Correlation between the shade of an azo disperse dye on poly(ethylene terephthalate) and poly(lactic acid) fibres with its spectroscopic properties in selected organic solvents

A series of azo disperse dyes was synthesised and the purified, synthesised dyes were characterised by proton nuclear magnetic resonance, thin‐layer chromatography and melting point measurement. The spectroscopic properties of the dyes in solution were studied by dissolving the dyes in ethyl acetate and methyl benzoate. These were seen as mimicking the environment of the dye when inside dyed poly(lactic acid) and poly(ethylene terephthalate), respectively. Reflectance spectra of the dyes on both polyester substrates were also measured in order to correlate with the spectroscopic properties of the dyes in solution. The absorbance spectra of the dyes in solution exhibited a hypsochromic (lower wavelength of maximum exhaustion) shift when dissolved in ethyl acetate, compared with methyl benzoate. The occurrence of this yellow shift was attributed to the lower polarity of ethyl acetate compared with methyl benzoate. The colour of the dyes in ethyl acetate solution was also brighter and stronger (higher molar extinction coefficients) than that in methyl benzoate. Most of the synthesised dyes exhibited high levels of exhaustion onto the two polyester fabrics. However, the visual colour yields, for those dyes having approximately the same high level of exhaustion, were different, the dyed poly(lactic acid) being stronger (higher K/S value) as well as being yellower and a trace brighter than the dyed poly(ethylene terephthalate). This difference correlated well with the solvatochromic study of the dyes in ethyl acetate and methyl benzoate solution.     

Dyeing of poly(lactic acid) fibres with synthesised novel heterocyclic disazo disperse dyes

Poly(lactic acid) (PLA) is the first melt‐processable, renewable, sustainable and biodegradable natural‐based synthetic fibre. It has a broad range of uses and combines ecological advantages with outstanding performance in textiles. PLA fibre, as an aliphatic polyester, can be dyed with disperse dyes. Apart from the limited number of commercial disperse dyes, disperse dye exhaustion on PLA is generally lower than that on  poly(ethylene terephthalate) (PET). In this study, new heterocyclic disazo disperse dyes, substituted with methyl, nitro and chloro groups at their ortho‐, meta‐ and para‐ positions, synthesised in our previous study, were applied to PLA and PET fibres to examine their dyeing performance, and colour fastness and dye exhaustion properties. Different shades of yellow, orange, reddish brown and brown were obtained. Most of the synthesised novel heterocyclic disazo disperse dyes exhibited good build‐up properties with high K/S levels on both fibres. Para‐ bonding substituent provided higher K/S values than meta‐ and ortho‐ positions for –NO₂ and –Cl substituents for both fibres. Overall, the most synthesised novel heterocyclic disazo disperse dyes in this study exhibited good build‐up properties with high K/S, exhaustion and wet fastness levels on both PLA and PET fibres.      

Thermal analysis of heat set poly(ethylene terephthalate) fibres

Differential thermal analysis (d.t.a.) has been used for characterization of the thermal history of poly(ethylene terephthalate) (PET) fibres. The latter were treated under a variety of temperatures and times in a manner similar to conditions employed in conventional textile processing. The d.t.a. revealed an endotherm at temperatures below the main melting peak of the fibre polymer, related directly to temperature and time of thermal treatment, even with yarns that were heat set for less than 0.2 sec (e.g. false twisting process). The maximum of this low temperature endotherm is a direct measure of the effective temperature (T_eff) that has been acquired by the PET fibres during the thermal processing. In practice, several thermal treatments are often involved in textile processing. Results of this work imply that PET fibres subjected to a second heat treatment will show an additional low temperature endotherm on d.t.a. scanning, provided that the structural characteristics formed in the first thermal process are not neutralized in the second thermal process and recrystallizable material is still present in the fibre polymer.     

