Effect of wet processing operations on the functional properties imparted to polyester fabrics loaded with different metal oxides NPs part II: Effect of the different sequences of dyeing

The present work aims at investigating the effect of applying different dyeing sequences on the imparted functional properties to partially hydrolysed and bleached PET and PET/CO fabrics loaded with TiO2, ZnO and SnO2 nanoparticles (NPs). The so obtained dyed fabrics have been characterized using SEM, EDX and FT-IR analytical techniques. The obtained results revealed that, an interaction has taken place between COOH groups created on dyed polyester fabrics and each of the applied NPs. Moreover, the effect of loading and sequence of dyeing wet operation on the functional performances of polyester fabrics was evaluated by estimating its antimicrobial efficacy and ultraviolet protection properties. The antimicrobial activity was tested against B. mycoides, E. coli and C. albicans. It has been found that, loading polyester fabrics with TiO2 and ZnO during dyeing process using exhaustion or after dyeing using pad-dry-cure methods paves the way for imparting outstanding antimicrobial activity even after five washing cycles. Moreover, the obtained results have also reviled that, the UPF values are dependent on the sequences of the loading of abovementioed NPs during or after dyeing wet operation.


Introduction
In spite of the considerable properties of polyester fibres, which are superior in many ways to natural fibres, they also have some disadvantages (low hydrophilicity, not easily dyeable poor antistatic properties).
Most of these finishing methods depend on the activation of the surface of PET fabrics by creation of functional groups able to react with NPs. PET and PET/CO blended fabrics have been treated by Shalaby et al. 3,11 with TiO 2 and ZnO nanoparticles after surface activation of the fabrics by chemical and physical methods. It was found that, such activation facilitated imparting high antimicrobial and UV protection properties to the abovementioned fabrics.
It is important to emphasize that, the abovementioned properties were imparted to PET activated fabrics on libratory scale. At the same time technological and economic factors necessities carrying out such modifications on the wet processing operations line for fabrics. This can be achieved only after studying the effect of wet processing operations on the functional properties to PET and PET/CO blend fabrics loaded with different metal oxides nanoparticles.
Recently, Shalaby et al. 16 have investigate the effect of finishing on the properties imparted to bleached PET fabrics loaded with TiO 2 , ZnO and SnO 2 NPs. This study is a part of an going research project aimed at investigating the effect of wet processing operations on functional properties imparted to PET fabrics loaded with different metal oxides nanoparticles. It has been found that, loading fabrics with NPs during or after carrying out final finishing process leads to imparting outstanding antimicrobial activity. Moreover, the obtained results revealed that, the sequence of loading the applied NPs before or during or after carrying finishing wet operation highly affect the UPF values.
Based on the abovementioed the present article is the second part of the abovementioned research aims at investigating the affect of the different sequences of dyeing wet process on the functional properties imparted to PET and PET/Co blended fabrics loaded with TiO 2 , ZnO and SnO 2 nanoparticles.

Experimental
Materials PET (100%) and PET/CO blended (50/50) partially hydrolysed and bleached woven fabrics (PET→H→B and PET/ CO→H→B) were used throughout this study. PET and PET/CO fabrics were kindly supplied by local Egyptian textile companies. These fabrics were partially hydrolysed using the method described by Shalaby et al. 17 Its carboxylic content (10.9 and 22.4 meq/100 g fabrics) respectively were determined according to the method listed in Daul et al. 18 Chemicals • • TiO 2 , ZnO nano -emulsions and SnO 2 nano -powder (<100 nm) were purchased from Sigma-Aldrich.

Analysis
Carboxylic content. Carboxylic content was determined according to the method described by Daul et al. 18 Antimicrobial activity. Antimicrobial activity of PET→H→B and PET/CO→H→B fabrics loaded with metal oxides NPs was quantified using shake flask method. In this method the antimicrobial activity of immobilized antimicrobial agents is determined under dynamic contact conditions according to ASTM standard test method 2143 (2001).

Scan electron microscope (SEM). Fabrics morphology was characterized by scanning electron microscope (SEM) (JEOL Model TSM T20).
Energy dispersive X-ray (EDX). Energy Dispersive X-Ray (EDX) mode was applied for the elemental composition analysis. Gold layer was deposited on the samples before analysis.

Fourier transformation infrared (FT-IR).
The chemical structure was determined using the Fourier transformation infrared (FT-IR) spectrometer, model NEXUS 670, NICO-LET USA. The measurements were carried in the spectral range from 4000 to 500 cm −1 . Reflection percentage measurement technique was applied (R%). All investigated samples have the same area and weight.
Ultraviolet protection factor (UPF). Ultraviolet Protection Factor (UPF) was determined using UV-Shimadzy 3101 P C spectrophotometer. It is a double beam direct ratio measuring system. It consists of the photometer unit and a PC computer. UPF factor was determined according to the method described in Australian/New Zealand standard AS/ NZS 4399: 1996. UPF values were calculated automatically and classified according to Table 1.

