Recycling of technical textiles

Excerpt: TIFAC-CORE in Technical Textiles, DKTE, Society's Textile & Engineering Institute, Rajwada, Ichalkaranji - 416115, Dist: Kolhapur, Maharashtra

P V Kadole, N. B. Timble , Rajanna L Gotipamul & Namitha R Jhadav

TIFAC-CORE in Technical Textiles, DKTE, Society's Textile & Engineering Institute, Rajwada, Ichalkaranji - 416115, Dist: Kolhapur, Maharashtra

Introduction

RECYCLING involves the collection of used and discarded materials, processing these materials and making them into new products. It reduces the amount of waste that is thrown into the community dustbins thereby making the environment cleaner and the air more fresh to breathe. Surveys carried out by Government and non-government agencies in the country have all recognized the importance of recycling wastes. However, the methodology for safe recycling of waste has not been standardized. Studies have revealed that 7 %-15% of the waste is recycled. If recycling is done in a proper manner, it will solve the problems of waste or garbage. At the community level, a large number of NGOs (Non Governmental Organizations) and private sector enterprises have taken an initiative in segregation and recycling of waste (EXNORA International in Chennai recycles a large part of the waste that is collected). It is being used for composting, making pellets to be used in gasifiers, etc. Plastics are sold to the factories that reuse them. The steps involved in the process prior to recycling include Collection of waste from doorsteps, commercial places, etc., Collection of waste from community dumps. & Collection/picking up of waste from final disposal sites.

Recycled Cycle

Most of the garbage generated in the household can be recycled and reused. Waste recycling has some significant advantages. It leads to less utilization of raw materials, reduces environmental impacts arising from waste treatment and disposal, makes the surroundings cleaner and healthier, saves on landfill space, saves money & reduces the amount of energy required to manufacture new products. In fact recycling can prevent the creation of waste at the source. Recycled textiles are used in various products as shown in Table 1. These products range from very technically sophisticated items used in automobiles and aircraft to very mundane items such as a flower pot.

Textile waste industry operations

Traditional textile wastes can be in fiber, thread or in fabric form. Textile waste may include card waste, motes, thread waste,selvages, substandard fibers and fabrics, filament and tow waste. There are two main processes for recycling waste: tearing process and cleaning process.

Tearing Process

The tearing process consists of the following:

  • Grade incoming material
  • Collect together mixes to ensure proper consistency
  • Prepare the mix for feeding on to a conveyor
  • Blend the material while feeding the conveyor
  • Sort out trash, also while feeding
  • Cut the material to manageable size, typically 2 inch to 6 inch
  • Tear the material with tearing machine to return it to opened fiber form
  • Bale the end product

In this way polyester/cotton threads are machined into open fiber. These fibers can be used for stuffing and for some industrial applications such as filter and caskets. In general, these fibers may be spun into very coarse count yarns such as mop yarns (a mop cord is made of four to eight plied yarns). Friction spinning is suitable for this process. Polyester filaments are cut and open end so that the end product can be used as polyester stuffing. Carpet waste can be opened up so that it may be used to produce carpet underlay. Apparel cuttings are processed into the raw materials for sound deadening the pads used in automobiles. Cotton threads are opened to fibers and are used in the absorbent cotton industry. Recycled absorbent pads are used for oil drips and spills, walkways, packaging and cushioning. Mattress and furniture insulator pads are also made from recycled fibers. Knobs are mixed with staple fibers to produce novelty yarns.

Cleaning process

The cleaning process handles the cleaning of soft cotton or polyester/cotton card waste and gin motes. The raw materials are blended and processed through step cleaners and lint cleaner using equipment similar to that used in cotton gins. Through this process, card waste can be cleaned up until it can be substituted for a low grade of cotton usable in mop yarns and other coarse count yarns. Gin motes are handled in the same way. The mote waste, the byproduct of cotton waste cleaning operation, has been used in farming fields by mixing with the soil. Compost made of recycling waste is an excellent fertilizer with good carbon and nitrogen components. Lehner list the major challenges in recycling textile and fiber products as follows:

  • Poorly segregated by-product: this occurs when different types of wastes are collected and mixed together in a way that reduces the overall value of the waste.
  • Contaminated by-products: when possible, textile waste should not be mixed with other waste such as metal, wood or cardboard.
  • Poorly packaged material: poorly packaged fiber materials in bad bags increase the cost of handling and storage.

