Biothermoplastics from Renewable Resources

Keywords

PTT • Renewable resource • Biopolymer • Propanediol • Drawing • Annealing • Fiber properties • Orientation • Crystallinity • PTT dyeing • Solid state polymer­ization • Hybrid yarn

PTT is one of the more recently manufactured synthetic fiber that is derived from renewable resource. Companies such as Shell chemical company and Dupont are manufacturing PTT on a commercial scale and are selling the fibers under the trade names of Corterra and Sorona, respectively [03Duh]. PTT is said to have excellent resiliency and softness and also chemical stability and stain resistance which makes them particularly suitable for carpet applications. PTT is produced in a two-step process, similar to the common polyester (polyethylene terephthalate). In the first step, terephthalic acid (TPA) is esterified using 1,3-propanediol or transesterified using dimethyl terephthalate. The second step involves polycondensation of the esterified or transesterified product to remove the polycondensation byproducts until the desired molecular weight is reached. It is the use of 1,3-propanediol that is derived from an renewable resource that makes PTT fibers eco-friendly. Two distinguishing features of producing PTT compared to PET are the use of a titanium catalyst instead of the antimony catalyst and a considerably lower polycondensation temperature. Due to the use of low polycondensation temperatures, the cost of producing PTT is considerably higher than that of PET. In addition, PTT has a melting temperature 20-30 °C lower than that of PET and a low initial modulus that provides high flexibility to the fibers [01Lyo]. The high extensibility of PTT fibers is attributed to the arrangement and orientation of the polymers in the chain. The chemical structure of PTT is shown in Fig. 64.1, PTT fibers have — O-(CH2)3-O bond conformation with a concentration of the repeating units and opposite incli­nation of successive phenylene groups along the chain which force the molecular chain to assume a extended zigzag configuration. The helical structure of PTT with an angle of 60 ° provides an opportunity to extend the PTT chain by drawing during

Take-up speed (m/min)	Density (g/cm3)	Tenacity (g/den)	% Crystallinity	Boil-off shrinkage (%)
2,000	1.316	1.6	25	38
3,000	1.319	2.2	30	20
4,000	1.322	2.8	38	10
5,000	1.326	3.0	39	3
6,000	1.343	3.2	40	3
7,000	1.346	3.3	40	3

fiber production (zone-drawing) and improve the tensile properties of the fibers [01Lyo].

Although the chemical composition of PTT is similar to that of PET, the structure of PTT is considerably different. PTT has odd number of methylene units between the terephthalates compared to PET which has three methylene units [01Kim]. In PTT, the propylene glycol segment assumes the trans — gauchegauche-trans conformation in the crystalline phase with two monomers forming a 2/1 helix compared to the all-trans conformation seen in PET. The phenyl groups in the PTT chain are inclined in opposite directions with an angle of 52° between the terephthaloyl residues [04Fri]. Such a structural arrangement provides unique properties to PTT, for instance, outstanding resiliency and chemi­cal resistance. The morphology of PTT fibers was found to evolve in three distinct stages. First, an oriented noncrystalline region is formed leading to an increase in density. This is followed by an increase in the order in the oriented noncrystalline phase which causes crystallization. Finally, an increase in the oriented and non-oriented region occurs with decrease in the amorphous regions.

The influence of take-up speeds (winding speeds) during fiber spinning on the structure and properties of PTT fibers was investigated. Initial modulus of the PTT fibers did not change with increasing speeds whereas the fiber crystallinity, density, and heat of fusion increased [ 11 Kim]. T able 64.1 provides the changes in some of the properties of the PTT fibers with increasing speed. Increase in density and % crystallinity with increasing take-up speed was reported to be due to stress-induced crystallization. At high take-up speeds, small rigid crystallites are formed along the fiber axis leading to decreased birefringence. Substantial decrease in boil-off shrink­age with increasing take-up speed is due to the increased crystallinity and orientation. In a similar study, Wu et al. have studied the effect of take-up velocities between 0.5 and 8 km/min on the structure and properties of the fibers [02Wu]. Fibers processed below 4 km/min were found to have a predominantly amorphous structure whereas those processed above 4 km/min were crystalline. As seen in Fig. 64.2 increasing take-up speeds increased the orientation and crystallinity as evident from the