Substituent effects on the photofading of disperse azo dyes on poly(ethylene terephthalate) substrate

The relationships between the chemical structures and oxidative fading of the disperse azo dyes, p‐nitrophenylazo‐ and benzothiazoleazo‐anilines, on poly(ethylene terephthalate) substrate are discussed in terms of the parameters k_0,i (rate constants of reaction towards ¹O₂) and f_i (photosensitivity), the molecular parameters of molecular orbital theory and substituents in the diazo and coupling components, on the assumption that the initial rates of oxidative fading are proportional to the product of k_0,i and f_i. 2‐Methoxy‐5‐acetylamino‐N‐substituted aniline couplers exhibited large f_i values. 2‐Chloro and 4‐nitro substituents of aniline diazo components exhibited small f_i values or high quantum yields of internal conversion, while 4‐nitro substituent did not. A close correlation between N‐substituents and light fastness, proposed by Müller and supplemented by Dawson, demonstrates the applicability of frontier orbital theory, through the highest occupied molecular orbital (HOMO) energy of the dyes, to the analysis of oxidative fading. Dyes with N‐2‐cyanoethyl substituents, which gave a lower HOMO energy, also exhibited superior light fastness compared with N‐2‐hydroxyethyl substituents.     

Thermal oxidative degradation kinetics and thermal properties of poly(ethylene terephthalate) modified with poly(lactic acid)

The thermal oxidative degradation kinetics of poly(ethylene terephthalate) (PET) copolymers modified with poly(lactic acid) (PLA) were investigated with thermogravimetric analyzer (TGA). The thermal properties of the modified products were also determined by differential scanning calorimeter (DSC) technique. Waste PET (P100) obtained from postconsumer water bottles was modified with a low‐molecular‐weight PLA. The PET/PLA weight ratio was 90/10 (P90) and 50/50 (P50) in the modified samples. The thermal oxidative degradation kinetics of the modified samples was compared with those of PET (P100). The segmented block and/or random copolymer structure of the modified samples formed by a transesterification reaction between the PLA and PET units in solution and the length of the aliphatic and aromatic blocks were found to have a great effect on the degradation behavior. On the basis of the results of the degradation kinetics determined by Kissinger method, the degradation rate of the samples decreased in the order of P50 > P90 > P100, depending on the amount of PLA in the copolymer structure. However, the degradation activation energies (E_A) of the samples decreased in the order of P100 > P90 > P50. It was concluded that the degradation rate and mechanism were affected significantly by the incorporation of PLA into the copolymer structure. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

The dyeing of poly(lactic acid) fibres with disperse dyes using ultrasound: Part 2 - Fastness

The use of ultrasound imparted greater colour strength to 1% omf dyeings of five of six disperse dyes studied, both before and after reduction clearing and had no effect on either the colour or λ_max of the dyeings. The lower fastness obtained to both wet and dry rubbing as well as to the first two/three of the five repeated wash cycles was attributed to the greater colour strength of the dyeings imparted by the use of ultrasound during dyeing.     

The dyeing of poly(lactic acid) fibres with disperse dyes using ultrasound: Part 1 - Initial studies

Six disperse dyes were applied at 0.5%, 1% and 2% omf depths of shade to poly(lactic acid) fabric at 30-80 °C for 20, 50 and 90 min in both the presence and absence of ultrasound. Whilst ultrasound enhanced the colour strength obtained for three of the six disperse dyes used at temperatures upto 70 °C, ultrasound did not always result in enhanced colour strength being achieved in the case of the three other dyes. The observed intensification of colour strength was attributed to dye disaggregation. Dyeing at 80 °C in the presence of ultrasound resulted in pale, dull dyeings of reduced colour strength, which was attributed to breakdown of the dye dispersions at this particular temperature.     

Dyeing and fastness properties of phthalimide‐based alkali‐clearable azo disperse dyes on poly(ethylene terephthalate)

The properties of a series of phthalimide‐containing azo disperse dyes and azo dyes with N‐methyl phthalimide moieties in their diazo component were investigated and compared when used to colour polyethylene terephthalate. The N‐substitution of the phthalimide gave a hypsochromic effect on the colour change and better colour yields on poly(ethylene terephthalate) fabrics, probably because of the electron‐donating property of the methyl group and the higher hydrophobicity of phthalimide‐containing azo dyes compared with those containing phthalimide moieties. The results show that phthalimide‐based azo disperse dyes have excellent dyeing fastness properties and that high wash fastness can be achieved using alkali clearance. This alternative clearance method is important for reducing the environmental impact of the dyeing process by replacing reductive clearing and, in particular, by removing the need for sodium hydrosulphite, which creates a high biological oxygen demand when released in conventional disperse dyeing effluent and which generates aromatic amines.     

