4Th Annual R&D Student Competition: Manufacturing Process of Mycelium-bound Biocomposite Sandwich Structures Project Report

Transcription

1 4Th Annual R&D Student Competition: Manufacturing Process of Mycelium-bound Biocomposite Sandwich Structures Project Report Biocomposites Manufacturing Research Team Center for Automation Technologies and Systems (CATS) at RPI 1. Problem Statement Advanced polymer matrix composites (PMCs) are comprised of strong, rigid reinforcements (e.g., glass and carbon fibers) bonded together by durable polymers (e.g., epoxy, polyester, nylon) to form laminate skins, which can then be made into sandwich structures using lightweight cores (e.g. honeycomb, balsa). These materials provide significant benefits over conventional engineering materials (e.g., steel and aluminum alloys) such as high stiffness-to-weight and -strength ratios and tailorable mechanical, thermal, and physical properties. While there is potential for significant growth of PMC use in a myriad of industrial markets [1], there are also significant issues that limit this growth as well. Because they are either derived from non-renewable resources (e.g., reinforcements and resin made from petroleum and natural gas) or harvested from limited natural resources (e.g., most balsa wood used for cores is harvested in tropical regions of South American such as Ecuador), constituent materials of most conventional composite material systems are typically expensive and subject to price and supply fluctuations. Manufacturing costs for composites are also high because of industry s reliance on manual processing. Furthermore, synthetic composites have poor end-of-life options due to the difficulty of separating the mixed material back into its constituent parts. The only economical options currently are burning for fuel, landfilling, and in rare cases, regrinding to act as filler material. An ideal situation for companies interested in designing and manufacturing sustainable products would be the availability of composite materials consisting of all bio-derived constituents and made using bio-inspired, low-energy processes. This idea has been put 1

2 forward by many researchers (e.g., Ref. [2]) and serves as the inspiration behind the work described in this project report. 2. Project Summary and Background The known history of natural fiber-reinforced matrix dates back to about 3,000 years ago when house walls were made using straw-reinforced clay. By evolution, animals and plants employ composites in many biological structures (e.g., wood, shells, bone, teeth, horn and hides), where high mechanical strength/stiffness and low weight materials are required. In nature, these composites are produced at low temperature and pressure and serve as bio-inspired templates for mankind to mimic in designing and manufacturing synthetic or semi-synthetic materials. In the early 20 th century, specifically the 1930s, Henry Ford [3] had the forward looking idea to investigate natural materials for use in automobiles, such as chicken bones, that exhibited high specific strength. A variety of natural materials was investigated in his laboratory including chicken bones, onion, garlic, cabbage, and cornstalks. At the beginning of 1942, Ford had his first car prototype made from hemp fibers, which unfortunately did not pass into a general production due to economic conditions at that time. Since then, natural fibers continued to grow in many others industries, such as goods industry, aeronautic industry, etc. Some other applications include: Brother and McKinney reportedly making plastics using soy protein and various cross-linking agents [4] Drzal et al. finding the combination of bio-fibers like kenaf, hemp, flax, jute, henequen, pineapple leaf fiber and sisal with polymer matrices can be used in automotive applications [5] Flanigan et al. using natural fibers to replace either part or all of the glass fiber reinforcement used in the composites in order to increase the bio-content [6] Ulrich Riedel and Jörg Nickel have been working with natural fiber composites for 2

3 constructive parts in aerospace, automobiles, and other areas. They did application researches on designer office chairs, door paneling elements, pultruded support slats, safety helmets, and interior paneling for track vehicles, etc. [7] and The Havilland DH 88 Comet aircraft used in the World War II that had a fuselage made of unidirectional, unbleached flax yarn impregnated with phenolic resin and cured under pressure. Mycelium, which is the vegetative part of a fungus, consisting of a mass of branching, thread-like hyphae [8], can act as a natural binder for biocomposite materials. It digests and bonds to the surface of damp agricultural byproducts in 5-7 days without additional energy input to adequately colonize reinforcement fibers and core material, thereby acting as a natural, self-assembling glue [9]. A SEM image of mycelium hyphae growing on a natural fiber is shown in Figure 1(a). Following colonization, water is driven off and the mycelium is inactivated (killed) by drying the composite at high temperature (>80 C) in a convection oven or on a thermal press for a certain period of time. The resulting inactivated fungal network of threadlike cells, essentially the roots of mushrooms, bind together natural fiber reinforcement to form laminates (bound layers of reinforcement) and organic waste used as core material to form sandwich structures (attaching two thin but stiff skins to a lightweight but thick core), as shown in Figure 1(b). These mycocomposites, shown in Figure 1(c), are reasonably rigid without infused resins: longer colonization leads to stiffer and stronger structures, and a smoother surface can also be achieved through full colonization [10]. To make truly structural sandwich parts, the myceliated core and dry reinforcements can be used as preforms for resin infusion processes (e.g., resin transfer molding). Mycocomposites are inherently safe the material is stable when exposed to high temperatures ( C ignition point range) or ultraviolet radiation, and the use of vegetative tissue prevents the formation of spores (a potential allergen and friable particle) if it 3