Fig. 64.2 X-ray diffraction image of PTT fibers produced at three different spinning speeds. Substantial increase in the orientation and crystallinity of the fibers is observed with increasing spinning speeds [02Wu]. Reproduced with permission from Elsevier

diffraction arcs becoming sharper and brighter. In addition, cold crystallization decreased substantially at higher take-up speeds whereas the melting temperature remained relatively stable. Similarly, tensile strength was found to increase with increasing take-up speed whereas elongation remained decreased and modulus was constant [02Wu]. Fibers obtained had strength up to 3.4 g/den and initial modulus was 20 g/den [02Wu]. Studies on in situ crystallization of PTT have shown that crystallization occurs in stages and lamellar tips grow in the edge-on and flat-on configurations [08Iva]. As seen in Fig. 64.3 crystal growth was not uniform and large regions of amorphous materials were observed. Based on measurement of birefrin­gence, it was found that a sudden increase in crystalline fraction occurred when the take-up speed was between 4 and 5 km/min [08Kim].

PTT with two different viscosities and molecular weight was blended and melt extruded to form crimp fibers [06Oh]. One of the PTT components had a molecular weight of 30,100 and viscosity of 1.02 compared to molecular weight of 26,967 and viscosity of 0.92. By changing the draw ratio, fibers having fineness between 1.3

Fig. 64.3 Time-lapse images (8.5 min interval) of the crystallization of PTT show that crystals grow edge-on (area 1 in a) and side-on (area 2 in b). Large amorphous regions are also seen (areas marked 3 in b-d) [08Iva]

and 1.4 denier with various crimp levels were obtained. As seen in Fig. 64.4, fibers had a circular cross-section and crimped to various extents before and after treating in boiling water [06Oh]. Various cross-sectional shapes of the fibers varying from round, peanut, dog bone, and pear-shaped were obtained by changing the crimping conditions [09Luo]. Various shapes of PTT/PET fiber cross-section were detected, such as round, peanut, dog bone, and pear-like shapes, as shown in Fig. 64.5, which were obtained by varying the crimping conditions [09Luo].

Dyeing behavior of PTT fibers was compared with PET fibers at constant and changing temperatures. Several dyeing kinetic parameters and isotherms were reported as given in Table 64.2. It was found that the dyeing rate was controlled by the rate of diffusion of the dye and that smaller dye molecules had higher dyeing rate [02Yan]. The % dye exhaustion for PTT was similar to that of PET fibers even though the dyeing temperature was 100 °C for PTT compared to 130 °C for PET. It was suggested that 100 °C was most suitable for dyeing PTT and that the tempera­ture should be well controlled above 70 °C to obtain uniform dyeing [02Yan].

To improve the dyeability of PTT, a dye fixing additive was introduced into the polymer before extrusion [06Hsi, 07Shu, 09Wan] that enables dyeing of PTT using

Fig. 64.4 Images showing the cross section (a), crimped nature of the bicomponent fibers before (b), and after boiling in water (c) [06Oh]. Reproduced with permission from John Wiley and Sons

(с) X55 (d) ST 100 Fig. 64.5 Various cross sections of PTT fibers obtained by changing the crimping conditions [09Luo]. Reproduced with permission from Sage publications

acid dyes. Ability to dye the fibers with acid dyes will reduce the cost of dyeing, provide wide range of colors and bright shades, and possibility of dyeing PTT along with wool and nylon. In one such attempt to improve dyeability of PTT, copolyamides were synthesized and blended and later co-extruded into fibers in the presence of an compatibilizer (Surlyn) [09Wan]. Mechanical properties of the