Correlation of solubility data of azo disperse dyes with the dye uptake of poly(ethylene terephthalate) fibres in supercritical carbon dioxide

Solubility data of disperse azo dyes in supercritical carbon dioxide are presented for dyeings of poly(ethylene terephthalate) fibres with CI Disperse Red 167:1, carried out at 200–300 bar and 80–120 °C, with varying amounts of adulterants. The same dyeings were also carried out in water for comparison. Scanning electron micrographs were taken of the dyes which show a growth of dye crystals during treatment in supercritical carbon dioxide. The paper reports that at 120 °C, melting of the pure dye CI Disperse Red 167:1 is observed. The presence of adulterants in the dye formulations help prevent agglomeration by acting as spacers between the dye molecules. Dyeings of PETP carried out under conditions of the highest solubility of the dye in supercritical carbon dioxide do not necessarily result in a very high dye uptake. This was shown by pressure- and temperature-dependent dyeing experiments of PETP in supercritical carbon dioxide.     

Radiation grafting to poly(ethylene terephthalate) fibres

Polyethylene terephthalate (PET) monofilaments were grafted with styrene in methylene chloride solution using both the mutual and preirradiation methods. Good yields were obtained, the grafted fibres were dissolved and the graft copolymer and both homopolymers separated by various techniques. The graft copolymers were hydrolysed with potassium hydroxide in benzyl alcohol to destroy the PET backbone. The molecular weights were determined by osmometry. The G values of grafted side chains were 0.57 and 0.10 per 100 eV for the mutual and preirradiation methods, respectively. The corresponding fractions of PET grafted were 0.24 and 0.11. Less than 4% homopolymer was produced by either method. The yields contrast with radical yields measured by e.s.r. of only 0.025. It is suggested that the high grafting yields are due to the methylene chloride facilitating the accessibility of the monomer to the active sites created by the radiation rather than by the increased yields of radicals by chain transfer. Chlorine, for example, did not lead to increased yields even in the presence of methylene chloride. Presumably, in the mutual grafting system, radicals are available for grafting, which are too labile to be detected by e.s.r. In the case of the preirradiation method, the yields are also higher than the radical yields. This may be due to a regenerative chain transfer mechanism.     

Nonisothermal crystallization kinetics and morphology of poly(ethylene terephthalate) modified with poly(lactic acid)

The nonisothermal crystallization kinetics of poly(ethylene terephthalate) (PET) copolymers modified with poly(lactic acid) (PLA) were investigated with differential scanning calorimetry, and a crystal morphology of the samples was observed with scanning electron microscopy. Waste PET (P100) obtained from postconsumer water bottles was modified with a low‐molecular‐weight PLA. The PET/PLA weight ratio was 90/10 (P90) or 50/50 (P50) in the modified samples. The nonisothermal melt‐crystallization kinetics of the modified samples were compared with those of P100. The segmented block copolymer structure (PET‐b‐PLA‐b‐PET) of the modified samples formed by a transesterification reaction between the PLA and PET units in solution and the length of the aliphatic and aromatic blocks were found to have a great effect on the nucleation mechanism and overall crystallization rate. On the basis of the results of the crystallization kinetics determined by several models (Ozawa, Avrami, Jeziorny, and Liu–Mo) and morphological observations, the crystallization rate of the samples decreased in the order of P50 > P90 > P100, depending on the amount of PLA in the copolymer structure. However, the apparent crystallization activation energies of the samples decreased in the order of P90 > P100 > P50. It was concluded that the nucleation rate and mechanism were affected significantly by the incorporation of PLA into the copolymer structure and that these also had an effect on the overall crystallization energy barrier. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2007     

Radiation graft-copolymerization kinetics of poly(ethylene terephthalate) fibres

A theoretical analysis of radiation grafting kinetics has been made in terms of the quantitative interrelationship between the degree of grafting (G_f), the grafting periods (t) grafting temperature (T) and the monomer content in the polymeric system (M). Poly(ethylene terephthalate) fibres and a number of hydrophilic monomers have been employed for these experiments. The grafting reactions were initiated by trapped radicals produced by irradiation of the polymeric system under vacuum at room temperature. Experimental results showed that the monomer content in the fibres obeyed the Arrhenius relationship. The overall activation energy of the grafting reaction has been calculated. Grafting reactions can proceed only if ΔE_t > ΔE_p + ΔE_M. This termination activation energy ΔE_t is a function of the state of polymeric system.     

