A solution to improve the thermal efficiency of the exterior shell of a building using natural non-woven composite materials

Silkworm cocoons are a biological structure and a natural compound that develop over time and responds well to the environmental conditions for silkworms. Understanding the relationships of cocoon structure inspires the creation of composite structures such as low-weight, high-strength nonwoven bio composites. By means of a descriptive-analytical method and logical reasoning, in this study, in addition to introducing the cocoon structure, we try to offer materials as a non-woven bio composite, using sericin cocoon and natural fibers which for various reasons such as being light, non-polluted, abundant, and low-cost can be a suitable alternative to artificial fibers. These materials are recyclable and suitable in terms of stability and energy consumption; therefore, they can be used as thermal and moisture insulation. This function is simulated and analyzed for the hot and dry climate of Kashan city in the outer shell of the building using the Hani Bee energy analysis plugin in the Grasshopper environment. The results show that the proposed non-woven bio composite can help improve, by up to 12.7%, the thermal performance of the building and decrease the movement of heat between the inner and outer space compared to the same building without thermal insulation in its outer shell.


Introduction
The use of composites in architecture is in the early stages compared to their use in other industries. The reason for this is the lack of engineering standards in the building and the architects' lack of interest in using these materials. Structures that are made using natural composite materials are more compatible with the environment, which results in reducing energy consumption and carbon emissions during the production process, but the major drawback of composites with synthetic fibers is the lack of a solution for their recycling. [1] Research on eco-friendly composites made from natural fibers is important due to environmental compatibility and resource depletion concerns; Non-woven textiles are a part of these compounds that are connected without special makeup and texture and with the help of glue (matrix). One of these materials is the silkworm cocoon, which is a polymer of a single chain of silk fibers about 1,000 to 1,500 micrometers long, linked by sericin, which contains a protein that is about 75% of the weight of the cocoon and sericin, which is a water-soluble polymer. , constitutes 25% of its weight. [2][3]. Each layer of the silkworm cocoon has different mechanical behavior and proper performance against moisture, air flow, ultraviolet rays and impact. Considering the above, in this study, inspired by the two-component structure of the silkworm cocoon, a non-woven biocomposite composed of natural jute fibers and sericin is proposed due to its abundance and low thermal conductivity. The suggested materials can perform well in the building. Among other things, it can be used as thermal insulation in the outer shell of the building. In the continuation of this research, the performance of this thermal insulation in the outer shell of the building in hot and dry weather is analyzed by the Honeybee Grasshopper plugin and the results of this simulation are evaluated.
Research questions: 1. How does the study of the structure and materials of silk cocoons and natural fibres lead to a non-woven composite model? 2. How does the proposed natural fibre nonwoven composite model help to improve performance in buildings?

Non-Woven natural fiber composite model
In this paper, a non-woven composite model with natural fibers and sericin cocoon grafting is proposed and its structure will be described with a main process. The use of natural fibers is possible in many regions and countries due to their good thermal properties and favorable strength, lightness, recyclability and easy access. These fibers were used in building materials in the past, and today, with increasing environmental concerns, they have been used in several studies in the preparation of biocomposites. To choose natural fibers, you should first check them according to their design needs and compare their strengths and weaknesses. In this model, jute was considered as a natural fiber in the preparation of fibrous biocomposite due to its lower thermal conductivity than hemp and flax and the abundance of these fibers and the ability to grow in all regions. After choosing the fibers, the adhesive between the fibers is important, which leads to strength and strengthening of mechanical properties. Synthetic bonds have significant disadvantages, such as water absorption, which can reduce the useful life of composite materials, and due to the manufacturing process of composite materials, it consumes more energy. [4][5][6] In addition, as toxic substances, they cause side effects. [7] Therefore, sericin is a suitable alternative as a natural adhesive. In this research, sericin was considered as a binder between jute fibers to produce nonwoven biocomposites. The amount of sericin can be used up to 30 percent by volume, and the remaining 70 percent is made up of natural fibers. The manufacturing process starts with cutting the fibers to 1 cm length. Then the fibers are poured into a container and sericin solution is added to it and the solution is gently stirred to obtain a homogeneous dispersion of the fibers in the solution. After that, the prepared material is poured into a steel mold and the mixture is placed in a heat press to remove moisture and compress the fibers, to produce a compact composite panel.

