**5. Usage of recycled polymeric materials in denim**

Denim itself is very well-known for its durability and long-lasting properties. Although there is no certain lifetime for a jean, the common belief is that it lasts longer than any other garment. This belief relies on the fact that Jeans used to be the uniform of the miners during Gold Rush in the United States.

The fabric parameter that indicates the durability is the strength value of the fabric. Strength value is derived from both yarn strength and the construction. Since the construction remains the same for denim fabric, yarn strength should be analyzed to better understand the contribution of recycled fiber to the strength of the yarn. Fiber fineness (dtex), staple length (mm) and tenacity of the fiber (cN/ Tex) are the most important parameters that contributes to the yarn strength. Fiber fineness directly determines the number of fibers in the cross-section of the yarn. The finer the fiber, the number of fibers contributing to the strength will increase and the yarn strength will be higher. Staple length refers to the average length of individual fibers. The shorter the staple length, the more difficult it can be to spin. More twist is needed if the staple length is short. Therefore, this parameter plays an important role on spinnability and strength of the yarn. Tenacity of the fiber directly relates to the yarn strength. The stronger the fiber, the stronger the yarn will be.

Mechanical recycling of natural fibers, mainly cotton, shortens the fiber length drastically. Therefore, a perfect mix of pre & post consumer recycled materials and alternative natural materials is essential. Chemical recycling overcomes this challenge since the required fiber length can be set in the process and the tenacity of recycled fibers are almost the same with the virgin versions in most of the cases. Hence, this ability creates a longer lifetime for a recycled denim with recycled polymeric materials. As seen in **Table 3**, PET and Recycled PET have the highest tenacity values in comparison to the Cotton, Tencel, Recycled Tencel and PLA. This means that using PET in denim increases its durability hence lifetime. On the


#### **Table 3.**

*A comparison of physical properties of selected fibers [84–87].*

other hand, both Tencel/Refibra and PLA have higher tenacity values than Cotton. In theory, using chemically recycled polymeric material and biologically produced PLA in denim production increases the lifetime of the jean.

However, the environmental impact of petrolueum based fibers are fairly high. Synthetic polymers, PET in this study, are produced from fossil fuels. The environmental concerns regarding the use of synthetic polymers bring the main discussion in this study: The environmental impact of recycled polymeric materials and biobased materials in denim production.

In the previous study of the authors, the effect of using regular, organic and recycled cotton in a denim fabric on environment was analyzed [88]. As a continuum, this chapter analyzes the environmental impact of using polymeric and recycled polymeric fibers in denim fabrics. The past 5 years witnessed the commercialisation of recycled versions of elastane, Tencel®, T400® and many novel bio-based plastics, such as PLA, starch plastics. Today, main recycled polymeric materials that are used in denim production are as follows:


In order to eliminate the effect of finishing processes on the lifecycle assesments of the fabrics, Recycled Elastane and Recycled Bio-based Polyester are excluded in this study. Instead, recycled bio-based polymer, Poly Lactic Acid (PLA) fiber is included. In this study, six fiber compositions for the same denim construction (**Table 4**) are determined to calculate and analyze the effect of different recycled polymeric materials in denim.


**Table 4.** *Article specification.* *An Evaluation of Recycled Polymeric Materials Usage in Denim with Lifecycle Assesment… DOI: http://dx.doi.org/10.5772/intechopen.99446*


#### **Table 5.**

*Summary of raw material data used in this Study.*

PET, recycled PET and PLA fibers are supplied from Reliance, Unifi and Trevira, respectively. Tencel & Refibra are lyocell fibers produced by Lenzing AG. More than 99% of wood and dissolving wood pulp used by the Lenzing Group is either certified by FSC® and PEFC™ or inspected in line with these standards. The trees grow quickly without the use of pesticides, fertilizers, irrigation or GMO. Tencel with Refibra Technology contains 30% recycled material as pre-consumer cotton scraps and post-consumer garments from the textile value chain as raw materials and produced with Tencel technology [89].

**Table 5** below presents the raw material data set used in the calculation of lifecycle assesment values of the articles listed above.