Results and discussion
As we have mentioned before, the present study aims at clarification of the effect of wet processing operations on the valuable functional properties of PET fabrics gained after loading it with metal oxide nanoparticles. These studies will pave the way for the proper design of the technological process on the wet process line and therefore decrease the cost of modification. The effect of the sequences of loading with various types of NPs with dyeing wet process operation on the properties of bleached, partially hydrolysed and dyed polyester fabrics have been carried out as follows: 1. PET→H→B and PET/CO→H→B were separately immersed in TiO 2 , ZnO and SnO 2 NPs emulsion squeezed at 75% pick up increase, dried at 100°C for 60 min and cured at 150°C for 10 min. The loaded samples were then washed with distilled water to remove NPs that did not attach to the fabrics surfaces. The samples were dyed and evaluated (loading before dyeing).

Characterization of fabrics loaded with TiO 2 or ZnO or SnO 2 NPs and dyed at different conditions
Characterization of PET→B→H→D and PET/ CO→B→H→D Fabrics Loaded with TiO 2 , ZnO and SnO 2 NPs at different conditions. We have mentioned before that, the present work aims to clarify the effect of dyeing wet operation on the functional properties imparted to partially hydrolysed, bleached, dyed and loaded with different NPs polyester fabrics. Therefore, to confirm that the reaction has actually taken place between carboxylic groups formed on polyester fabrics and each of the used NPs, characterization of the so dyed fabrics seems to be of great importance. This was carried out through Energy Dispersive X-Ray (EDX), Scanning Electron Microscope (SEM) and FT-IR measurements.

Energy dispersive X-ray (EDX) and SEM
EDX and SEM analysis performed in EDX mode was used to confirm the presence of the applied TiO 2 , ZnO and SnO 2 NPs on the polyester fabrics, following the washing step, are shown in Figures 1 and 2. The obtained results confirm the existence of metallic Ti, Zn and Sn, irrespective of the mode and sequences of carrying out loading and dyeing operations. It was found that the fabrics still contain Ti, Zn and Sn even after five standard washing cycles (Tables 2  and 3). Data listed in Tables 2 and 3 also reveal higher Zn and Sn contents on PET→H→B→D and PET/ CO→H→B→D fabrics. Based on the abovementioned, one can conclude that the dyeing wet operation has no effect on the interaction between the COOH groups and the metal oxides NPs.
Scan Electron Microscope (SEM) The surface topography of PET→H→B→D and PET/CO→H→B→D fabrics loaded with metal oxides NPs and dyed was investigated using SEM technique. The obtained results (Figures 1 and  2) reveal the following: 1. PET→H→B→D and PET/CO→H→B→D fabrics are characterized by rough surfaces with pits ( Figures 1 and 2(a)).

Treatment of PET→H→B→D and PET/
CO→H→B→D fabrics with TiO 2 , ZnO, SnO 2 NPs emulsions using pad-dry-cure method after dyeing wet operation leads to the formation of some precipitation on the surfaces (Figures 1 and 2(b-d)). 3. Carrying out the loading and dyeing operations at the same time leads to an increase of the thin layer formed on the surface. In addition to this, such treatment paves the way for filling the pits formed after partial hydrolysis with alkali (Figures 1 and 2(e-g)). 4. It is worth mentioning that, carrying out loading with metal oxide NPs during dyeing with exhaustion or after dyeing wet operation with pad-drycure method leads to get fabrics with more homogeneous and smooth fabric surfaces. The abovementioned changes which took place on the surface topography of PET→H→B→D and PET/ CO→H→B→D fabrics loaded with TiO 2 , ZnO and SnO 2 NPs are a direct indication that these NPs are attached to the fabric surfaces.

Fourier transformation infrared (FT-IR)
Data in Tables 4 and 5 show the effect of dyeing wet operation on FT-IR absorption bands of functional groups in bleached, partially hydrolysed and dyed polyester fabrics loaded with different metal oxides NPs. Based on these data one can conclude the following: 1. The loading of dyed fabrics PET→H→B→D and PET/CO→H→B→D with NPs is affected on the absorption bands positions and the intensities of the carbonyl and hydroxyl groups, irrespective of the loading position with the above mentioned NPs during or after the dyeing wet operation (Tables 4  and 5). Tables 4 and 5  Stemming from the abovementioned one can conclude that, the C=O and OH¯ groups are affected as a result of loading PET→H→B→D and PET/CO→H→B→D fabrics with metal oxides (TiO 2 , ZnO and SnO 2 NPs). This happens irrespective of the nature of loaded NPs and the sequences of the loading process: during or after carrying out dyeing operation. In addition to this, the COO¯ groups, created on the fabrics surface after alkali treatment reacted with NPs forming a new chemical bond with such NPs. Similar findings have been reported. 19,20 The functional performances of polyester fabrics