Recycling of industrial textiles

Recyclability Potential Index (RPI) of Textile fibres

A focus on recycling is one of the key pillars in this environmentally conscious era. In recent times, the situation is forcing people to recycle everything that is produced due to various factors such as present and future projections of scarcity of potential resources, limited landfill space, governmental policies, rewards in terms of monetary benefits given to people when they return the product for recycling. Textile products, occupying a significant proportion of one's daily activities in almost every place, need to be recycled. Many types of fibres are being used to manufacture textile products for daily use and they necessarily need to be recycled at the end of their lives. The potential recyclability of different fibres varies from one fibre to another and many factors play a major role in deciding their recyclability. This study proposes a concept for the Recyclability Potential Index (RPI) of textile fibres considering their environmental and economic gains from the recycling process and also attempts to quantify the Recyclability Potential Index (RPI) of ten common, widely used textile fibres. According to the developed system, polyester and polypropylene seem to be bestowed with higher and the nylon 66 appears to have the lowest RPI.

Reduce. Reuse. Recycle. These three words have become synonymous with the Green Movement

Processing of waste

High efficiency textile/cloth waste recycling machine

Fibres for Recycling

Polyester Fiber Specs

  • 1.2 & 1.5 D: semi-dull and optically brightened fibers, customized for optimum spun lace performance & value
  • 1.2, 1.5, 6 & 9 D: semi-dull and optically brightened fiber, created for enhanced performance in chemical bond applications
  • 1.2, 1.5, 3, 6 & 9 D: semi-dull and optically brightened fiber, designed for excellent performance in needle punch end uses
  • 1.0, 1.2, & 2.25 D: super white copolymer fiber, with enhanced moisture management capability

http://www.atlas-mts.com/Plastic nonwoven production by thermal bonding using heated calendars

When synthetic fibres and/or polymers are heated they become soft and tacky. On cooling, fibres that are in contact with each other fuse together as the polymer solidifies. This advantageous use of thermoplastic behavior forms the basis of thermal bonding. In order to achieve the desired fusion, heat or heat and pressure are applied under strictly controlled conditions. Fibres, which enable thermal fusion can be processed in 100% form or in mixtures with high-melt thermoplastic fibres out of textile mill waste and plastic mill wastes. During this investigation, calendar bonded ECFY' out of POP mill waste nonwoven related products containing 0%, 25%, 50%, 75%, and 100% synthetic fibres and/or polymers were produced successfully in weights ranging from 400 - 1000 g. All the physical properties of these plastic nonwovens are greatly influenced by the nature of synthetic fibre used (POP, LDPET, LLDPET, and PET), and also by bonding pattern and conditions (50, 75, and 100 kg! cm and 100, 150, 200°C). In general, plastic nonwoven samples are denser, more compact, less permeable, and less extensible, less resistant to bursting than all the other technical nonwovens. They also exhibit good overall strength in both directions. The method and material used in the bonding process substantially influences the appearance and ultimate functional properties of resulting nonwovens. The web is then passed between heated calendar rollers to promote partial melting and joining of ECFY at crossover points. The process involves three physical factors -- bonding pressure, bonding temperature and bonding time.

Recycling of industrial textiles is more difficult than traditional consumer textiles because they are built as durable, high performance products. For example, coatings are designed to adhere inseparably to their substrates. Laminations adhesives are supposed to have long-term bonding properties. Therefore, engineered textile structures are difficult to disassemble and reuse. Most of the time, technical textiles can be a solution to environmental concerns. However, sometimes they may be the cause. For example, medical textiles, whether they are disposable or reusable, must ultimately be destroyed because they are often considered hazardous. Infectious medical waste is usually disposed of through incineration. Incineration is an effective way to eliminate the infectious medical waste while reducing the size of the waste material. However, incineration results in a byproduct of fly ash and emission that may cause health problems if not filtered.

Another example of the industrial textiles that may hurt and help the environment is the industrial filters. They are used to reduce pollution, which helps the environment. When they are replaced, they are disposed of in landfills or confined if they contain noxious or radioactive substances. This will diminish the landfills. Polymers can be classified as thermo set and thermoplastic. A thermoplastic material can be repeatedly heated to its softening point, shaped and then cooled to preserve the remolded shape. In a thermo set polymer the heating process cannot be repeated due to charging and degradation. The reason for this behavior is the cross linking which does not exist in thermoplastic materials. Examples of thermoplastic materials are polyester, polyethylene, polypropylene; examples of thermo set nitrile and butyl. Technical textiles that are made of thermo set polymers cannot be remelted for recycling purposes.

