RicePrintopia

Abstract

Rice is a vital food source for more than half of the global population, particularly in Asian countries. Among the four primary rice types traded and cultivated worldwide, white-milled rice stands out. Interestingly, global consumption of milled rice reached a staggering 523.9 million tons from July 2023 to July 2024, generating rice husk waste, a topic addressed in the U.S. Rice Sustainability Report.

Annually, about 120 million tons of rice husk are produced following the separation from the whole rice paddy. This translates to roughly 0.28 kilograms of rice husk generated per kilogram of milled white rice. Rice Husk, a byproduct of the rice production milling process. Universally abundant in rice-growing nations, rice husk contains 30% to 50% of organic carbon and an additional 20% to 25% of lignin within its composition. Lignin, one of the many components of rice husk, is a byproduct. Lignin emerges as a significant waste material with considerable economic potential for various high-value bio-based products. Characterized by its highly branched phenolic polymer structure, lignin comprises 15% to 30% of lignocellulose biomass by weight. Its hydrophobic properties enable effective binding, distinguishing it from cellulose. Notably, lignin presents an opportunity for enhancing the Mechanical Properties and Thermal Properties of PLA filaments. 

On the other hand, 3D printing, also referred to as additive manufacturing, is a transformative process that brings digital designs to life by creating tangible three-dimensional objects. The process involves utilizing low-melting-point polymers, such as polylactic acid (PLA), polyamide (PA), acrylonitrile butadiene styrene (ABS), and polycarbonate (PC), as additive materials for the printing process. Nonetheless, 3D printing encounters a significant challenge which is the structural integrity of the printed objects, particularly the spaces or gaps between individual layers. Unlike objects produced using conventional injection molding techniques, the mechanical strength of 3D-printed items is comparatively weaker. Additionally, PLA exhibits limitations in terms of mechanical robustness when contrasted with ABS, PA, and PC, which boast a more resilient molecular chain structure. However, PLA is the only biodegradable printing material as compared with others. Hence, this study chose PLA as a composite material to compare the mechanical strength of an object before and after adding lignin. 

This study centers on extracting lignin from rice husk. The extracted lignin will be blended with PLA pellets during the PLA filament production process. This investigation aims to analyze the mechanical and thermal properties of the resulting lignin-based PLA biocomposites, specifically the Elongation of Break and Young’s Modulus.

Keywords: 3D Printing, PLA, Polylactic Acid, Rice Husk, Lignin, Lignin Cellulose

Problem Statement

The escalating generation of rice husk waste has become a pressing environmental concern, necessitating innovative solutions to address the associated challenges. As rice husk waste continues to mount, its conventional disposal methods, notably through burning, have raised substantial environmental concerns, resulting in detrimental air pollution and long-term environmental harm. In this context, the underutilization of the significant lignin content present in rice husks, typically ranging between 20-25%, presents an untapped resource for addressing these issues. The potential applications of this lignin resource have remained largely unexplored, offering an avenue for more sustainable waste management practices. 

Furthermore, a noteworthy consideration in this research is the potential trade-off between mechanical strength and thermal properties in polymers. It is a common observation that as polymers are enhanced in terms of mechanical strength, their thermal properties tend to decrease. This presents an intriguing challenge for the research, as it involves striking a balance between these two essential aspects while exploring the possibilities of utilizing lignin to enhance the properties of rice husk-based materials.

Research Objective and Aim

To explore the potential of Rice Husks, a waste product, for use in 3D printing applications:

This objective aims to investigate the possibility of utilizing Rice Husks, which are typically discarded as waste, as a valuable resource for 3D printing. By identifying the composition and properties of Rice Husks, the researchers can determine if they can be processed and incorporated into 3D printing filaments.

