# Integrating Cork Biochar as a Green Filler via Photopolymerization
## 1 Introduction  
Additive manufacturing, commonly known as 3D printing, is an advanced technology that enables the fabrication of 3D objects by layering materials in a controlled manner [1]. The emergence of 3D-printed polymer materials has significantly transformed the manufacturing industry [2], enabling creating complex and customized designs [3]. This innovation has found applications across multiple sectors, including aerospace [4, 5], healthcare [6], and consumer goods. In aerospace, 3D printing is used to produce lightweight and intricate components [7], whereas in healthcare, 3D printing enables the development of custom implants and prosthetics [8, 9]. The ability to rapidly prototype and manufacture customized parts makes additive manufacturing an essential tool for modern production processes. Recent advancements in 3D printing have focused on enhancing the properties of polymer materials [3], leading to the development of stronger, more flexible, and more heat-resistant materials. These improvements have expanded the range of applications and have enabled the production of high-performance components across various industries. One critical aspect of these advances is the integration of composite materials, particularly fiber-reinforced polymers, which offer superior mechanical properties. However, these materials present challenges in terms of recyclability and end-of-life management [10]. The difficulty associated with recycling conventional fiber-reinforced composites has prompted research into more sustainable alternatives. The growing emphasis on environmental sustainability has driven efforts to develop biobased and biodegradable polymer composites. The transition to eco-friendly materials is aligned with global sustainability trends and corporate social responsibility initiatives [11]. One promising approach involves incorporating biomass waste into polymer composites via 3D printing techniques [12; 13; 14; 15; 16]. By using agricultural biomass waste as an additive, it is possible to create sustainable materials with improved mechanical properties while reducing reliance on non-renewable resources [17]. This strategy also supports circular economy principles by repurposing waste materials into valuable industrial products [18; 19]. Biochar, a carbon-rich material obtained by the pyrolysis of biomass waste, has gained increasing attention as a sustainable reinforcement for composite materials [20]. Because of its high surface area, porosity, and stability, biochar enhances the mechanical and thermal performance of polymer composites [21; 22; 23; 24; 25]. These improvements include increased tensile strength, elastic modulus, and resistance to thermal degradation. Additionally, biochar-based composites offer environmental benefits and can serve as effective adsorbents for wastewater treatment [26; 27; 28] and catalysts for clean energy applications [29; 30]. The biodegradability of biochar depends on the polymer matrix, making it a viable option when combined with biodegradable resins [31]. Cork waste, a byproduct of cork production, represents a renewable and abundant source of biochar. Using cork-derived biochar as a reinforcement material in polymer composites can reduce the environmental impact of cork waste while introducing new opportunities for resource conservation [32; 33; 34]. The integration of cork biochar into polymer matrices enhances the mechanical properties and promotes material fabrication sustainability. Despite its potential, research on the use of cork biochar in 3D-printed photopolymers remains limited. This study aimed to bridge this gap by investigating the feasibility of incorporating cork biochar into photopolymers via vat photopolymerization. To the best of our knowledge, this is the first study to successfully integrate cork biochar into a photopolymer using vat photopolymerization techniques, such as stereolithography (SLA) and digital light processing (DLP). These methods use photopolymer resins, but they differ in how the resin is cured [35].