Recycling technology

There are several techniques that can be used to recycle industrial products as discussed below. It should be noted that some of the recycling techniques mentioned in this paper may still be under development for textile applications. Some of the techniques have been used in other industries successfully and may be adapted to the textile industry.

Solvent extraction

Solvent extraction has been used for carpet recycling. In this process, a consecutive chain of solvent is used to remove polymers of interest. For example, acetone and hexane are used to remove oils; ethylene dichloride is used to dissolve and remove the ABS and PVC plastics; xylene is used to extract polypropylene and polyethylene. PVCs can be removed with the esters, ketones or chlorinated hydrocarbons. Nylons can be extracted with phenols.

Cryogenic fracture

In this method (with or without mechanical or ultrasonic vibration) the temperature of polymers is reduced to below glass transition temperature with liquid nitrogen or other cold temperature materials which makes the coating or film brittle. Polymers are then broken and separated. To increase separation efficiency, mechanical or ultra sonic vibrations are used.

Pyrolysis kiln

Pyrolysis is the thermal decomposition of organic material in an oxygen-deficient environment. The technique has been used for the production of fuels and chemicals from organic feedstocks such as waste tires. The thermal organic reactor uses molten lead in a sealed chamber to reduce the organic materials to their organic residues, without harmful emissions resulting from incomplete combustion. A conveyor and filter system separate and removes the residue, allowing a continual feed process.

Powdering (Solid-state shear extrusion)

This method being developed at the Illinois institute of technology uses high pressure at low temperature to grind the material for further processing.

Other recycling technologies

Potential future method for recycling technology includes hydrolysis to monomers, alcoholysis to monomers, catalysis and biological separation. Hydrolysis and alcoholysis are chemical processes used to reduce polymers to their constituent monomers. Catalysis uses additives or accelerating agent that do not get used up during the chemical reaction.

Biological organisms can break down certain synthetic chemicals. Other longer term potential methods may include thermal processing, microwave heating, surface heating, gamma irradiation, ice blast, and remanufacturing. In thermal processing, heat is applied to melt the polymers into their constituent parts. Infrared heating of the fabric surfaces (surface heating) to loosen the coating or adhesives may prove effective. Gamma irradiation (non-ionizing radiation) may induce favorable chnges in the structure of some coated and laminated fabrics. It is known that some types of irritation increase cross linking in certain polymers. Ice blast is a lowimpact surface scrubbing process that uses phase changes in rapidly melting ice. When small particles, fed from a nozzle at high speed, hit the surface, they melt and transfer energy to the surfaces. When the surface coating rebounds, it explodes outward and the surface is gently cleaned.

Recycling of multi-component structures

Industrial textile end products are quite often multicomponent structures. Typical products include tarpaulin, container curtain materials, conveyor belting, foam laminated textiles, membranes, decorative textiles on rigid moldings, nonwoven products and flocked substrates. For example textiles composites are made of reinforcement fibers and matrix materials. Nylon yarns are inserted in the filling direction in polyester paper making fabrics for abrasion resistance. A film with excellent chemical resistance is laminated to a substrate having good dimensional stability, but allows liquid penetration. This pairing usually required that different polymers are used for substrate and top layer. The more components are contained in a textile product, the more difficult it is to recycle it. The success of a recycling process depends on two criteria:

  • Reduction of material verity: fewer fiber materials finishing agents in a textile product make it easier to separate the individual components from each other and recycle them in a good quality process.
  • Reversible manufacturing processes: it is important that manufacturing processes, such as joining and bonding, are reversible for successful recycling.