Some sorption characteristics of poly(trimethylene terephthalate) with disperse dyes

Sorption characteristics, such as sorption kinetics and isotherms, relation between dye sorption and shade development of poly(trimethylene terephthalate) (PTT) and their comparison with poly(ethylene terephthalate) (PET), were reported. Results from two different dyeing rate studies, dyeing rate under constant temperature and under changing temperature, were examined to obtain the common rate constants, and to obtain information for the design of dyeing temperature profile and holding time. Rate constants of PTT were compared with that of PET. Sorption isotherms of disperse dyes on PTT were also studied. Both Nernst and Langmuir models were examined. The dye uptake ability of PTT was compared with PET. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 86: 223–229, 2002     

Radical yields in irradiated poly(ethylene terephthalate) fibres

The formation of free radicals and their subsequent decay in irradiated polyethylene terephthalate monofilaments was studied by e.s.r. under a variety of conditions. A yield of 0.023 radicals per 100 eV was found, in agreement with the literature values. Reduced values were found in the presence of water, methylene chloride and chlorine. The decay followed a two-stage second order pattern presumably due to radicals in the crystalline and amorphous regions. At ?196°C, G values of 0.7 of trapped electrons were found, rapidly decaying as the temperature was raised. At about ?135°C the signal changed to the characteristic signal found at room temperature with a G value of 0.42. On adding methylene chloride to irradiated PET, comparatively rapid decay of the trapped radicals took place, the rate corresponding closely to the rate of sorption of the methylene chloride into the monofilaments. This indicated very rapid decay even from the crystalline regions, once the solvent is present. A number of other observations are presented and interpreted in relation to, for example, the radiation grafting yields in the presence of solvents.     

Thermal crosslinking of collagen immobilized on poly(acrylic acid) grafted poly(ethylene terephthalate) films

Graft polymerization of acrylic acid onto plasma‐treated poly(ethylene terephthalate) (PET) films was used to prepare surfaces suitable for collagen immobilization by dip‐coating. Such surfaces could be used as matrices for smooth muscle cell cultures in tissue engineering. Contact angle measurements showed that plasma‐treated and grafted PET films undergo considerable surface reorganization during storage under ambient conditions. However, after collagen immobilization the contact angle remained relatively stable. The amount of collagen initially attached to the film surface increased with increasing poly(acrylic acid) graft density, but subsequent washing in water led to significant collagen loss. This loss could nevertheless be substantially reduced by thermal crosslinking of the collagen in the range 110–130 °C. Atomic force microscopy (AFM) observations suggested that the washed crosslinked collagen has a very similar structure to that of the un‐crosslinked collagen. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 85: 1874–1880, 2002     

Preparation and biodegradation of copolyesters based on poly(ethylene terephthalate) and poly(ethylene glycol)/oligo(lactic acid) by transesterification

The poly(ethylene terephthalate‐co‐ethyleneoxide‐co‐DL ‐lactide) copolymers were successfully prepared by the melt reaction between poly(ethylene terephthalate), poly(ethylene glycol), and DL ‐oligo(lactic acid) without any catalysts. The transesterification between ethylene terephthalate, ethyleneoxide, and lactide segments during the reaction was confirmed by the ¹H NMR analysis. The effect of reaction temperatures and the starting feed ratios on the molecular microstructures, molecular weights, solubility, thermal properties, and degradability of the copolyesters was extensively studied. The values of crystallization temperature, melting temperature, crystallization, and melting enthalpy of the copolyesters were found to be influenced by the reaction temperatures, starting feed ratios, etc. The copolyesters showed good tensile properties and were found to degrade in the soil burial experiments during the period of 3 months. The morphology of the copolyester films were also investigated by scanning electron microscopy during soil burial degradation. POLYM. ENG. SCI., 2010. © 2009 Society of Plastics Engineers     