Antimicrobial activity
Antimicrobial activity of bleached, partially hydrolysed and dyed (PET→H→B→D and PET/CO→H→B→D) fabrics loaded with TiO 2 , ZnO and SnO 2 NPs was evaluated by determining the reduction percentage of Gram-positive (Bacillus mycoides) -Gram-negative (Escherichia Coli), and nonfilamentous fungs (Candida albicans) bacteria using the shake flask method. Data given in Tables 6 and 7 illustrate the effect of finishing, the sequences used for loading the fabrics with NPs and the repeating washing on the percentages of colony forming units (% CFU) reduction on the above mentioned fabrics. Based on the data given in Tables 6 and 7, one can conclude the following: 1. In general, the loading of TiO 2 , ZnO and SnO 2 NPs on (PET→H→B→D and PET/CO→H→B→D) fabrics, led to the reduction of microbes on the surface of fabrics. This reduction depends on the         nature of NPs, the sequences of loading and the resistance towards repeated washings. 2. It was found that the sequence of loading with the above mentioned NPs during dyeing wet processing operations for polyester fabrics plays a very important role. This conclusion is based on the following: (a) The loading of TiO 2 and ZnO NPs on PET fabrics before carrying out the dyeing operation also leads to imparting antimicrobial properties to a lesser extent compared with those obtained after loading during or after dyeing operation (Tables 6 and 7). (b) The loading of TiO 2 and ZnO NPs using paddry-cure method after dyeing operation, led to obtaining polyester fabrics with 100% CFU reduction after one standard washing cycle with respect to the above mentioned three types of bacteria. It is worth mentioning that, the repeated washings of such fabrics did not cause a noticeable decrease in its ability for reduction of microbes. The data listed in Tables 6 and 7 illustrate that after five washing cycles, the fabrics still acquire excellent CFU reduction towards B.m and E.C. On the contrary, the application of SnO 2 NPs did not cause any noticeable improvement in the antimicrobial activity of such fabrics in comparison with those obtained after loading with such NPs directly after alkali treatment.
Based on the above mentioned, we can conclude that, the best method for loading partially hydrolysed, bleached and dyed polyester fabrics with TiO 2 and ZnO NPs for imparting high antimicrobial activity even after repeated washings should follow the sequence: 1-Bleaching; 2-Partial hydrolysis of fabrics using NaOH aqueous solutions; 3-dyeing polyester fabrics; 4-Loading partially hydrolysed, bleached and dyed polyester fabrics with TiO 2 and ZnO during dyeing using exhaustion operation or after carrying dyeing process using pad-dry-cure method.

Ultraviolet protection
The effect of the sequences of finishing with TiO 2 , ZnO and SnO 2 NPs on UV protection properties of bleached, partially hydrolysed and dyed polyester fabrics loaded was investigated. The obtained data listed in Tables 7 and 8  indicate the following: 1. In general TiO 2 and ZnO NPs are able to impart bleached, partially hydrolysed and dyed polyester fabrics UV protection properties compared to unloaded ones. On the contrary, the loading with SnO 2 NPs did not cause any noticeable improvement in such properties. 2. It was found that, the dyeing of (PET→H→B→D and PET/CO→H→B→D) fabrics was not accompanied with changing UPF rating after five washing cycles in comparison to the undyed fabrics. 3. The data in Tables 8 and 9 indicate that, the sequence of loading the applied NPs after, during or before carrying out the dyeing wet operation highly affect the UPF values of such fabrics as follows: (a) Loading the fabrics with TiO 2 NPs before, during or after dyeing wet operation leads to imparting PET fabrics good UV protection properties even after five standard washing cycles. The best result (UPF = very good) was obtained after loading TiO 2 simultaneously during the dyeing wet operation. (b) Loading PET→H→B→D and PET/ CO→H→B→D fabrics with ZnO and SnO 2 NPs after, or during dyeing operation causes a substantial increase in UPF (UPF = Excellent) even after five washing cycles. (c) Based on the listed data in Tables 8 and 9, one can conclude that loading ZnO and SnO 2 NPs during or after carrying the dyeing seems to be the ideal method for obtaining polyester fabrics with excellent UPF, even after five standard washing cycles.

Conclusion
The current study presents the effect of dyeing wet processing operation on the functional properties imparted to polyester fabrics loaded with different metal oxides nanoparticles. Characterization of PET and PET/CO dyed fabrics and loaded with TiO 2 , ZnO and SnO 2 NPs was carried out through SEM, EDX and FT-IR. The obtained results reveal that, NPs are chemically bonded to polyester fabrics, and that, the dyeing wet operation has no effect on this interaction. The antimicrobial activity of loaded and dyed polyester fabrics was tested. It has been found that, loading fabrics with TiO 2 and ZnO during or after carrying dyeing process paves the way for imparting outstanding antimicrobial activity even after five washing cycles, indicating their excellent laundering durability. It was also found that, the sequence of loading NPs after or during dyeing wet operation have a noticeable enhancement on the UPF values. According to the results discussed and presented above, one can conclude the feasibility of carrying out such modification on the wet processing line of polyester fabrics.