4 is made inactive (i.e. killed) before fruiting bodies form. (a) (b) (c) Figure 1: (a) SEM image of mycelium hyphae growing on a natural fiber [5], (b) schematic of biocomposite sandwich and laminate structures, and (c) picture of a mycocomposite sandwich structure. Ecovative Design, LLC and the CATS Composite Research Lab at Rensselaer Polytechnic Institute are developing innovative and unique mycocomposite materials and associated manufacturing processes to address this need. It is now possible to make biocomposite laminates and sandwich structures and preforms using sustainable materials and inherently low energy processes with environmentally benign end-of-life options, i.e. getting closer to the ideal. Referring to Figure 2, the current manufacturing concept envisioned to make these sandwich structure biocomposites includes: 1) cutting natural fiber reinforcement in textile or mat form to the desired ply shape; 2) pre-impregnating one of more plies at a time with a natural glue; 3) forming, sterilizing, and solidifying pre-impregnating reinforcement into integral tooling; 4) filling integral tooling with agricultural waste pre-colonized with mycelium; 5) allowing the growing mycelium to bind together and grow into all constituent components under the right conditions to form a completely unitized sandwich preform or part; 6) drying and inactivating (killing) the mycelium-bound structure; and 7) 4

5 infusing and curing natural resin into the reinforcement skins if increased part stiffness is required. Compared to the traditional manufacturing method of synthetic composite preforms, there is significantly less energy required with this approach. Figure 2: Manufacturing steps for mycelium-bound biocomposite sandwich structures [11] As Steps 1-3 have been studied in prior work [10, 11], and Steps 4-6 are already well developed manufacturing processes at our cooperative company, this project will be focusing on Steps 4-7 whereby the biocomposite preform is fabricated and then vacuum infused and cured with bioresin in place. 3. Relationship to Sustainability The main advantages of mycelium-based materials made using natural fibers (e.g., kenaf, jute, hemp, flax, bamboo, and sisal) over traditional synthetic composites are low cost, low density, competitive strength, tensile and impact mechanical properties, reduced energy consumption, the potential for CO 2 sequesterization if done at large scale, and perhaps most important of all, biodegradability [10]. The low-embodied-energy production process used for mycocomposites makes them cost competitive with synthetics, but the material is inherently sustainable since it comes from completely renewable sources and will biodegrade under the proper conditions or can be recycled into feedstock for packaging or composite core material (thus diverting waste from landfills). 5

6 If made commercially available, the new biocomposite sandwich material replacing plastic parts such as automobile interior panels or exterior bumpers will lead to a reduced or slower increase in traditional non-recyclable materials consumption. Such solid wastes will be reduced to have current landfills last for a longer time, and reduce toxic gas release if the solid waste is burnt for energy. 4. Materials and Methods 4.1 See-Through VIP Mold to Observe Resin Flow Behavior In order to develop the proper resin transfer mold that can infuse the part adequately, it is most important to lean the resin flow behavior inside the model under a vacuum pulling (e.g. negative pressure). This is why a temporary simple resin infusion mold was designed using SolidWorks software and its physical prototype was built (Figure 3). Acrylic plates are chosen as the material for the mold as they are easy to cut using a laser cutter and then assembled together using acrylic welder solvent. Its transparent property allows the researchers to observe if the resin has fully infused the part. The see-through VIP model was finished by the team by the end of December 2014 and the resin flow configuration experiments were performed afterwards using resin analog (i.e. corn syrup as there is no need to cure the resin at this point). The best resin flow direction was found to be flowing in from the top center point and vacuum being pulled at the center bottom port (Figure 4). (a) (b) Figure 3: (a) CAD model of transparent VIP mold and (b) acrylic mold fabricated for preliminary resin flow studies 6

7 Figure 4: Four resin flow configurations with yellow arrows indicating resin flow directions. 4.2 Permanent Infusion/curing Mold Design and Fabrication The permanent heated resin infusion and curing mold was designed using SolidWorks software (Figure 5, left) and then fabricated using aluminum and 80/20 extrusions (Figure 5, right) based on the flow behavior study. Cartridge heaters and water cooling channels are embedded into the CNC machined mold for quick heating up and cooling down. The temperature of the mold is controlled by a Chromalox multichannel temperature controller. Mold release will be applied onto the mold s working surfaces for quick and easy separation before the curing process. The permanent mold was finished by the team at the end of February Myceliated Agri-waste Preforms Preparation Pre-grown mycelium cores using agri-wastes and mushroom mycelium were finished at the cooperative company. The growth tools (Figure 6) were also fabricated there using a thermal plastic former. The first batch was grown using the core material only so the reinforcement skins can later be applied with bioresin using a brush, and then placed onto both the top and bottom sides of the grown cores. The sandwich structure is then cured on a thermal press after which mechanical properties tests 7

