin, causing the samples to swell during the curing process, so it was removed from the table.

The primary objective of the initial results was to establish the appropriate blending protocol and validate the specimen fabrication. For non-vegetable resins, an increase in resin quantity corresponds to improved tensile and bending properties. For the white glue, the 2–10 composition (LW-2-I) exhibited a low binder content, producing a good mix.

However, this pattern did not hold true for the vegetable resins. In the case of the 6–10 composition with arabic gum and colophony (LA-6-I & LC-6-I), the tensile samples were unstable. This discrepancy was attributed to residual moisture in these resins, which led to an enlargement of hemp shiv and an expansion of the specimen dimensions during air curing.

Both the vegetable and synthetic resin results obtained fell significantly below the benchmarks set by commercial materials (tensile strength: 0.4 MPa & bending strength: 11 MPa [37]), underscoring the need for production enhancements. Subsequently, the focus shifted toward refining the conducted processes to minimize specimen numbers. These interim steps exclusively involved vegetable resins. Once the final process had been selected, specimens of all types could be produced to facilitate comparative analysis.

Based on the outcomes presented, modifications in the manufacture process were proposed to improve the quality of the samples. In terms of composition, the mechanical strength increased with the amount of applied resin. In the following samples, the compositions were reduced to 10-2/6.

The first suggestion was to concentrate the resins, for the purpose of minimizing moisture within the mold. Initially, the ratio was 2 g of water per 1 g of arabic gum; however, in these instances, a 3:2 ratio was adopted. This proportion was applied to two different cases, 2–10 and 6–10 (HA-2-I & HA-6-I). In both cases, the dimension expansion of the specimens decreased during curing. This effect was more pronounced in the 6–10 case, where a greater reduction in water was achieved, resulting in improved stability.

By using concentrated resin with a lower amount of water, the arabic gum also achieved better mechanical resistance with a higher amount of resin, Table 3. Conversely, in cases of lower resin content, the diminished water usage (and subsequently lower reduction in overall water quantity), as well as the challenge in blending the two components with a smaller amount, produced a reduction in the mechanical properties compared to the non-concentrate case. Based on these findings, it was decided to utilize concentrated resin exclusively in the scenario of the 6–10 composition. This adaptation resulted in a reduction of 30 g of water within the bending specimens.

A further recommendation was to prolong the duration of pressure application within the steel mold for 5 h at 5 MPa, which was then left to air dry for 1 week (LA-2-P). This approach aimed to mitigate sample expansion by allowing more time for resin curing, resulting in higher strength upon specimen demolding. Another approach consisted of 5 min pressure application in the steel mold and then the mold was introduced into a 120 °C oven for 1 h (HA-6-O). Similarly to the previous modification, this method aimed to expedite sample drying, thereby reducing the curing time that the specimen remained in the mold. Samples were also fabricated using smaller-sized hemp shivs (HA-6-T). To obtain finer hemp shivs, the sample was filtered through a sieve, resulting in a median particle size of 5 mm compared to the initial 10 mm medium length. Table 4 shows the results of the different fabrication methods proposed.

Unfortunately, the achieved outcomes were not favorable, mainly because the 5 h duration within the mold proved inadequate for the complete resin curing process. After removing the specimen from the mold, it was observed that the humidity inside the mold was substantial. Moreover, during the week of curing outside the mold at ambient conditions, the dimensions increased significantly. This phenomenon occurred because the binder began to cure inside the mold, causing the hemp to absorb the remaining water, as the mold did not allow moisture to escape. The modification aiming to improve the curing process through elevated temperatures failed to enhance specimen outcomes, as this approach led to the development of internal cracks caused by the swift removal of water. The filtration of hemp shiv in order to use smaller particles did not contribute to improved results. Using smaller hemp particles can enhance the mechanical properties in this composite material [38]; however, the hemp shiv used was already within the described small particle range. In that case, further reducing the particle length produced a reduction in the maximum strength of the sample. Consequently, these attempted modifications were disregarded. The hemp shivs were soaked for 24 h to prevent further moisture absorption from the binder and to prevent volume changes. Nevertheless, utilizing damp hemp shivs hindered the effective curing of the arabic gum, leading to instability of the specimens.

Based on these results, it was proposed to keep a sample in the mold for 1 week applying pressure in order to maintain the shape (HA-6-W), and to use bleeding paper and absorbent paper similar to those used in composite material fabrication with infusion methods, to reduce the quantity of water that was absorbed by the hemp shiv, Figure 4. The wood mold and absorbent paper reduced the moisture absorbed by the hemp, and since the specimen remained in the mold during curing, it maintained its dimensions. With these two processes, the dimensions improved from 15 mm to 10–11 mm, increasing the compactness of the samples, resulting in improved properties, as shown in Table 5. These processes were extrapolated to the other initially considered resins.