Microwave‐assisted dyeing of poly(butylene terephthalate) fabrics with disperse dyes

In this study, conventional heating and microwave dielectric heating in the exhaust dyeing of poly(butylene terephtalate) fabrics with disperse dyes were studied in order to determine whether microwave heating could be used to increase the dyeability of poly(butylene terephtalate) fibre in shorter processing times and enable dyeings of adequate wet fastness to be obtained. Accordingly, the samples of 100% poly(butylene terephtalate) single jersey knitted fabric were dyed with CI Disperse Yellow 160 and CI Disperse Yellow 42, CI Disperse Red 177 and CI Disperse Red 91, CI Disperse Blue 79:1 and CI Disperse Blue 54 at 98 °C with or without microwave dielectric heating. The colouristic properties, colour fastnesses and the tensile properties of the dyed fabrics were investigated and compared with each other. Microwave dielectric heating is regarded as a tool for ‘green chemistry’ and provides many advantages over conventional heating without any deterioration in the properties of the dyed materials. Microwave heat dyeing enhances the exhaustion and the fixation of dye, and good colour fastnesses and repeatability in dyeings are achieved in short heating times of the dyebath.     

Anisotropy of dielectric relaxation in poly(ethylene terephthalate) fibres

Dielectric measurements have been made on poly(ethylene terephthalate) (PET) fibres in the frequency range 0.5–10 kHz in temperature range ?120°?+30° C with the applied electric field parallel and perpendicular to the fibre axis. Considerable directional anisotropy was observed in the β-relaxation process, which was independent of frequency. The observed dielectric anisotropy has been related to the structural parameters thus leading to a value 〈cos²ψ〉 = 0.21, where ψ is the angle between the dipole moment vector responsible for this relaxation and the molecular chain axis. Activation energy for this process in PET fibres (9 kcal/mol) was lower than that reported for PET films and extruded rods.     

Fundamental studies on solvent dyeing with tetrachloroethylene. I. Diffusion of disperse dyes in poly(ethylene terephthalate)

The diffusion of C.I. disperse Violet 1 and Violet 8 in poly(ethylene terephthalate) (PET) was investigated by the method of cylindrical film roll. The effect of tetrachloroethylene (TCE) on the properties of PET was also studied. The treatment of PET with TCE brought about a strong effect on the thermal properties without degradation of PET. The diffusion of disperse dyes in PET from the TCE dyebath was faster than that from the aqueous dyebath. The activation energies of diffusion in the temperature range of 60° to 95°C from the TCE dyebath were smaller than those from the aqueous dyebath. Some break points were observed in the Arrhenius plots of diffusion coefficients in PET from the TCE dyebath. They were lower than those observed at dry and water-swollen states.     

Analysis of photofading of phenylazo-indole and phenylazo-N-ethanolaniline disperse dyes on poly(ethylene terephthalate) fabric using the PM5 method

The photofading behaviors of phenylazo-N-(ethanol)aniline and phenylazo-indole, nitrohetarylazo-N-substituted aniline disperse dyes on poly(ethylene terephthalate) (PET) substrate were analyzed using the Kubelka-Munk (K/S) parameters of the dyed fabrics exposed to a carbon arc in air. The initial experimental slopes (K_PET) of fading on PET were estimated from the time profiles of the K/S values at the λ_max. The rates (k_0,i) of reaction of these dyes with ¹O₂ were estimated by frontier orbital theory using the PM5 method. The photosensitivities (f_i) of the dyes were estimated from the K_PET assuming that the K_PET values are proportional to the product of k_0,i and f_i. Dyes with small f_i values, irrespective of their k_0,i values, possess excellent lightfastness (LF), while dyes with larger f_i values possess poorer LF. The validity of estimating k_0,i values by the MO method was confirmed experimentally by analyzing the mutually photosensitized fading behaviors of combination dyeings.