Some of the current and possible future recycling methods for multi-component textile products were reviewed by Ehrlen et al. They summarize the major steps in recycling of multi-component textile products as follows:

  • Separation: separation or splitting is the treatment by which a bond between two or more materials is removed. During the separation process, the component should not be destroyed. Mechanical and chemical processes are possible.
  • Insulation/fractionation: following the separation is isolated or fractionated. Criteria influencing isolation include source material, size and specific gravity.
  • Reclamation - Material reclamation (mechanical processing, meltdown) - Chemical reclamation (alcoholysis, etc.) - "return to root" reclamation (hydrogenation, gasification)
  • Heat recovery

In mechanical separation, the interface of the textile composite is overstressed and destroyed by mechanical forces (tensile, shear, bending, impact, compression-decompression and torsion) a pretreatment process can be applied before the release process to facilitate the separation. Pretreatment technique can be low temperature treatment (inducing temporary brittleness), high temperature treatment (reducing adhesion), steam infusion and swelling of one of the components. Ehrler et al. suggested the following techniques. For sheet materials (larger than 0.3m²)

Examples of industrial textile recycling

Coated and laminated fabrics

Manufacturers of coated and laminated fabrics are interested in recycling and reclaiming of fabric scrap which is known as "edge trim" edge trim consist of cut selvedge ends, roll ends, reject lots, setup yardage and other waste materials. Disposal of this material is costly. In 1993, the total of coated and laminated fabric scrap was 6,187 tons. At an average East coast landfill tipping cost of $35 per ton the cost of this problem to the industry is almost a quarter million dollars per year. An example of this is the fabric used for the Denver International Airport roof where a good deal of fabric scrap was produced. There is a need of edge trim recycling especially for vinyl coated and vinyl laminated fabrics. The disassembly of laminated back into pure components is a reversal of the manufacturing process itself. The adhesive must be dissolved without destroying the textile component.

Carpets :

Discarded vinyl-backed carpeting is used to produce a broad range of usable products such as park benches, birdhouses and picnic tables.

Fabric from PET Soda Bottles

Recently work has been done to use post-consumer PET (polyethylene terephthalate) soda bottles to make fibers and fabrics. It was reported that fleece fabrics and geotextiles have been successfully made from PET soda bottles.

Nonwovens

A considerable amount of reclaimed fibers is used in nonwovens. Recycled nonwoven products range from middle and lower grade to functional and industrial grades. The variation in type, fineness, length and color of recycled fibers may cause high variability in the properties of the finished product. The principal parameters affecting the processing or reclaimed fibers in nonwovens are:

  • The degree of opening which is characterized by the percentages of fiber material and content of yarn and fabric remainders
  • The fiber length which is characterized by average fiber length and the percentage content fibers shorter than 5mm

Reclaimed fibers are increasingly used in needle geotextiles for separation and protective applications as well as hydraulic function involving filtration and drainage.

Recycling of technical textiles

(Contd. from pge 87)

Textile structural composites

As the use of composites spreads into more areas, recycling of composite materials is becoming economically viable and ecologically required. In the case of thermosetting composites, recycling is difficult. At best, thermo sets can be reused as filler materials in limited quantities. Conditions for recycling are more favorable in the case of thermoplastic materials. This is an advantage for thermoplastic composites to increase their market share.

Carbon fiber waste from cutting of reinforcing fabric during manufacture of composites can be reused to make chopped fiber or nonwoven composites. Carbon fiber is brittle and difficult to recover from a fabric with substantial reduction in fiber length. The degradation of the fiber length generally renders the fiber unsuitable for dispersion back into the original product. The brittleness also limits the kinds of textile processing that can be used. The manufacture of nonwovens requires only that the fiber be opened, and does not require the drafting and spinning steps, both of which are mechanically strenuous on the fiber. Mixtures of waste, high modulus, thermally stable materials (lick carbon) with thermoplastics waste (like polypropylene carpet backing) in a nonwoven structure might be heated and compressed to make relatively flat, moderate performance, fiber reinforce plastic panels.

The Deutsche Forschungsanstalt fur Luft and Raunfahrt (DLR) of Germany has recently introduced biodegradable construction materials called biocomposites that can be recycled as well. It was reported that the material can be used in many cases where glass fiber reinforced plastics have been used in the past. The biocomposites developed by DLR are based on natural fibers ( hemp, flax or ramie) and biodegradable matrix material. The matrix material can be polyester, modified cellulose, starches and starch containing products. It was reported that ramie or fax products adhesives 50% of the rigidity of glass fiber reinforced plastics, and hemp materials as much as 100%.

References

  1. Handbook of Industrial Textiles, Sabit Adanur
  2. Nonwovens from Recycled fibres, Asian Textile Journal,March 2014
  3. www.indiantextilejournal.com, Published August, 2011,
  4. www.sciencedirect.com/science/article
  5. www.fibre2fashion.com
  6. http://www.polyfibre.com
  7. www.stfi.de