The generation of over 150 million tons of hemp waste annually is as much of a sustainability challenge as it is an opportunity for the circular bioeconomy. This review provides a critical analysis of the recent trends in the use of industrial hemp waste as a precursor to producing sustainable bioproducts. The objective is to synthesize the current state of knowledge and to identify the various pathways for valorizing hemp waste beyond the traditional applications. The methodology involved the systematic assessment of the recent literature to identify the applications in textiles, biocomposites, packaging, and, most importantly, advanced areas such as hemp-based carbon materials for storing energy, biomedical materials, and smart biomaterials. Findings showed that hemp waste is a versatile material for creating high-value products, as it shows promise in carbon electrodes for supercapacitors as well as reinforcement for 3D-printed biocomposites. However, there are some limitations in terms of standardization and scalability. The review concludes that future progress depends on multidisciplinary research to optimize conversion and utilization processes, including the development of comprehensive life-cycle assessments and reliable supply chains.

This study investigates the use of carbonized hemp fiber (CHF) as a reinforcement for phenol resorcinol formaldehyde (PRF)-based fiber composites. The hemp fiber was carbonized slowly up to 1000 °C under N₂ with a yield of 18%. Compression-molded composites were prepared with CHF and then compared to hemp (HF) and wood fiber (WF) at 0 to 50% loading with PRF resin. The flow characteristics of the uncured composites were determined by dynamic rheology and showed pseudoplastic behavior; the composites show promise as extrudable materials. The flexural strength of the HF composites (69 MPa for 40% HF) was higher than the CHF composites. The thermal stability of the composites was determined by thermogravimetric analysis (TGA), and the CHF composites were more stable than the HF and WF composites. Carbonization was shown to enhance both the thermal stability and the hydrophobicity of the composites, which is expected to lead to less susceptibility to weathering and biological attack. Formulations of 50% WF, 50% CHF, and 30% HF fiber loadings with PRF were able to be extruded into rods. Extruded CHF composites showed better mechanical properties than the HF and WF composites.

Biobased composites from fast growing hemp have drawn significant attention because they are inexpensive, biodegradable, sustainable, promote the circular economy, and have good mechanical properties. This proof-of concept study focused on utilizing low value hemp hurd (H), a byproduct of hemp fiber production, as a reinforcement for use in biocomposite materials. The H was characterized by particle size, surface area and chemical composition. Mixtures of 30–50% H and 70–50% phenol-resorcinol-formaldehyde (PRF) resin were blended and subsequently extruded on a single screw extruder. The uncured (wet) blends were evaluated for their rheological properties and showed pseudoplastic behavior. The extruded biocomposites were cured and their water absorption, flexural strength/modulus, and thermal properties were determined. The water absorption properties increased with H content 17% after 12 days for 30 H to 44% for 50 H. The biocomposites containing 40% H had a flexural strength of 41 MPa, while lower values were obtained at 50% and 30% H. These results show that underutilized H can be valorized in extrudable biocomposites.

This original study investigated the effect of biochar (BC) addition, a hydrophobic reinforcing agent, to a thermosetting wood–sodium silicate (W-SS) composite prepared by extrusion for use in additive manufacturing. Commercial BC was blended (10–20% w/w) with W-SS while lowering the SS resin content to form composites. In addition, 50–70% w/w BC-SS composites were also prepared. The flow behavior of the uncured composites was determined by rheometry. The composite mixtures were extruded and cured, and then tested for their flexural, water soak, and thermal properties. Replacing SS content with 10% BC significantly improved the mechanical properties of W-SS while potentially reducing cost and biodegradability; however, 20% w/w BC replacement led to reduced strength. Incorporating BC improved the thermal and dimensional stability of W-SS composites. BC-SS showed improved thermal, hydrophobicity, and flow properties compared to W-SS composites, but lower mechanical properties. It was found that the composite containing 50% W, 10% BC, and 40% SS had an optimum flexural strength of 29 MPa, with thermal property values improving by 29 °C and the dimensional stability improving by 10% compared to 50% W-50% SS (w/w). This implies that BC could help improve the hydrophobicity properties of W-SS while also enhancing mechanical properties, biodegradability, and reducing SS content. 3D printing of the 50% BC-50% SS was demonstrated to showcase the industrial feasibility of printing BC-SS composites. This study demonstrates that BC is an effective additive for enhancing the properties of W-SS composites.