To enhance the mechanical properties, such as Young's modulus, tensile strength, Yield Strength and Maximum force at entire areas of polylactic acid (PLA) filament by incorporating extracted lignin from Rice husk extraction:

The aim of this objective is to improve the mechanical performance of PLA filament, a commonly used material in 3D printing, by incorporating extracted lignin from Rice Husks. By modifying the PLA filament with adding lignin, we intend to enhance its Young's modulus, tensile strength, Yield Strength and Maximum force at entire areas

To improve the flow and heat transition temperature of lignin:

This objective want to achieve some aspect:

• Lignin has a high heat transition temperature and resistance to flow, which makes it unsuitable for direct use as a filament in 3D printing.

• By improving the flow properties of lignin, it can be processed more easily during filament extrusion, allowing for better control over the printing process.

• Enhancing the heat transition temperature of lignin ensures that the printed objects can withstand higher temperatures without deforming or losing their structural integrity.

• These improvements make the resulting materials more suitable for various applications, including healthcare applications like wound healing.

Research Question

To explore the potential of Rice Husks, a waste product, for use in 3D printing applications

• What are the key characteristics of Rice Husks that make them suitable for 3D printing applications?

• How can Rice Husks be processed and transformed into usable materials for 3D printing?

• What are the potential applications of Rice Husk-derived materials in 3D printing?

To enhance the mechanical properties, such as Young's modulus, tensile strength, Yield Strength and Maximum force at entire areas of polylactic acid (PLA) filament by incorporating lignin extracted from Rice Husk

• How does the addition of lignin extracted from Rice Husk affect the mechanical properties of PLA filament?

• What is the influence of different ratios of lignin to PLA on the mechanical properties of the resulting filament?

To examine the thermal and mechanical, properties of PLA-based filaments with different formulations of PLA and lignin, specifically tailored for fused deposition modeling (FDM) 3D printing applications

• What are the effects of of PLA and lignin on the mechanical properties of the resulting filaments?

To improve the flow and heat transition temperature of lignin

• How can the problem of flow and heat transition temperature of lignin be solved?

*All graphs, illustrations, and references are available in the “Website” section of the proposal.

1. Preparation of Materials

Essential components were sourced from various suppliers to ensure the accuracy and consistency of the experimental process. The Polylactic acid (PLA) 2003D pellets, a fundamental element of the research, were thoughtfully provided by NatureWorks Co. Ltd., ensuring a reliable and standardized basis for the ensuing experiments. Additionally, IIUM Laboratory played a pivotal role by supplying the necessary chloroforms, which were integral to the liquefaction of poly(lactic) acid pellets when they were combined with lignin. These chloroforms, obtained from IIUM Laboratory, were instrumental in achieving the desired properties in the materials utilized. The rice husks, specifically White Milled Long-Grain Rice, were responsibly sourced from Wellgrow Horti Trading, ensuring that the raw material used in the experiments met the required specifications. For various chemical processes, including the Soxhlet extraction and lignin extraction phases, N-HEXANE (BENDOSEN), ETHANOL ABSOLUTE DENATURED (HMBG), and Sulphuric Acid 3% w/v Solution (R&M) were indispensable reagents, thoughtfully provided by ChemBio Technology Sdn Bhd. These high-quality chemicals not only facilitated the effective execution of the experimental procedures but also contributed to the overall accuracy and reliability of the results. This careful selection of materials and components from reputable sources underscores the meticulousness and precision with which the study was conducted.

2. Preparation of Organosolv Lignin from Rice Husks

The preparation of Organosolv Lignin Powder was a meticulous process that involved several precise steps to extract this valuable substance from rice husks. It all began with the initial phase of husk cleaning, employing a stringent 1 mm net to meticulously sift out contaminants such as bugs and silica. This crucial cleaning step laid the foundation for the subsequent procedures, which avoid disturbance of the extraction process.