Table 64.2 Some of the dyeing parameters for PTT fibers dyed with various disperse dyes [02Yan] C. I. Disperse dye Half-dyeing time (min) Dyeing rate constant k (x 103 min) Diffusion rate constant (x 103 min) % Dye exhaustion Type Mw PTT PET Red 60 332 4.9 2.08 5.4 99 97 Red 82 439 4.3 2.54 8.5 91 81 Red 167:1 506 1.0 11.42 27.4 — — Blue 56 305 4.6 2.47 8.2 89 94 Blue 79 639 7.3 1.53 4.5 88 80

Table 64.3 Changes in the mechanical properties of the PTT fibers at various concentrations of the additives [09Wan] DETA content Additive content (WF) Tensile strength Extension at break (MF) Copolyamide Surlyn (g/den) (%) 0 0 0 0.58 29.63 0.20 0.06 0 0.51 24.79 0.225 0.04 0 0.53 25.81 0.225 0.06 0 0.50 22.74 0.25 0.06 0.02 0.47 20.25 0.25 0.08 0 0.44 21.78 0.25 0.08 0.02 0.42 17.16 0.25 0.10 0 0.28 9.23 0.25 0.10 0.02 0.26 9.34 0.25 0.12 0 0.25 9.43 0.25 0.12 0.02 0.21 8.87

fibers did not show any major change when the additive in the blend was less than 0.1 % but decreased substantially at higher concentrations of the additives as seen in Table 64.3. Tensile strength of the fibers obtained was considerably low compared to the strength of normal PTT and the remarkable decrease in tensile properties at higher concentration of the additives was suggested to be due to the morphological and/or thermodynamic immiscibility. As seen in Table 64.4, substantial improve­ment in dye uptake was observed with the inclusion of the additive due to the presence of polar groups and also due to the reduction in % crystallinity and increase in accessibility of the fibers to dyes and chemicals.

In a similar approach, PTT and cationic dyeable PTT (CD-PTT) were blended and extruded at a temperature of 265 °C in a capillary rheometer [06Hsi]. After extrusion, a portion of the fibers were drawn three times to produce fully drawn yarns. Table 64.5 provides information of some of the properties of the PTT and CD-PTT used to produce the blend fibers. DSC studies indicated that the PTT and CD-PTT components were miscible and the melting temperature decreased with

DETA content (MF)	Additive content (WF)	Dye uptake (%)
Copolyamide	Surlyn
0.20	0.06	0	55.18
0.225	0.04	0	60.65
0.225	0.06	0	65.13
0.25	0.06	0.02	91.59
0.25	0.08	0	95.83
0.25	0.08	0.02	88.34

Table 64.4 Dye uptake of the PTT fibers with various levels of additives [09Wan]

Property	PTT	CD-PTT
Intrinsic viscosity (dL/g)	0.88	0.76
5-Sodium sulfonate dimethyl isophthalate	—	2
Mw (g/mol)	34,000	23,000
Mw/Mn	1.92	1.91
R-COOH (meq/kg)	18	20
Tm (° C)	229.1	225.3
Td (°C)	358	351

Table 64.5 Characteristics of PTT and CD-PTT chips used to prepare the blend fibers

increase in the content of 5-SSDMI. However, the crystallinities decreased with increase in the proportion of CD-PTT in the blend. Similarly, the tenacities of the PTT/CD-PTT blend fibers also decreased as the 5-SSDMI increased as shown in Fig. 64.6. Similar results were also obtained by [07Shu].

Table 64.6 Comparison of the average SSP rates of PTT and PET at 220 °C [03Duh] Fiber Intrinsic viscosity (dL/g) Mn % COOH ends Pellet size (g/100) SSP time to reach Mn of 21,600 (h) Average SSP rate (pmol/g/h) PTT 0.445 8,700 9.6 1.6 6.86 19.9 PET 0.36 8,800 35.5 1.6 15.50 8.7 PTT 0.54 11,100 5.6 2.5 4.84 18.0 PET 0.42 11,000 28.2 2.5 10.72 8.3 PTT 0.66 14,300 10.7 2.3 1.90 24.9 PET 0.5 14,200 31.4 2.3 4.4 10.9

Increasing drawing speed was found to increase the total degree of molecular orientation in both the crystalline and amorphous regions. Contrarily, increasing drawing speed decreased the crystallization temperature but increased crystal size. A continual increase in strength and modulus of the fibers was observed with increase in take-up velocity and draw ratio at all drawing temperatures studied [01Lyo].

