Here in this review paper description is given about a type of polyamide fibre i.e. Nylon-66. The methods of preparation of monomers, polymerization, manufacturing methods of nylon-66, spinn…Full description
Proceso industrial de obtención de Nylon 66 aplicado a la industria
Material Scenario Undyed recycled nylon 6 woven textile. textile. General process for chemical depolymerization depolymerization of waste nylon 6 materials, primarily carpet, carpet, for secondary caprolactam and nylon 6 ﬁber production. Major unit processes include collection of post-consumer waste, sorting, shredding, depolymerization, distilling, melt-extrusion, yarn spinning and textile construction. construction. Data used in this report come from various sources and the scenario is not geographically speciﬁc.
Common Uses In Apparel And Footwear Due to the fact that recycled nylon 6 is produced from virgin quality caprolactam, it can share many of the same uses as virgin nylon. The manufacturers of EcoNyl have used recycled nylon from ﬁshing nets in apparel including socks, swimwear and underwear (Ditty, 2013).
Alternative Textiles Textiles That May Be Substituted For Material • Virgin nylon 6 • Virgin nylon 6,6 • Mechanically recycled nylon 6 • (Refer to virgin nylon 6 snapshot for other substitutes)
Life Cycle Description Functional Unit 1 kilogram of chemically recycled, undyed nylon 6 fabric
System Boundary Cradle to undyed woven fabric. The data presented within include all steps required to turn the postconsumer material into woven fabric, including transportation and energy inputs. Capital equipment, space conditioning, support personnel requirements, and miscellaneous materials comprising <1% by weight of net process inputs are excluded. excluded. Incineration of waste materials is not included in this study. study.
Allocation Cut-oﬀ approach. The “ﬁrst life” of the product (e.g. as carpet) is considered entirely separate from the “second life” life” (e.g. as a shirt), thus any environmental impacts of producing the waste material used to produce the recycled nylon are allocated entirely to the waste material.
A wide range of nylon waste is generated that can be collected, processed, and recycled into new nylon materials. A signiﬁcant barrier to eﬃcient collection and recycling is the diversity of nylon materials – e.g., nylon 6, nylon 6,6, nylon 6,10, nylon 11, nylon 12, etc. Nylon collection and recycling is most cost eﬃcient when there are large volumes of relatively homogenous waste material (e.g., carpet). Consequently, collection and recycling is mostly nylon 6 and nylon 6,6 waste carpet, with additional waste from virgin nylon production (Gupta and Kothari, 1997, p. 616), ﬁshing nets (Coplare, 2012), and textiles (pre- and post-consumer). None of these materials are collected via multi-material residential curbside collection programs. Rather, these materials are typically obtained through relationships with waste generators or takeback programs such as Interface’s ReEntry program (Interface, n.d., “Carpet to Carpet Recycling”). Processing
Alternative methods for recycling waste nylon materials and products include mechanical extraction (also called melt processing), and various methods of depolymerization followed by repolymerization (Wang, 2006, pp. 2-5). Processors typically choose a method that results in a speciﬁed level of output quality for a given waste nylon source. Relatively clean nylon can be depolymerized to provide inputs to polymerization of virgin quality nylon; conversely nylon with some contamination can be melt processed into lower quality nylon (Mihut et al., 2001, p. 1458). Mechanical processing1 involves cleaning the collected raw recyclate, shredding it into small pieces, densifying the shredded material to increase uniformity, melting the material and extruding the melted material to either form pellets or ﬁlaments. Pellets are packaged and shipped to customers that use mechanical means such as injection molding or extrusion to form a wide variety of nylon products. Filaments are formed (whether directly from shredded nylon or from pellets) by extruding the melt through a spinnerette and drawing, twisting, and winding the resulting ﬁbers that can then be processed further into yarn (EOS, n.d. “Recycling Nylon Carpet–Melt Processing”). Carpets