3. Removal of Wax, Lipids and Proteins from Rice Husks with Soxhlet Extraction Methods for Preparation of Rice Husks

Moving forward in the carefully orchestrated procedure, the rice husks underwent a meticulous step, namely the Soxhlet extraction, all conducted under the controlled environment of a specialized fume hood. This extraction process entailed the precise utilization of a meticulously calibrated mixture comprising n-hexane and ethanol, executed at an exacting temperature of 150°C. The apparatus employed for this reflux operation encompassed a Condenser, a Round Bottom Flask, a Soxhlet Extractor, Condenser, and a Mercury Thermometer, all seamlessly integrated to ensure precision. Furthermore, a precautionary measure was implemented by covering the tips with rubber stoppers, while a minute hole was thoughtfully punctured by a needle to facilitate the release of pressure during the extraction process. The Soxhlet Process was executed for a duration of 24 hours individually for each chemical solvent, commencing with n-hexane and followed by ethanol, until the solution achieved a state of pristine clarity. The overarching goal of this intricate operation was to effectively and comprehensively remove wax, lipids, and proteins from the rice husks, thereby ensuring that the resultant extracted material would meet the stringent criteria for purity, aligning with the desired standards for Organosolv lignin preparation.

4. Extraction of Lignin using Organosolv Extraction Technique

The fundamental essence of the methodology centered on the meticulous extraction of lignin from rice husk, a process essential for producing Organosolv lignin. This intricate procedure commenced with the formulation of a specialized solution, meticulously crafted with precision. The concoction consisted of 75% ethanol, mixed in a precise ratio of 75 ml, alongside 25 ml of distilled water, resulting in an ethanol-water solution, essential for husk material swelling. Additionally, a catalyst, in the form of 3.0% v/v sulfuric acid (3 ml), was gently introduced using a syringe without metal tips, ensuring precise control. The next pivotal step involved subjecting this solution to an extensive 24-hour reflux process, steadfastly maintained at a constant temperature of 150°C. This prolonged duration was of paramount importance, as it facilitated the complete and thorough liberation of lignin from the rice husk matrix. The apparatus employed for the reflux process included a round bottom flask, a condenser, and a heating plate, all meticulously orchestrated to bring about the successful extraction of Organosolv lignin, a key element in this sophisticated process.

5. Gravity Filtration and Drying Process to solid Organosolv Lignin

Following the meticulous completion of the reflux process, the extraction solution underwent a crucial phase in the methodology: the gravity filtration process. This pivotal step played an indispensable role in the removal of any residual husk material, thereby yielding a solution that was markedly enriched in lignin content, which adhered to the filter paper with remarkable efficacy. This separation of lignin from the myriad other components marked a significant milestone in the progression of our process, exemplifying the successful isolation of this valuable constituent. This separation procedure was facilitated through the employment of a specialized apparatus, comprising a filter funnel, precision-grade filter paper, and a carefully selected beaker, each of which contributed to the precision and success of this crucial phase in the preparation of Organosolv lignin.

The ultimate step in this extensive procedure entailed converting the lignin solution into a practical powder form. This was achieved through a meticulously controlled and gradual evaporation process, resulting in the formation of solid lignin on a hot plate placed over a petri dish. The solid lignin was subsequently scraped off, and the newly formed lignin solids underwent further drying, a critical phase aimed at ensuring their stability and suitability for subsequent use. The drying procedure was carried out in an oven, precisely maintained at 40°C, and extended over a 24-hour period.

6. Preparation of Lignin-PLA Bio-Composites

The PLA pellets, having been oven-dried at 60°C for a minimum of 3 hours, are melted in chloroform and stirred thoroughly on a hot plate for 4 hours, with an aluminum foil and tape cover in place. Following this 4-hour period, the PLA solution is poured into the first petri dish containing pure PLA, while the remaining PLA solution is mixed with Organosolv lignin and stirred on the hot plate for 15 minutes before being poured into the second petri dish. Both samples are then allowed to dry over the course of a single day.

*All graphs, illustrations, and references are available in the “Website” section of the proposal.

