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Production of FR textile
In the production phase of the FR cotton textiles during the finishing formulations, crosslinking agents are added to improve the flame retardancy and durability of the finish by developing a phosphorus-nitrogen synergistic effect (Uddin, 2013). The crosslinking agents for cotton are normally formaldehyde based, such as trimethylol melamine TMM and dimethylolurea (DMU) (Uddin, 2013). The treated cotton fabrics withstand a great number of launderings, dry cleanings or other cleaning procedures (van der Veen and de Boer, 2012). However, this finishing formulation is associated with the formaldehyde release (Bischof-Vukušić and Katović, 2012).
There is a big debate on the environmental impacts related to the use of the organophosphorus MPDA product as there is a high level of release of formaldehyde when MDPA and TMM are combined (Mohsin et al., 2013). The release of formaldehyde from treated fabrics can cause mild to serious human health problems such as headaches, irritation of eyes or nose and skin rashes.
Most importantly, it has been classified as a cancer-causing substance (a human carcinogen) (Fowler et al., 1992; WHO, 2006). Indeed, researchers have tried to modify or develop new crosslinking reagents, such as low formaldehyde-content reagents or reagents with no formaldehyde in their structures. The modified dimethylol dihydroxy ethylene urea (m- DMDHEU) and the dimethylol dihydroxy ethylene urea (DMDHEU) reagents are widely used in the textile industry. Normally, these low formaldehyde-content reagents are compounds containing N-methylol group and yet the N-methylol compounds can release formaldehyde eventually. In the finishing process of FR to cotton fabrics, the N-methylol can react with hydroxyl groups of cellulose or with reactive N-H groups. These reactions end up in an undesirable loss of crosslinking reagents, and eventually from the N-methylol compounds, formaldehyde is released (tovarna ZVEZDA, 2002).
In literature, some formaldehyde alternative reagents such as a butane tetra carboxylic acid (BTCA) have been proposed. This is however, more expensive than formaldehyde reagents, has a limited laundry efficiency, and decreases the mechanical attributes of cotton fabric (Paul, 2014). Indeed, sodium hypophosphite (SHP) was found to be a more effective catalyst for cotton fabric when used with polycarboxylic acids (Clark and Andrewes, 1989).
At the present time, formaldehyde is yet preferably used in commercially available FR formulations, as it is cheap and extremely effective crosslinking reagent for cotton fabrics.
Consequently, to cope with the impacts of formaldehyde on humans and the environment, there is a need to develop a formaldehyde-free formulation of finishes for cotton fabrics. Recent studies have brought some environment-friendly finishes for cotton fabrics, such as Chitosan phosphate (El-Shafei et al., 2015), enzymatic treatment (Wang et al., 2012), glycerol (Ferrero and Periolatto, 2012), α-hydroxycarbonyls (Meksi et al., 2012) and citric acid (Mohsin et al., 2013).
These environment-friendly finishes for cotton fabrics can solve the formaldehyde release problem; however, it requires a long set of experiments to achieve the desired results with limited information, particularly in formulations having numerous reagents or in the synergistic interactions. To overcome this problem, a formaldehyde-free crosslinking agent was used with the help of statistical tool to attain the optimized fixation to the cotton fabric. A FR formulation with formaldehyde-free crosslinking agents, such as citric acid, sodium hypophosphite and phosphoric acid was utilized (Paper VI). However, to consider the real-case-scenario, the commercially available FR formulation having formaldehyde as a crosslinking agent was considered for the main research.
Optimization of FR fixation with statistical tools
Optimization of formulations for the FR systems for textiles can be attained by statistically designed experiments with several reagents additives within specific boundaries (Antia et al., 1982; Cullis et al., 1991). A statistical experimental design system can be used to optimize the performance of cotton fabrics treated with the FR reagents by predicting an effective concentration of finish fixation with minimum loss in mechanical properties. The commercially available FR and crosslinking agent (discussed in chapter 3, under section; FR product and additives) is permissible to get optimization information by using response surface methodology on reagent concentrations and mechanical properties of the cotton fabrics after the treatment.