Furthermore, for the arabic gum and colophony composites, a two-step curing process was proposed using the wooden mold. This was because colophony, which utilized acetone, did not exhibit as many moisture-related issues. However, it is important to note that the optimal curing time varied for each resin, due to their distinct curing mechanisms, as indicated in Table 5. For arabic gum, water absorption by the wood and paper components creates a high-moisture environment over an extended period, which can decrease the strength of arabic gum, and the hemp shiv may also absorb moisture, reducing its mechanical properties. In contrast, colophony undergoes elimination upon contact with air. In the mold, the evaporation process is slower, resulting in a more resilient sample with one week of curing time. In this scenario, the most favorable outcomes were achieved, with values approaching those of commercial materials (tensile strength: 0.4 MPa & bending strength: 11 MPa [37]). Consequently, this modification was implemented for the other binders as well.

In the initial stages, corn starch was utilized as a binding agent. However, the material exhibited instability due to the significant amount of water required for the binder. Through refining the manufacturing process, which involved employing a wooden mold with a drainage system and allowing for one week of drying time with absorbent paper, the mixture became sufficiently stable for mechanical testing (LS-0.5-D & LS-1-D). The results obtained from using food-grade starch, coupled with this optimized manufacturing approach, are detailed in Table 5. Nevertheless, these outcomes fell short of those achieved with the two vegetable resins applied. In the case of 1–10, the samples remained unstable due to the high water content in the mixture, even with the improved fabrication method.

In Table 6 and Figure 5, a comparison is presented between all the resins employed in the study and the top-performing scenarios. The fabrication process involved applying pressure for 5 min, followed by placing the sample in a wooden mold with absorbent paper for curing. For white glue, bioepoxy, and colophony, the curing period was 1 week, while for arabic gum and corn starch, it was 1 day. For the case of colophony and arabic gum, the concentrated resin was used. Analyzing these findings reveals that, when compared to commercial benchmarks, the attained tensile strength improved the best instances by a factor of up to 5. Nonetheless, the bending strength remained within the range of 50% of that seen in commercial boards (tensile strength: 0.4 MPa & bending strength: 11 MPa [37]) for the most successful cases, arabic gum 6–10 (HA-6-D). The medium density of the samples manufactured was 480–500 kg/m³, obtaining a lower density comparing to commercial chipboard, 550–800 kg/m³. The difference in density and the volume expansion presented in the sample indicated that the curing process can still be improved to obtain samples with better mechanical performance. Regarding the attained outcomes, the current material’s suitability as a particle board is limited due to its lower bending mechanical characteristics. Considering the best case scenario with arabic gum, the bending Young’s modulus was 50% lower than commercial materials (1800 MPa [37]). Additionally, the amount of binder used was higher, with a 5–10% ratio in commercial chipboards [37].

Nevertheless, with this mechanical performance, this green composite material could be used in some applications in the construction sector. The coffered ceiling is a suitable application, because its mechanical properties are suitable, with a similar density to commercial materials and moreover it also has insulating properties that could be interesting for these applications. The attained mechanical strength values met regulatory standards, and its bending strength was two times greater than EPS (150 Kpa) in the case of 2–10 with colophony (350 kPa). Colophony was chosen for its hydrophobic properties; moreover, colophony protects the cellulose, hemicellulose, and lignin from alkaline environments [39,40]. Therefore, it shields the hemp shiv from the alkaline environment created by concrete. It is necessary to protect the material during the initial week to prevent degradation of its mechanical properties. In the case of arabic gum, since it is soluble in water, the material may not be resistant enough to withstand the weight of the concrete until it is fully cured. Nevertheless, it is crucial to acknowledge that an excessively alkaline environment could also break down the vegetable binder, hinder its advantages, and produce an unstable material.

After the concrete is poured and undergoes curing, these blocks become an integral component of the structure. It is crucial to verify material compatibility and ensure that the green material remains stable for at least 7 days, allowing the concrete curing process to take place without degradation of the mechanical properties of the bio-composite or the concrete.

Table 7 presents a comparison of the compression Young’s modulus and bending strength of the hemp-based materials. The mechanical properties of the composite were significantly influenced by the binder used. It is interesting to note that introducing vegetable materials into a matrix like cement significantly reduces the mechanical properties of the material, even to the point of making it inefficient for use as a structural material. In such cases, using a material that is 100% vegetable for non-structural applications increases the options for introducing more eco-friendly materials into the construction industry.

The material developed in this study showed a good performance for non-structural applications in constructions compared to other green materials. It could be use in some applications replacing materials like chipboard or wood-based materials with similar mechanical performance or EPS. Increasing the use of renewable materials in the construction sector with these materials.