Simulation of thermal behavior of nonwoven natural fibrous composite
To simulate the thermal behavior of a non-woven jutesericin composite like moisture and heat insulation, a shell view of the building was first presented. This layer is located as a thermal insulation on the outside of the building wall and the outer wall of the building is considered to be on the south side of the building. Architectural details of the building shell were selected to calculate structures without load bearing and reinforcing elements. To allocate materials to the designed shell components of the building, a 22 cm solid brick was considered for the exterior wall of the building and a 3 cm plate brick was considered for the facade covering. The coefficient of thermal conductivity of brick materials is 0.9 and the coefficient of thermal conductivity of the air layer between the bio composite thermal insulation and the facade cover is 0.026, in accordance with the numbers in Section 19 of the National Building Regulations. The thermal conductivity of non-woven jute biocomposite, which is proposed as thermal insulation with a thickness of 5 cm, was calculated based on Maxwell's formula. Right) The proposed model of shell façade -Fiber composite panels with natural fibers are placed on the outer shell of the building façade as a moisture and heat retarder. There should be a space for air conditioning between the façade cover and the composite. In this simulation, the hot and dry climatic conditions of Kashan city were considered.The climate of Kashan is hot for nine months of the year and cold only for three months of the year . For this reason, simulating and reviewing performance for the summer and warm months of the year is a priority. According to the statistics of Kashan meteorological station, August and July with an average temperature of 37 to 40 ° C are the warmest months of the year and January is the coldest month of the year with an average temperature of about -2 ° C .The average maximum temperature is 24.5 ° C and the average minimum temperature is 11 ° C .For this reason, the external temperature conditions of the building were considered in accordance with meteorological statistics and for its average temperature in the warm seasons of the year (+40) ° C. By determining the boundary conditions of indoor and outdoor environments, the hypothetical temperature inside 24 (equal to thermal comfort conditions) was determined.
Thermal simulation of the outer crust in Rhino and in the Grasshopper environment and its energy analysis was performed by the Honeybee plugin. Two modes were considered for the building shell. At first, the building shell was designed as a thermal insulator in the software environment without considering jute-sericin non-woven composite materials. In the second case, the proposed materials are placed in accordance with the architectural details of "figure 3", such as insulation in the building shell and between the covering materials of the facade and the building wall. Based on the output data of this simulation process, the amount of temperature difference in materials on the outside and inside of the building as well as the amount of heat transferred along surfaces in watts per square meter in Kelvin can be obtained. By comparing the two shell states of the building, by considering the non-woven bio composite insulation of jute as thermal insulation between the inner and outer walls and without considering that, the performance of the proposed materials in reducing heat transfer in the building can be obtained. The amount of temperature difference inside and outside the building and heat transfer of the wall surface in two modes of thermal simulation of the building shell, which was done in software, were obtained from the numerical outputs of the thermal analysis algorithm and can be seen in the table below. Percentage change of temperature difference between inside and outside layers (° C) 12.7% * First case: Building shell -inner wall and exterior **Second case: Building shell -inner wall and exterior and bio composite layer of jute-sericin as thermal insulation between them As shown in "figure 2" and in the table above, the temperature difference between the outside and inside of the building will be greater when the non-woven composite insulation layer of natural jute-sericin fibers is placed between the facade shell and the building wall. This means that the proposed non-woven bio composite materials can be effective in improving the thermal performance up to 1.2 ° C and also by considering the numerical rate of heat transfer in watts from the wall surface per m2, the value is 2.72 for the case of non-woven composite insulation with natural fibers. Jute and 2.28 w/ m2. °K for the case where the shell has non-woven composite thermal insulation . Therefore, the presence of a thermal insulation layer of jute bio composite will help to increase the thermal efficiency up to 12.7% compared to when the building shell is considered without thermal insulation. According to the obtained thermal analysis and the study of numerical values in this analysis, the presence of non-woven composite with natural fibers as a thermal insulator in the outer shell has a good performance and reduces the penetration of heat into the building.
Another point about this bio-composite is its performance comparison with commonly used mineral insulations such as fiberglass, mineral wool and expanded polystyrene. The thermal conductivity of this fibrous biocomposite is slightly higher than the three thermal insulators mentioned above, and this material, as an insulator, has a slightly weaker performance than other insulators. Instead, it is made from natural ingredients. Jute can be cultivated in hot and humid climates, including Iran, and even in areas with low fertility and without pesticides and chemical fertilizers. Jute has global consumption, high production potential and diverse uses, and ranks second among plant fibers after flax. The binder of this biocomposite, i.e. silicone sericin, is also completely natural, and the use of sericin in the silkworm cocoon industry will bring economic and environmental benefits. Therefore, the biocomposite of jute-sericin non-woven fibers is a light material, resistant to moisture and heat, and has good strength against incoming loads. It is part of green materials and is economically suitable for production and use, and further study on these composites will be an important step in achieving environmental sustainability and reducing energy consumption due to their importance.

Conclusions
It is essential to use durable and light materials with suitable physical and mechanical properties and compatible with the environment in construction and architecture. The aim of this research is to present a proposed model for the production of fiber non-woven composite panels. Therefore, by using renewable natural raw materials such as natural fibers and using silkworm cocoons and sericin in it, the production of non-woven biocomposite was achieved, which is environmentally friendly and cost-effective and has good performance against heat and humidity. One of the applications of this composite is thermal insulation, because the appropriate thermal performance of this composite is accompanied by favorable biological and economic benefits. After proposing the model of this composite, its thermal behavior in the external shell of the building was investigated. The results show that if this insulation is used between the external facade and the internal wall, the thermal behavior of the building will be 12.7% better than if it is not used. The behavior of this biocomposite against moisture and heat transfer makes it possible to use it as a new construction material in the direction of sustainable architecture.  Abstract Nowadays, the relationship between bio mimicry science and various fields including extended architecture and the study of patterns, systems, and biological elements, is a way to create solutions to the problems of human life. Silkworm cocoon is a biological structure and a natural composite that has evolved during the time and is a good response to environmental conditions for silkworm and has high physical and mechanical properties against stress and has a good function as an insulator against ambient temperature conditions. Understanding the structure relationships of silkworm cocoons inspires how to create composite structures, including non-woven, lightweight, and high-strength composites.

References
In this study, the descriptive-analytical method and logical reasoning method attempt to introduce the structure of silk cocoon, using sericin cocoon and natural fibers, which for various reasons such as lightness, non-pollution, abundance, and low-cost, can be a suitable alternative to artificial fibers, offer materials as a non-woven bio composite. These materials, which have recyclable properties and are suitable in terms of energy consumption, can be used as moisture and heat insulation. This performance was simulated and analyzed in the outer shell of the building and using the Hani Bee energy analysis plugin in the Grasshopper for the hot and dry climate of Kashan. The results show that the proposed non-woven composite of natural fibers can help to improve the thermal performance and reduce the heat