Preparation of Rice Husks

Physical and Chemical Properties of Test Results for Washed Rice Husks and Unwashed Rice Husks Washing Water

• Unwashed RH shows a greater concentration of total dissolved solids compared to washed RH.

• Total dissolved solids (TDS) describe the inorganic salts and small amounts of organic matter present in solution in water. (Water, Sanitation, Hygiene and Health (WSH), 1996)

• Washed RH: Undergo a pre-washing process to remove dust and some loose contaminants. Their wash water contains fewer dissolved solids as most have already removed. TDS meter reading for wash water is lower due to fewer dissolved minerals and organic matter.

• Unwashed Rice Husks: Retain their natural coating of dust, dirt, plant sap, and other organic matter. When washed, these materials dissolve in the water, increasing the TDS concentration. The TDS meter reading for wash water is higher due to the presence of various dissolved contaminants.

• The concentration of nitrate (NO3) in the wash water of unwashed rice husks is greater than that observed in the corresponding graph for washed rice husks wash water (Yee Aquarium Test Paper 7 in 1).

• Rice husks naturally contain nitrate, absorbed from the soil through the rice plant.

• This nitrate serves as a nitrogen source for the plant's growth. (Xiao et al., 2023)

• Nitrate tends to accumulate on the outer layers of grains, including the rice husk. This is because it enters the plant through the roots and is transported upwards via the phloem. (Yuan et al., 2022)

• Rice Husks Sample contain soil, which Soil contains nitrate that essential for plant growth and is converted to protein in the plant at about the same rates as it is absorbed into the root system. (Colorado State University Extension, 2015)

• Sources of soil nitrate include decomposing plant residues and animal manure/compost, chemical fertilizers, exudates from living plants, rainfall, and lightning. (Soil Nitrate for Soil Health | South Dakota Soil Health Coalition, 2020)(Soil Quality Indicators - Natural Resources Conservation Service)

• Washing the rice husks simply removes the surface layer, including the accumulated nitrate. This reduces the overall nitrate content in the wash water compared to unwashed husks.

• The Error Bar for R, G, B Value serving as a quantitative testament to its darker color compared to the wash water obtained from the washed RH.

• Pigment Release: Unwashed rice husks retain various pigments naturally present in the grain and hull, such as brown melanin, yellow carotenoids, and red anthocyanins. When unwashed husks come in contact with water, these pigments leach out, coloring the wash water darker.

• Dirt and Contaminants: Rice fields and storage conditions can expose husks to dirt, dust, and organic matter. Unwashed husks retain these contaminants, which contribute to the dark color of the wash water.

• Oxidation: Some naturally occurring compounds in rice husks, like phenolic acids, can undergo oxidation when exposed to air and water. This oxidation process generates darker colored compounds, adding to the overall darkness of the wash water. (Krishnarao et al., 2001)

Identification of Lignin Extracted through FT-IR and uv-vis Spectroscopy

• Because of the various chromophore groups present in the lignin structure, the analysis of UV-vis spectra serves as a crucial tool for assessing purity and confirming the presence of its primary cinnamyl acids.

• The band in 283nm is relative to conjugated and unconjugated phenolic groups.

• The band in 313 nm is attributed to the ferulic acid and p-cumarylics association.

• Contaminants presence such as silica result in a weak increase in absorptivity of both band in 280 nm and 313nm.

• Both samples showed similar absorption bands at two main absorbance regions around 1745 cm-1 and 2880-3000 cm-1 indicating that all samples have similar chemical compositions.

• The characteristic carbonyl stretching around 1745 cm-1 is attributed to C=O stretching vibration while peaks from 2880-3000 cm-1 are associated to the asymmetric and symmetric stretching vibration of CH3 group. The peak at 1453 cm-1 corresponds to CH3 anti-symmetric bending vibration. The peaks at 1383 cm-1 and 1359 cm-1 are associated to the deformation, symmetric, and bending mode of the CH group. The peaks at 1041, 1081 and 1180 cm-1 are attributed to C-O stretching vibrations. The band 754 and 868 cm-1 ascribed to the crystalline and amorphous phases of PLA, respectively. (Rahman et al., 2021b)

• The PLA-Lignin bio-composite exhibits some peak shifting as well as intensity changes, which may indicate the intramolecular interaction and compatibility of the PLA and lignin.