that are shredded and melted without segregating the nylon from the backing material generally require a variety of additives to enhance compatibility of the mixed polymers. Even when segregated, mechanically recycled nylon generally results in a reduction in functional and performance properties (Lozano-González, et al., 2000). Nylon 6,6 is often mechanically recycled, whereas nylon 6 is commonly chemically recycled and can easily be processed back into the same products from which the original recovered nylon originated (Zeftron, n.d., “Reclamation & Recycling”). Due to its relatively high value compared with other polymers and because it easily oxidizes in storage resulting in gels when melt processed (Datye, 1991, p. 47), nylon 6 is a good candidate for chemical recycling via depolymerization (Wang, 2006, p. 2, EOS, n.d., “Nylon Carpet Recycling– Depolymerization”). Similar to mechanical recycling, carpets go through a process of sorting to determine polymer type, shredding, and separation using density techniques of the face ﬁber (the nylon 6) from the backing (synthetic polymers and/or bio-based materials) (Lu, 2010, pp. 38-39). The separated nylon 6 is then batch processed in a depolymerization reactor. The reactor is maintained as a nitrogen-free environment, while the nylon 6 is treated with superheated steam (Wang, 2010, p. 139) at elevated pressure (410-450 kPa) and temperature (250-340oC) (Braun, et al., 1999, pp. 471; 476; Dmitrieva, 1986, p. 231) to produce an aqueous solution of 10-50% caprolactam (Gupta and Kothari, 1997, pp. 617-618). Catalysts such as an alkali (sodium hydroxide), metallic sodium, metal oxides, or phosphoric acid and its salts are used to increase caprolactam yields, although they result in diﬀering levels of purity (Gupta and Kothari, 1997, pp. 617-618; Dmitrieva, 1986, p. 230). The aqueous solution of caprolactam can be contaminated with additives used in the original product, such as dyes, lubricant preparations and various ﬁllers (Dmitrieva, 1986, p. 234). To remove impurities, the recovered caprolactam may be distilled in the presence of an aqueous alkali at a temperature of 100-150oC (Dmitrieva, 1986, p. 238). 1
Mechanical processing generally includes a melting process and the terms are used interchangeably.
Alternatively, impurities may be removed via other methods such as solvent extraction, membrane separation, adsorbants, or oxidizing agents (Gupta and Kothari, pp. 49-50). The resulting pure caprolactam is repolymerized into nylon 6 in the same fashion as virgin nylon 6 (see the Nylon 6 Material Snapshot). Whether following directly from polymerization or from melting of pellets, the resulting nylon 6 is extruded through a spinneret typically comprised of 0.1-0.4mm diameter holes (Mather & Wardman, 2011). The emerging ﬁlaments are then extended in jets once they emerge from the spinneret, solidiﬁed with water in a quench zone, heated in a steam conditioning process, and treated with a spin ﬁnish before they are wound up (Bunsell, 2009 pp. 201-202). The ﬁbers are drawn to extend their length, orient the polymer molecules, and improve crystallization to obtain desired properties. While the ﬁbers may be drawn to between 200%-500% of the original length, the higher draw ratios are for technical industrial applications and the lower ratios (200-250%) are for apparel (Bunsell, 2009, p. 203). After drawing, ﬁlaments are subject to twisting, texturing, and heat setting to create the ﬁnal yarn. There are many levels of heat setting to increase the thermodynamic deﬁnition to the morphology throughout the yarn manufacturing process (Bunsell ,2009, p. 204). Finally, the yarn is then wound on spinning machines and ﬁnally re-wound on bobbins to create the ﬁnal product (Akovali, 2012, pp. 133-134). While nylon 6,6 can be depolymerized, it is not commercially viable due to the nylon 6,6 polymer being derived from two intermediate raw materials: adipic acid and hexamethylene diamine (HMDA) (see the Nylon 6,6 Material Snapshot). Lab depolymerization of nylon 6,6 by several routes has been demonstrated (Patil and Madhamshettiwar, 2014; Duch and Allgeier 2007), but has not been scaled to industrial operations. Textile/ Final Processes
Recycled nylon yarn which has been previously wound and spun can be woven into a variety of textiles.