Surface response methodology (Box-Behnken)
Response surface methodology is an empirical modelization technique devoted to the evaluation of the relationship to a set of controlled experimental factors and observed results (Annadurai and Sheeja, 1998). The methodology involves a model base knowledge achieved earlier; the data can be based on experimental outcomes or statistical knowledge.
Degradation and elimination via advanced oxidation process
Advanced oxidation processes are well known for their capacity to degrade and mineralize a wide range of organic compounds which are sometimes resistant to conventional biological oxidation. Many advanced oxidation processes, including Fenton (H2O2, Fe2+) and solar photoFenton processes (H2O2, Fe2+ and solar irradiation) have proved to be useful in the degradation and mineralization of various organic toxicants and wastes (Xu et al., 2007) such as aromatic hydrocarbons (phenols, substituted phenols, chlorinated hydrocarbons, polycyclic aromatic), nitrogenous compounds and amines (Casero et al., 1997), and complex molecules like pesticides, dyes, surfactants, pharmaceuticals, and mineral oils (Harimurti et al., 2010).
Organophosphorus pesticide compounds have also been reported to be degraded by Fenton or Fenton-like reactions (Badawy et al., 2006).
Advanced oxidation processes are generally based on the generating reactions of short-lived hydroxyl radicals (OH•) (Glaze et al., 1987), which are powerful oxidizing agents reacting with the majority of organic compounds by the second-order kinetics (Esplugas et al., 2002). Some other advanced oxidation processes use either hydrogen peroxide (H2O2) or ozone (O3) source to generate oxidizing radicals such as hydroxyl OH• and hydroperoxyl O2H•. The OH• can be produced in-situ by various advanced oxidation process systems, for instance, chemical, electrochemical and/or photochemical reactions. It has been proved that these radicals have extremely high oxidation potentials: the OH• has a 2.8 V oxidation potential at pH 3 (Burbano et al., 2005). The major reactions for the generation of oxidizing radicals may be represented as;
Fe2+ + H2O2→ Fe3+ + OH− + OH• (1)
Fe3+ + H2O2→ Fe2+ + H+ + HO2• (2)
In literature, it’s rare to find studies reported on the degradation of organophosphorus FR compounds using the advanced oxidation processes such as Fenton’s reagent, especially, in the domain of durable FR textiles. A part of this work, we proposed to study an in-situ degradation of organophosphorus FR MDPA from the cotton fabric in aqueous solution.
The degradation of MDPA in aqueous media can be monitored by measuring COD (chemical oxygen demand) of the reaction mixture over time. The degradation and mineralization from fabric were monitored by flame test and thermogravimetric analysis. In this study, we utilized an AOP for the removal of a durable organophosphorus FR from cotton fabrics, with a perspective of improving the energy yield of discarded FR cotton textiles during the combustion or possible re-usability.
FR waste valorization by gasification
Like all textiles, the FR textile products eventually become waste. Generally, such products are considered as municipal waste and are disposed-off via landfill or incineration. The incineration of FR textile products can generate various toxic compounds, including halogenated dioxins and furans depending on the FR species (John, 2013). The development of such compounds and their consequent release to the environment is due to incinerators operating conditions and its emission controls (Simonson, 2000). On the other hand, it would be interesting to see whether the FR textiles can be gasified or not, since FR resists the combustion.
Gasification is an intact breakdown of the biomass particles into a flammable gas, volatiles and ash in an encased reactor (gasifier) within the sight of any remotely provided oxidizing agent (air, O2, H2O, CO2, and so forth) (Kumar et al., 2009). Gasification is a transitional step amongst burning and pyrolysis, which is a two-stage endothermic process. Within the initial step, the unstable parts of the fuel are vaporized at temperatures beneath 600°C by an arrangement of complex reactions responses. No oxygen is required in this period of the procedure (Curti, 2015).