• The notable difference may be observed on several peaks in PLA was neutralized further.

• The peaks band can be highlighted between 3400 and 3600 cm−1 and indicate the presence of a hydroxyl group, O–H (Zaidi et al., 2023).

• These interactions and changes of peaks indicate the miscibility of all components that mainly consists of PLA and lignin.

Mechanical Characterization of Lignin-PLA Bio-Composites with Universal Testing Machine

• The stress-strain curve graphs illustrate the mechanical characteristics of both materials, providing insights into Young’s Modulus, Tensile Strength, Yield Strength, and Max_Force at the Entire Area.

• The incorporation of lignin into the PLA filament leads to a rapid enhancement in Young’s Modulus and Tensile Strength, signifying stiffness and resistance to elastic deformation. This results in the material's ability to withstand substantial pulling forces before reaching a breaking or tearing point.

• This behavior is anticipated due to the presence of lignin, which hinders the formation of a long-range continuous phase in PLA.

• The elevated Yield Strength of PLA-Lignin implies an increased capacity to endure stronger forces before experiencing bending, stretching, or compression. Furthermore, it retains deformation even after the applied force is removed.

• PLA exhibits brittleness, weakness, and fragility, attributed to its lower maximum force at the entire area compared to PLA-Lignin. This is exacerbated by the homogeneous mixing of PLA with lignin, facilitated by the hydrophilicity of lignin.

Thermal Characterization of Lignin-PLA Bio-Composites with Thermogravimetric Analysis and differential Scanning Calorimetry

• The PLA–lignin composites exhibit a two-step degradation process.

• While PLA starts decompose at around 150 to 400 ◦C, lignin started decomposed above 450 ◦C.

• The multistep decomposition occurs due to the structural heterogeneity of lignin – the various functional groups and structural elements start to cleave off at different temperatures reducing the total mass (Mimini et al., 2019).

• The decomposition degree of PLA composites is higher than PLA-Lignin with highest residue percentage and total weight loss.

• PLA-Lignin has low DTGmax indicates a slower rate of material decomposition compared to PLA thus caused stronger PLA-Lignin thermal properties.

• TGA thermogram shows that filaments with addition of lignin have a significant change to higher temperature for initial degradation temperature and final degradation temperature compared to neat PLA filament.

• It was noticed that the Tₒ of neat PLA occur at around 114.98 ◦C and decomposed completely at 486.88 ◦C.

• Thermal decomposition of the PLA-Lignin occur initially at higher temperature of 124.81 °C showing good thermal stability of the composites.

• Since PLA is a semi-crystalline polymer, its thermal properties are strongly dependent on its crystallinity behavior which can be observed from the cold crystallization temperature.

• Cold crystallization is an exothermic process that is observed due to the amorphous fraction of the PLA matrix to be partly reorganized or crystallized.

• Tcc of PLA is commonly occurred between glass transition temperature and melting temperature (Rahman et al., 2021).

• The addition of lignin had reduced the rate of crystallization of PLA, hence the Cold Crystallization Temperature occurred at higher temperature.

• Higher Cold Crystallization Temperature will give the ability to the PLA to retain the microphase distribution in the amorphous region even at high thermal stress.

• Higher Glass Transition temperature of PLA-Lignin can maintains its rigidity and strength over a wider temperature range, offering improved resistance to heat.

• Melting temperature of PLA is increased by addition of lignin, which crucial for high-temperature applications.

• The results does not have huge significant difference due to agglomeration, poor dispersion of reinforcements as well as due to existence of voids between the lignin and PLA matrix.

*All graphs, illustrations, and references are available in the “Website” section of the proposal.