A fundamental feature of the current economy is the linear growth in resource consumption. Materials typically go through 3 stages of manufacturing, use, and disposal. Companies extract raw materials and use energy and labor to make products that are then sold to end consumers. When these products no longer perform their inherent functions, consumers discard them. Although the development of science and technology has greatly improved production efficiency, it has also led to an unprecedented increase in the dependence on resource input in production. This dependence constrains economic development in many ways. Many businesses face the risk of unpredictable resource costs. Fluctuations in resource markets can sometimes erode a company’s profitability. As the global resource extraction continues to increase, natural resources are increasingly depleted, and a large amount of waste is also generated, which greatly affects the ecosystem. These problems will persist as the global population continues to grow. If we only rely on the improvement of production efficiency, we can only delay the coming of evil consequences. The development of circular economy has become an effective means to solve the above problems.
Compared with the traditional linear economy, the circular economy can effectively reduce the input of materials and the generation of waste. In circular mode, the produced products can be redesigned, reused and recycled. The circular economy requires closed-loop production, energy regeneration and systems thinking. Closed-loop production means that the surplus material in production can be used as raw material for other new products, ultimately drastically reducing the amount of material that goes to landfill. Ideally, all waste materials are turned into another raw material. Energy regeneration requires that the energy that feeds economic development comes from sustainable resources. Systems thinking refers to an economic system in which all participants are closely linked and operate as a whole.
The transition to a circular economy will disrupt the status quo: new opportunities and problems are on the horizon. Teijin Aramid is trying to address the problems encountered in the transition to a circular economy in the following ways.
——— improve recycling. End-of-life aramid fibers are collected and used as raw materials for the preparation of pulp.
——— improve the service life of aramid fibers. The new aramid fiber developed by it has better long-term mechanical properties under different load and temperature conditions.
——— develop new applications that accompany the emergence and growth of the circular economy. Currently, Teijin Aramid is working hard to find potential businesses, establish partnerships, and promote the use of the company’s aramid products in these areas. For example, aramid is used as a reinforcement material for hydrogen pipelines.
This article describes SINOARA aramid recycling in detail in the above three aspects.

recycle

The production process of aramid has been adjusted several times to reduce its ecological impact. One such success story is the production of pulp from recycled aramid, the recovery process of which is shown in Figure 1.

Not all aramid pulp is prepared using this process, and some high-purity pulp is made directly from pure aramid. The raw materials for the production of pulp are aramid waste from various end products: unidirectional non-woven cloth (UD cloth), residual yarn, reinforced fibers, vests and ropes, etc. These raw materials are first shredded and a variety of processes are used to reduce the contaminant content to obtain high-purity (>90%) aramid. Sometimes it is also possible to achieve the desired quality of recycled aramid products by adding a portion of high-purity aramid yarn. After grinding, the intermediate product is transformed from fibrous to pulp. Aramid pulp is often used as an alternative to asbestos for brake linings and gaskets.

2

Improve the long-term stability of aramid fibers

The contribution of aramid fibers to the circular economy is not only about recycling. If the service life of aramid fibers can be extended, that is, the service life of the end product can be improved, the energy demand and energy consumption per unit time will be effectively reduced.
Twaron and Technora are known for their high stability under long-term load. This property of aramid is important for its use as a reinforcing material for optical fibers, tires and mooring lines. Teijin Aramid has been working on the development of aramid with low creep rates. Figure 2 shows the creep rates of Twaron1000, Twaron2200 and TwaronD3200 at room temperature. The loads applied during the test are 30% and 50% of the fiber breaking strength (BS), respectively. During the creep test cycle lasting nearly 1A, none of the fibers broke. As shown in Figure 2, the new generation of Twaron fibers has a low creep rate. After about 1A, the creep rates of Twaron 1000, Twaron2200 and Twaron D3200 fibers were 0.27%, 0.14% and 0.07%, respectively.

Twaron 1000, Twaron2200 and Twaron D3200 fibers have logarithmic creep rates of 0.041%/dec, 0.020%/dec and 0.013%/dec, respectively.
The creep rate of Twaron is independent of the fiber load. For example, Twaron1000 and Twaron2200 have very similar creep rates at two different load levels (30% and 50% of breaking strength, respectively), while creep accelerates at most polymers at high loads.
Time to failure (tTTF) is an important indicator to evaluate the long-term stability of aramid. This indicator measures the long-term stability of aramid by measuring the time it takes for fiber to break under a certain load. The failure time tends to decrease as the load increases and the temperature increases. Figure 3 shows the change of tTTF of TechnoraT200 and liquid crystal polyester (LCP) at room temperature and high temperature (140 °C). The straight lines in Figure 3 show the fit of the experimental data. As can be seen from Figure 3, the stability of LCP yarns at room temperature is better than that of Technora T200. However, due to its good heat resistance, TechnoraT200 is more stable than LCP at high temperatures (140 °C).
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Based on the Eyring formula, Knoester et al. proposed a dynamic model to illustrate the relationship between tTTF and load and temperature, see Equation (2).

Equation (3) shows that the logarithmic value of the time to failure changes linearly with the change of applied stress (load), which is consistent with the fitting results for the time to failure in Figure 3. Parameter values for several specifications of Twaron can be obtained by consulting the references.

Figure 4 shows the modulus of storage of Twaron and LCP as a function of temperature. Dynamic mechanical testing (DMA) characterizes the viscoelastic behavior of materials at different temperatures. As can be seen from Figure 4, the decay of Twaron’s storage modulus at high temperatures is relatively slow compared to LCP fibers. LCP begins to melt at about 330 °C, as can be seen from the loss state of its storage modulus. Twaron can withstand higher temperatures. At an ambient temperature of 400 °C, the storage modulus of the Twaron fiber is still above 80 GPa until the ambient temperature reaches 500 °C, when the Twaron fiber begins to decompose.

3

Develop new applications to promote the circular economy

The transition to a circular economy offers many new business opportunities. Teijin Aramid is researching these new opportunities and is committed to promoting new applications of aramid products. A typical example is the use of VICWA fibers as reinforcements for hydrogen delivery thermoplastic pipes (RTPs). Compared to conventional metal pipes, VICWA RTP is lightweight, resistant to high pressures (about 30 MPa) and, more importantly, inert to hydrogen. In 2018, the German company Pipelife, a manufacturer of VICWA RTP, signed a 4.5km infrastructure project with the port of Groningen. According to Pipelife’s plan, construction began in June 2019.
Teijin Aramid is actively working on the transition to a circular economy. Its products VICWA, Twaron and Technora perform well under harsh load conditions. Teijin will work with its partners to actively seek and work to build a new future for the next generation.
References: Z.Y.Cao, O.Grabandt, Wang Hongqiu. Contribution of aramid fiber to circular economy[J].International Textile Herald,2020,48(08):20-21+48.)