Carbon monoxide, carbon dioxide, hydrocarbon gases, hydrogen, tar and water vapor are integrated into the unstable vapors. The by-products of the procedure, such as char (settled carbon) and slag are not vaporized. In the second step, char is gasified through the reactions with oxygen, steam, and hydrogen. A portion of the unburned char is combusted to discharge the heat required for the endothermic gasification reactions (Mann and Spath, 1997).
During the gasification process, a material (normally biomass) is burned in the presence of controlled oxygen, which yields synthetic gases as gaseous fuel. The gas is processed to make different chemical products or biodiesel. Consequently, gasification is a major environmental approach to attain biomass energy. The gasification process is dependent on certain operating parameters including gasification temperature, flow rates, oxidizing agents, feed type, properties, and design of the gasifier (Kumar et al., 2009).
Primary gasification products are gas, char, and tar. Gasification products, their creation, and some byproducts are emphatically affected by the gasification parameters, temperature, heat rate and fuel qualities. Vaporous items formed amid the gasification might be further utilized for heating or power generation (Pandey et al., 2015). The produced combustible gas during the gasification can be cleaned and utilized for the synthesis of unique chemical products or for the heat generation and additionally electricity.
Gasification is one of a technology that can even convert waste (from municipal solid waste (MSW) to agriculture or edit buildups, similar to coconut shells, rice husks, straw, wood deposits, bagasse, and so forth.) to a valuable and quality source for energy (Pandey et al., 2015). When dealing with complex disposals, gasification gives an upside of isolating the harmful substances from the fuel gas preceding the combustion.
In literature, studies utilizing LCA for investigating the waste to energy processes, focusing on incineration as a specific treatment can be found. Some of the studies are, integrated waste management system (Arena et al., 2003), a comparison performances of landfilling or mechanical treatment before combustion of solid recovered fuel (Finnveden et al., 2005). It would be interesting to compare environmental performance of landfilling, incineration and also gasification of FR textiles at their end-of-life.
LCA and environmental terminologies
In general, LCA is an environmental set of measures for gathering and inspecting the inputs and outputs of materials and energy and the related environmental impacts directly accountable for a product or system’s whole life span. The LCA approach is described in four phases: (1) goal and scope definitions, (2) inventory analysis, (3) impact assessment, and (4) interpretation (Curran, 2006). A descriptive LCA framework can be seen in Figure 3. The LCA of any product, service or activity is mostly inventory-based, where raw materials, energy, and environmental emissions are distinguished later (Ison and Miller, 2000).
It should be noted that LCA analysis provides an enormous multidimensional set of input and output data that are difficult to interpret and comprehend. Additional precautions are generally recommended while relating input to output data in the LCA product system to avoid uncertainties in impact analysis (Hermann et al., 2007). Moreover, LCA in general is conducted on two competing processes, in which a comparative analysis highlights the environmental benefits and drawbacks of one process over the other (Mann and Spath, 1997). Similarly, for a better understanding of the end-of-life phase of FR textile, LCA with comparative analysis was chosen.