Process Inputs Energy
Energy is necessary for collection of post-consumer waste (including transport, sorting, shredding, grinding, cleaning), processing (depolymerization, distilling, melt-extrusion, yarn spinning) and textile construction. Cradle to gate production of 1 kg of recycled nylon yarn requires 172 MJ2 (EcoNyl, 2011, p. 13). Depolymerization and repolymerization processes, ﬁlament production, and yarn spinning rather than waste collection and transportation are the major energy using processes (EcoNyl, 2011, p. 13). Weaving was identiﬁed by van der Velden, et al. (2014, p. 355) as having the highest impact for polymer ﬁbers when yarns are thin (<70 decitex); they calculated that weaving undyed greige textile (70 decitex) requires 229 MJ (van der Velden, 2014, pp. 351-352).3 Total cradle to gate recycled nylon energy is 401 MJ/kg. Water
Process water is used throughout the cradle to gate recycled nylon life cycle, particularly in cleaning the collected waste, steam treatment and post depolymerization puriﬁcation of caprolactam. Cradle to yarn water use is 84 L/kg. Of this total, collection is 18.5 L/kg recycled nylon yarn and processing is 65.5 L/kg recycled nylon yarn (EcoNyl, 2011, p. 13). Direct use of water weaving is minimal (unless water jet weaving is used). However, water use is embedded in electricity production (approximately 0.022 L/MJ) leading to an estimated 5 L of water per kg of woven textile for the 229 MJ/kg associated with weaving greige textile (Appendix Table B). 2 All reported EcoNyl inputs and outputs data are an average of two EcoNyl products, FDY Raw White and Textured Yarn Raw White (EcoNyl, 2011). 3 As nylon 6 recycling via depolymerization produces virgin quality product, weaving recycled nylon 6 is assumed to be equivalent to virgin nylon 6.
Chemical use in collection is limited with occasional use of detergents when cleaning post-consumer waste. Processing requires a range of chemicals depending on the particular depolymerization process method. Substances may include aqueous alkalis, sodium hydroxide, sulfuric acid, phosphoric acid, boric acid, metallic sodium, and metal oxides (Datye, 1991, p. 48; Dmitrieva, 1986, p. 232). Caprolactam puriﬁcation may be done with solvents such as toluene or other hydrocarbons. The chemistry necessary for polymerization is described in the Nylon 6 Material Snapshot. Additional substances used in yarn and weaving processes include spin ﬁnishes, coning oils, titanium oxide, antioxidants, and heat stabilizers (Datye 1991, p. 47). Physical
The primary inputs are post-consumer recycled products containing nylon such as carpets ﬁshnets, nylon textiles, and nylon production waste.
The use of post-consumer nylon products reduces the amount of landﬁll disposal of carpet and pollution of used ﬁshing nets in the ocean. Because the primary feedstock of the process is post-consumer material, the land required to produce recycled caprolactam is relatively low. Land use is limited to manufacturing facilities.
Process Outputs Co-products & By-products
After depolymerization, a pot residue is formed on the sides of the reactor, which contains caprolactam and the remains of the catalyst used (Dmitrieva, 1986, p. 232). Caprolactam can be extracted from the pot residue through distillation of water or sulfuric acid (Dmitrieva, 1986, p. 232). The ﬁltrate from this process can also be reapplied in the depolymerization stage of processing (Dmitrieva, 1986, p. 233). All unusable by-products produced from this process are typically burned in an incinerator and the resulting ash is utilized as a ﬁller in various plastic products (Mihut, 2001, p. 1,469). Solid Waste
During the sorting and shredding of input post-consumer products such as carpet, the face ﬁber (nylon 6 or 6,6) is separated from the backing, some of which may be recycled, while the remaining solid waste requires disposal (landﬁll or incineration for energy recovery). Nylon ﬁbers account for about half of the weight of the post-consumer carpet (Mihut, 2001, p. 1458). After depolymerization, a signiﬁcant amount of non-volatile waste and by-products remain in the reactor; where available, these are also incinerated for energy recovery (Mihut, 2001, p. 1,461). This waste can include titanium oxide, inorganic salts, tarry products of side reactions, antioxidants, stabilizers etc. (Datye, 1991, p. 48). Nonhazardous solid waste generation averaged 0.7 kg/kg of recycled nylon yarn (EcoNyl, 2011, p. 15). Weaving waste associated with electricity use is 0.9 kg/kg of woven textile. Cradle to gate recycled nylon textile waste is 1.6 kg/kg. Hazardous Waste/Toxicity
Hazardous waste generation for recycled nylon 6 yarn is approximately 0.2 kg/kg (EcoNyl, 2011, p. 15). These wastes include hazardous impurities removed from the materials in the depolymerization process as well as hazardous wastes generated in purifying caprolactam and repolymerization.
