Grantee Research Project Results
Final Report: Conversion of crop waste into construction material
EPA Grant Number: SU839850Title: Conversion of crop waste into construction material
Investigators: Venkatadriagaram, Sundararajan , Lin, Dayong , Templer, Shawn , Ortiz, Erica , de Bleecker, Yann , Aoki, Genevieve , Orluck, Dylan
Institution: University of California - Riverside
EPA Project Officer: Page, Angela
Phase: I
Project Period: November 1, 2019 through October 30, 2020 (Extended to October 30, 2022)
Project Amount: $24,998
RFA: P3 Awards: A National Student Design Competition Focusing on People, Prosperity and the Planet (2019) RFA Text | Recipients Lists
Research Category: P3 Awards , P3 Challenge Area - Sustainable and Healthy Communities
Objective:
The objective of this project is to reuse crop waste, specifically wheat straw, and convert it to a construction material that can provide a substitute for conventional gypsum-based drywall. The wheat straw is converted into pulp which is then processed into dry-wall boards. The benefits of this new drywall product are that it is not only be comparable to the traditional drywall, but will have benefits like higher moisture resistance and biodegradability upon disposal. The goal is to provide an environmentally friendly alternative to conventional dry-wall, reuse crop waste and prevent health risks associated with the manufacturing, installation, teardown, and disposal of the traditional drywall.
Summary/Accomplishments (Outputs/Outcomes):
A process to convert the wheat straw to pulp has been designed on the basis of the Kraft process that is used to convert wood to wood pulp. The steps for converting wheat straw to the boards are as follows:
1. The raw material for the process is wheat straw in the form of straw bale. The straw was screened and washed in order to remove unwanted material and contaminants.
2. The straw was cut using a blender in order to cut pieces that are approximately 2 cm in length order to ensure that downstream steps can be carried out with a uniform starting material. Longer straw fragments were screened out and passed back into the blender. The key control parameters in this step is the time required for blending and the final length to which the straw is cut.
3. The straw was soaked in a cooker containing hot water for about 60-150 minutes. The temperature of the hot water was be maintained at approximately 80°C. The hot water treatment reduces the ash content of the wheat straw and also dissolves some of the water-soluble carbohydrates. Pretreatment of the straw improves the defibration of the straw which increases the yield of pulp. This initial pretreatment of the straw, softens the fibers and decreases the cooking time in the digester causing a greater yield of pulp.
4. The softened straw was then fed into a stainless-steel pressure cooker that contains a cooking liquor, this is the refining step where we bring the wheat straw to a fine product. The straw was added into the cooker with the cooking liquor containing potassium hydroxide, ammonia that is diluted with deionized water. Cooking was performed at a temperature of 100 - 155 °C for about 60 minutes and is followed with 45 minutes of holding time at the same temperature. Adding potassium hydroxide not only reduces the contamination levels that are normally found in pulp black liquor but also increases the amount of nutrients found in the liquor.
5. After the refining process, the cooked wheat straw is placed on a screen to separate large pieces such as fibers that clumped together as well as any wheat that did not disintegrate. The substances that do not pass through the screen are then reloaded into the digester for refining
Lastly a filtration process is done to separate the black liquor from the pulp. The product is then washed to remove residues, and then dried.
7. Additives such as seaweed powder, waxes and thermoplastic powders are added and mixed to the pulp to improve the mechanical, thermal and chemical properties.
8. The pulp is placed in heated rectangular molds and are pressed to form the final board. The first hot press cycle is set to a high temperature. It is the most critical step because it quickly removes humidity/water from the pulp-resin material and also allow the resin binder to randomly diffuse among the material, thereby improving adhesion between pulp particles.
9. The pulp-resin material is removed from the press cycle and cooled with air of low humidity that is blown over the mold. Due to the high temperature gradient and air (low humidity), heat is released from the material quickly and results in a sudden contraction.
10. The material is then pressed in a second and third hot press cycle with a slightly lower temperature and held for longer times to allow the resins to cure.
11. After the hot press, allow the strawboard to be cooled to ambient temperature.
Figure 1: Process for producing pulp from wheat straw
Figure 2: Process for converting pulp to dry boards
Conclusions:
Some key findings include:
1. The choice of binders such as waxes need to be explored to reduce flaking of the pulp, to inhibit mold growth and to improve the integrity of the final product.
2. The use of thermoplastic powder was most effective in obtaining a board with adequate integrity.
3. There are numerous parameters involved in each of the steps outlined above. The parameters involve both categorical and continuous variables. Categorical variables include parameters such as the choice of binders while continuous variables include parameters like the temperature and time for cooking the straw. Thus, a design of experiments approach is necessary to obtain the right mix of parameters.
4. Before a statistical design of experiments outlined above can be implemented, it is important to explore the feasible space of parameters. This itself can be difficult and time consuming when developing a new process or when adapting an existing process to a different material.
5. ASTM standards that are used to characterize dry-wall may be used to characterize the alternative material, although some tests have to be adapted for small-scale testing in university laboratories.
The project yielded the design of a process that could produce an alternative to conventional dry-wall from wheat-straw. It also led to the design and fabrication of material characterization techniques. Experience with implementing the process showed promising results. After extensive exploration of production condition, a material that had sufficient integrity and strength was developed; however further development and characterization is needed to determine and optimize the process parameters and to characterize the material for mechanical, thermal and chemical properties. We note that there are a large number of parameters that influence the final product because the overall process involves several sub-processes, each of which has numerous parameters that can be adjusted, controlled and optimized. The economics of large-scale production was studied in a simulation study and was found slightly more expensive than conventional dry-wall – a trade-off that might be acceptable for an eco-friendly alternative.
Supplemental Keywords:
Sustainable materials, green buildings, eco-friendly, green engineering, resource recycling, environmental substitute, waste-to-value, sustainable construction.Progress and Final Reports:
Original AbstractThe perspectives, information and conclusions conveyed in research project abstracts, progress reports, final reports, journal abstracts and journal publications convey the viewpoints of the principal investigator and may not represent the views and policies of ORD and EPA. Conclusions drawn by the principal investigators have not been reviewed by the Agency.