Table of contents :
CHAPTER 1 INTRODUCTION AND GENERAL CONSIDERATIONS
1.1 FLAME RETARDANTS IN TEXTILE INDUSTRY
1.2 FLAMMABILITY OF TEXTILES AND CONSUMER SAFETY
1.3 TOXICITY OF FLAME RETARDANTS AND SUSTAINABILITY
1.3.1 Environmental impacts of flame retardants
1.4 RESEARCH FRAMEWORK AND THESIS OUTLINE
1.4.1 Ecological issues and eco-designing of end-of-life phase
1.4.2 Degradation of flame retardant species
1.4.3 Energy valorization of FR textiles by gasification
1.4.4 Comprehensive LCA of the eco-design
1.5 CONCLUSIONS
CHAPTER 2 PRELIMINARY BIBLIOGRAPHY
2.1 THEORETICAL BACKGROUND OF FRS
2.2 TYPES AND APPLICATIONS OF FRS
2.3 PRODUCTION OF FR TEXTILE
2.3.1 Optimization of FR fixation with statistical tools
2.3.2 Surface response methodology (Box-Behnken)
2.4 DEGRADATION AND ELIMINATION VIA ADVANCED OXIDATION PROCESS
2.5 FR WASTE VALORIZATION BY GASIFICATION
2.6 LCA AND ENVIRONMENTAL TERMINOLOGIES
2.6.1 Components of LCA
2.6.2 Cradle-to-grave and Cradle-to-gate variants
2.7 FR TEXTILES AND ROLE OF LCA
CHAPTER 3 MATERIALS AND METHODS
3.1 FLAME RETARDANT PRODUCT AND ADDITIVES
3.2 PREPARATION OF FLAME RETARDANT TEXTILES
3.2.1 Pad-dry-cure process
3.2.1 Optimization of flame retardant finishing
3.2.2 Validation of optimized production parameters
3.3 DEGRADATION OF FLAME RETARDANT SPECIES
3.3.1 Degradation of flame retardant in aqueous form
3.3.2 In situ degradation of flame retardant on cotton fabric
3.4 CHARACTERIZATION METHODS FOR DEGRADATION
3.4.1 Consumption of oxygen for oxidation (COD)
3.4.2 Thermogravimetric analysis (TGA)
3.4.3 Pyrolysis combustion flow calorimeter (PCFC)
3.4.4 Mechanical properties
3.4.5 Flame test
3.5 GASIFICATION OF FR TEXTILE
3.5.1 Spouted bed gasifier
3.5.2 Preliminary pellet preparation
3.5.3 Gasification of flame retardant textiles after degradation
3.5.4 Temperature control in the rig
3.6 CHARACTERIZATION METHODS FOR GASIFICATION
3.6.1 Pellet flow rate and thermal transitory analysis
3.6.2 Syngas analysis
3.7 COMPREHENSIVE LCA OF FLAME RETARDANT TEXTILE
3.7.1 Functional unit and system boundaries
3.7.2 Life cycle inventory (LCI) and comparative analysis
3.7.3 End-of-life scenario building
3.7.4 Life cycle impact assessment
CHAPTER 4 DEGRADATION AND ELIMINATION
4.1 DEGRADATION OF FLAME RETARDANTS
4.1.1 Degradation of FR in aqueous form
4.1.2 In situ degradation of flame retardant on cotton fabric
4.2 CHARACTERIZATION RESULTS OF DEGRADATION
4.2.1 Flame test
4.2.2 COD reduction
4.2.3 Thermogravimetric analysis
4.2.4 Pyrolysis combustion flow calorimeter (PCFC)
4.2.5 Mechanical properties
4.3 GENERAL DISCUSSION
CHAPTER 5 THERMAL VALORIZATION BY GASIFICATION
5.1 THERMAL VALORIZATION OF TEXTILE PELLETS
5.1.1 Gasification of textile pellets
5.2 CHARACTERIZATION RESULTS OF GASIFICATION
5.2.1 Thermal transitory analysis
5.2.2 Gasification temperature
5.2.3 Analysis of gas evolution
5.3 GENERAL DISCUSSION
CHAPTER 6 VALIDATION BY LIFE CYCLE ASSESSMENT
6.1 LCA OF FLAME RETARDANT TEXTILES
6.1.1 Comparative inventory analysis
6.1.2 LCA results and comparative analysis
6.2 CHARACTERIZATION RESULTS OF END-OF-LIFE SCENARIOS
6.2.1 End-of-life analysis for landfill
6.2.2 End-of-life analysis for incineration
6.2.3 End-of-life analysis for gasification
6.3 GENERAL DISCUSSION
6.3.1 Recycling alternatives for FR textiles
CHAPTER 7 CONCLUSIONS AND PERSPECTIVES
7.1. CONCLUSIONS
7.2. REUSE AND RECYCLING OF FR TEXTILES
7.3. FUTURE PERSPECTIVES
REFERENCE