Toxic substances in the processing of recovered nylon 6 wastes include the chemicals used in depolymerization (aqueous alkalis, sodium hydroxide, sulfuric acid, phosphoric acid, boric acid, metallic sodium, and metal oxides, etc.) as well as the hydrocarbon solvents that may be used for caprolactam puriﬁcation (e.g., toluene) Wastewater
The production of 1 kg of recycled nylon yarn results in 0.005 kg PO43- eq. of eutrophication potential (substances that contribute to the exhaustion of oxygen in receiving waters) (EcoNyl, 2011, p. 14). Wastewater generated from the polymerization process or thermoplastic processing may be further puriﬁed to obtain pure caprolactam (Losier et al 1995). This wastewater contains 1-20% of solids of which 1-70% by weight is represented by caprolactam that can be catalytically cracked using aluminum oxide to obtain a more pure, concentrated caprolactam (Losier et al, 1995). Emissions
The collection and delivery of nylon waste to processors is a minor contributor to emissions EcoNyl, 2011, p. 14). Global warming potential is 7.8 kg CO 2 eq./kg recycled nylon yarn (EcoNyl, 2011, p. 14). Weaving is 10.7 kg CO2 eq./kg recycled nylon yarn. Cradle to gate recycled nylon textile is 18.6 kg CO 2 eq./kg (Appendix Table D). Table 1. Inputs And Outputs For 1 Kg Nylon 6 Cradle to recycled nylon yarn/ melt spun
Recycled nylon yarn to fabric/ undyed textile
Cradle to unﬁnished textile gate
GHG emissions (kg CO2 eq, 100 yr)
References i EcoNyl 2011, p. 13; 13; 14; 15 ii van der Velden et al., 2014, p. 351 Fig. 10 iii Calculations based on energy data from van der Velden et al (2014) and water values for electricity generation from Boustead, 2005, p. 7
Table 2. Comparison Of Inputs And Outputs For 1 Kilogram Nylon Cradle to Unﬁnished Textile Gate Recycled Nylon 6
Performance And Processing Functional Attributes And Performance
• • • • • •
Abrasion resistant 4 Excellent Tenacity 5 Low moisture absorbency 6 Durable 7 Elastic 8 Resistant to many chemicals 9 Table 3. Mechanical Attributes Of Recycled Nylon 6 Fiber Properties
Recycled Nylon 6 iii
Melting temp (oC)
Tensile Strain (%)
Tensile Strength (kg/cm�)
57 - 62 ii
Young’s Modulus (kg/cm�)
Water retention (%)
80 iv 1.6 iv
References i Akovali, 2010, pp. 123, 135 ii Kipp, 2004, Nylon 6 chart iii A review of the literature did not identify any data on the mechanical attributes of chemically recycled nylon 6 formulated for textile applications; data shown are for a chemically recycled nylon 6 for injection molding applications. iv BASF, 2015
The depolymerization process produces caprolactam, which when repolymerized, creates nylon 6 equivalent to virgin quality nylon (Mihut, 2001 p. 1460). Depending on the types of catalysts used in the depolymerization process, nylon ﬁbers may have lower ﬁber strength (Mihut, 2001, p. 1463). Processing Characteristics
When using chemical depolyermization, post-consumer feedstock can have any variation of molecular weight and chemical contamination without ruining the output caprolactam (Wang, 2010, p. 139). The caprolactam obtained through the depolymerization process is similar to virgin caprolactam in purity (Wang, 2010, p. 139). The quality of secondary caprolactam is improved when the temperature of depolymerization is reduced, however a reduction of temperature also lowers the yield of caprolactam from waste (Dmitrieva, 1986, p. 232). During the depolyermization process, the yield of pure usable caprolactam is a function of the catalyst concentration and the temperature (Dmitrieva, 1986, p. 230). For example, if sodium hydroxide (NaOH) is being utilized as the catalyst, a concentration of 1% can yield 90% pure caprolactam, where comparatively, a concentration of 15% NaOH will only yield 75% output caprolactam (Dmitrieva, 1986, p. 230). Similarly, the yield will increase as temperature increases from 230-250oC and decreases thereafter (Dmitrieva, 1986, p. 230). When using phosphoric acid as a catalyst, the yield of caprolactam is directly proportional to the amount of added catalyst (Dmitrieva, 1986, p. 231). Studies have shown that it is possible to obtain reproducible caprolactam yields from the depolymerization of shredded carpet of up to 85% (Elam et al., 1997, p. 994). 4 5 6 7 8 9
Akovali, 2012 p135 Ibid. Ibid. PlasticsEurope, 2014 p PlasticsEurope, 2014 p Akovali, 2012 p135
The quality of recycled caprolactam can also vary depending on the various additives used in the original consumer product. For example, if ferric ions are contained in the caprolactam, the ﬁber strength of resulting recycled nylon 6 will be reduced (Dmitrieva, 1986, p. 235). If impurities are well controlled, the recycled caprolactam can be polymerized into nylon 6 that can be reused for equivalent applications as virgin (USDOE, 2001). Aesthetics
The caprolactam obtained through the depolymerization process is similar to virgin caprolactam in purity (Wang, 2010, p. 139). Because of this, the majority of products produced from recycled nylon 6 have similar qualities to those produced with virgin nylon 6. In general, nylon 6 products have good retention of appearance and can be developed in a wide range of colors (Bunsell, 2009, p. 219). Its properties are similar to polyester, though it does wrinkle. The fabrics created from ﬁlament yarn are smooth, soft and lustrous (Hegde, 2004, section 9).