8 were done on an Instron machine. Future batches will be grown directly with woven textile and be infused and cured in the resin transfer mold and then cure in place. Figure 5: CAD (left) and Physical Prototype (right) of the Permanent Resin Infusion/Curing Mold Figure 6: Mycelium Preform Growth Tools 4.4 Bioresin Benchmarking and Preparation The team preformed several formulation tests using bioresins from different brands and types and found the best formula that will meet the essential requirements for the new manufacturing process. The chosen bioresin is a mix of Agrol 2.0 rein (99% bio-based content), Agrol Diamond resin (86% bio-based content) with the MONDUR compound from Bayer. It has a pot life of 30 min after being mixed together, gels in minutes under elevated temperature, and cures overnight. Both team members worked together on all these aforementioned tasks and we would like to 8

9 acknowledge our advisor, staffs from both our lab system and our cooperative company for their help. 5. Results, Evaluation and Demonstration A new kind of biocomposites infused and then cured with natural woven plies sandwiching the myceliated agri-waste cores in the middle are to be made as the result of this project (Figure 7). Mechanical tests of such material are still pending due to the postponements in research processes, yet it is very likely to achieve the stiffness requirements for its desired usage. The density of the new material is 0.41 g/cm 3, while the density of the ABS plastic that are usually used as the interior panels for automobiles is 1.10 g/cm 3. The average vehicle uses about 150 kg of plastics and plastic composites versus 1163 kg of iron and steel currently it is moving around % of total weight of the car [12], 65.5 million automobiles were produced in the year of 2013, even if some of them are replaced with the new material in the future, millions of tons of plastics can be avoided, which means much less petroleum being used and less CO 2 being emitted into the air. A Life Cycle Assessment (LCA) is carried out to illustrate this more clearly. Figure 8 shows a LCA performed with the LCA calculator online, which calculates the equivalent CO 2 emissions for making 100 automobiles, each of them carrying 150 kg interior panels made from ABS plastic. The transportation assumption made here is that the panels either made from traditional ABS plastic or from the new biocomposites have to be shipped to the automobile manufacturer from a place that is 200 km away. The energy consumption during the product using phase really depends on the weight of all panels in the vehicle, and the heavier they are, the more fuel is to be consumed. Finally, for the disposal at the end of product life, little plastic in an automobile is being recycled or reused, comparing to the new biocomposites that can be fully recycled or biodegraded. This new concept will be presented using a poster, several samples of the new material made for the project, as well as some visual aids such as photos of the prototypes made as supplements. 9

10 Figure 7: Sample of Final Product Figure 8: LCA Comparison Analysis 100 Automobile Panels using the New Biocomposites or Traditional ABS Plastic 6. Conclusions A new manufacturing process for producing mycelium and agri-waste based biocomposites sandwich structures are developed, in order to be used as a replacement material for automobile interior panels and also other possible applications. The preform of this material is 100% green while high bio-contents are in its bioresin. Future work of this project would be to test the mechanical properties of the parts made according to the ASTM D7250/C393 standards. Also, the mechanical modeling work will be a plus in further understanding the material s behavior. Potential implementations of such material are not limited to the automobile industry but can also include insulation, structural biocomposites as well as sports goods, etc. 10

11 References [1] Growth Opportunities in Global Composites Industry , Lucintel, March [2] Mohanty, A.K., Misra, M., and Drzal, L.T., Sustainable bio-composites from renewable resources: opportunities and challenges in the green materials world, Journal of Polymers and the Environment, 10(1/2), April 2002, pp [3] Mohanty, Amar, Manjusri Misra, and Lawrence Drzal, Editors. Natural Fibers, Biopolymers, and Biocomposites. Taylor & Francis Group, ebook. [4] G. H. Brother and L. L. McKinney (1940) Ind. Eng. Chem. 32, [5] Drzal, Lawrence T., A.K. Mohanty, and M. Misra. "BIO-COMPOSITE MATERIALS AS ALTERNATIVES TO PETROLEUM-BASED COMPOSITES FOR AUTOMOTIVE APPLICATIONS." 2001 SPE ACCE PROCEEDINGS Web. 13 Jan < [6] Flanigan, Cynthia, Christine Perry, Ellen Lee, Dan Houston, Debbie Mielewski, and Angela Harris. Use of agriculture materials in flexible polyurethanes and composites for automotive applications SPE ACCE PROCEEDINGS Web. 13 Jan < [7] Riedel, Ulrich, and Jörg Nickel. "Applications of Natural Fiber Composites for Constructive Parts in Aerospace, Automobiles, and Other Areas." Trans. Array Biopolymers.. 1st ed.wiley-vch, Web. 4 Apr < [8] Website: accessed on Nov. 15, [9] Website: accessed on Nov. 15, [10] Jiang, L., Walczyk, D., Mooney, L. and Putney, S., "Manufacturing of Mycelium-based Biocomposites, SAMPE 2013 Proceedings, Oct. 30, 2013, pp [11] Jiang, L., Walczyk, D., McIntyre, G., A New Process for Manufacturing Biocomposite Laminate and Sandwich Parts using Mycelium as a Binder, ASC 2014 Proceedings, San Diego, CA, Sept. 8-10, [12] SZETEIOVÁ, K, AUTOMOTIVE MATERIALS PLASTICS IN AUTOMOTIVE MARKETS TODAY, pp < 11