Potential Social And Ethical Concerns Recycling of nylon 6 avoids the use of benzene and other toxic chemicals required to produce virgin caprolactam. However, several chemicals in the recycling process are toxic, including the use of sodium hydroxide and sulfuric acid. There is a potential for spills or accidents associated with the use of these chemicals in processing plants.
Availability Of Material The rate of disposal of carpet ranges from 2-3 million tons per year in the U.S., and 4-6 million tons per year throughout the world (Wang, 2010, p. 137). Of this carpet, 60% is comprised of nylon ﬁbers that are available for recycling (Wang, 2010, p. 137). Carpet feedstock can be collected from landﬁlls, or by companies that collect post-consumer carpet directly following the consumer use phase. Interface has established a post-consumer nylon recycling organization that gathers postconsumer carpets and nylon ﬁshing nets to use in recycled nylon products (http://www.interface.com/ CA/en-CA/about?topic=Recycling). There is the potential for producing an estimated 34 million kg of post-consumer recycled nylon 6 annually according to Lu (2010, p. 69). Aquaﬁl is a supplier based in northern Italy with a depolymerization facility in Slovenia that produces 100% recycled nylon under the brand name EcoNyl (http://www.EcoNyl.com ). Around 50% of the recycled content in EcoNyl is from recycled post-consumer carpets and ﬁshing nets.
Availability Of Material Nylon speciﬁc recycling certiﬁcations do not exist. Scientiﬁc Certiﬁcation Systems has a recycled content certiﬁcation (http://scscertiﬁed.com/docs/SCS_STN_RecycledContent_V4-1_121809.pdf ) and the Textile Exchange Recycled Claim Standard is also available ( http://textileexch.wpengine.com/wpcontent/uploads/2016/01/TE-Recycled-Claim-Standard-v1.pdf ).
Cost Of Textile Reprocessed post-consumer nylon pellets cost around $0.40 per lb over a decade ago (Lave, et al 1998, p. 121). Currently, post-industrial nylon 6 pellets cost between $0.79-0.81 per pound (Resource Recycling, 2014, p. 1). Prices for recycled nylon tend to be lower or on par with virgin nylon and ﬂuctuate in conjunction with demand and imports (Resource Recycling, 2014, p. 1).
Questions To Ask When Sourcing This Material Q: Is the recycled nylon mechanically or chemically recycled? For chemically recycled nylon 6 material:
Q: How are by-products and wastes managed from the depolymerization and caprolactam puriﬁcation processes? Q: Is the nylon 6 polymerized from 100% recycled caprolactam? Q: Are ferric ions found in the post-consumer nylon product?
Appendix Calculations For Acrylic Table A. Energy For Recycled Nylon 6 Energy EcoNyl Yarn i
Cradle to yarn ii
FDY raw white (MJ)
Textured yarn raw white (MJ)
Weaving (70 dtex) iii
Cradle to Gate Undyed Textile Total
Notes/ References i All values related to EcoNyl yarn include carpet collection and grinding, depolymerization, re-polymerization, spinning, and texturizing/wrapping ii EcoNyl, 2011, p. 13 iv van der Velden, p. 351
Table B. Water For Recycled Nylon 6 Water
Cradle to yarn water use (average of EcoNyl yarns) i
Weaving energy ii
Water use per MJ factor from electricity production iii
Calculated water use
Cradle to Gate Undyed Textile Total
Cradle to yarn waste (average of EcoNyl yarns) i
Weaving energy ii
Waste per MJ factor from electricity production iii
Cradle to Gate Undyed Textile Total
Weaving water use
References i EcoNyl, 2011, p. 13 ii van der Velden, 2014, p. 351 iii Plastics Europe , 2005, p. 7
Table C. Waste For Recycled Nylon 6
Weaving waste use
References i EcoNyl, 2011, p. 15 ii van der Velden, 2014, p. 351 iii Plastics Europe , 2005, p. 7
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