To overcome the limitation of PTT production through melt-polymerization, a combination of melt and solid state polymerization (SSP) was proposed [03Duh]. It was reported that PTT does not pose the stickiness problem during SSP and the rate of polymerization of SSP was more than twice that of PET as seen in Table 64.6. Continuous SSP of PTT could be done at 225 °C and it was therefore suggested that a combination of melt and SSP could provide economical fiber grade PTT. The crystallization kinetics of PTT were studied by Chuah and they reported that PTT had a crystallization rate between that of PET and poly(butylene terepthalate) (PBT). Although PTT had odd number of methylene units in it structure, it did not follow the previous understanding that odd numbered polyesters were difficult to crystallize [01Chu]. Polarized optical microscope images show the presence of spherulitic PTT as seen in Fig. 64.7.

Hybrid PTT fibers were prepared by mixing two types of organoclay (IMD-MMT and C12PPh-MMT) with 1,3-propanediol (PDO) and heating the mixture up to 265 °C. Crude solid obtained was washed with water, dried, and later extruded into fibers at 250 °C in a capillary rheometer [06Cha]. Fibers were drawn to various extents and the effect of drawing on the mechanical properties and thermal stability was studied. Table 64.7 provides a comparison of the thermal behavior of the pure and hybrid PTT fibers. The organoclay showed intercalated and partially exfoliated features and had well-dispersed individual clay layers. As seen in Table 64.8, inclusion of the organoclay increased the strength and modulus for the IMD-MMT clay but decreased for the C12PPh-MMT clay due to debonding between the organoclay and the matrix polymer and due to the presence of many nano-sized voids caused by excessive stretching of the fibers. Drawing of the fibers at slow speed resulted in glass transition followed by cold crystallization, and the extent of cold crystallization was in turn dependent on initial crystallinity [01Gre].

Fig. 64.7 Optical images showing the spherulitic morphologies of PTT/aPET after crystallization at 190 °C. Ratio of PTT/aPET was 100/0 (a); 90/10 (b); 80/20 (c); 70/30 (d); 60/40 (e); and 50/50 (f) [10Chi]. Reproduced with permission from John Wiley and Sons

Blends of polypropylene (PP), PTT, and nanoclay were prepared and the properties of the fibers were studied [12Hez]. In addition to virgin PP, maleic anhydride grated PP was also blended to improve biocompatibility. SEM images (Fig. 64.7) showed that the PTT and PP were immiscible and PTT appeared as a disperse phase with irregular shapes. Addition of nanoclay decreased the interpar­ticle distance and the size of the dispersed PTT phase. Thermal analysis and X-ray diffraction also showed that the two polymers were not compatible. Table 64.9 provides a comparison of the thermal and crystalline parameters of the PP, PTT, and their blends. Addition of nanoclay and compatibilizer provided improved mechanical properties.

PTT was blended with poly(ether esteramide) (PEEA) with the addition of various amounts of ionomers such as lithium-neutralized poly(ethylene-co- methacrylic acid) copolymer (EMAA-li) and sodium neutralized poly(ethylene- co-methacrylic acid) copolymer (EMAA-Na) [11Kob]. Different effects were

Table 64.7 Comparison of the thermal properties of pure and hybrid PTT fibers containing different extents of clay and at varying draw ratios [06Cha] IMD-MMT C12PPh-MMT % Draw Intrinsic Tm Td Intrinsic 7m Td Clay ratio viscosity (°С) (°С) Residue, 600 °С (%) viscosity (°С) (°С) Residue, 600 °С (%) 0 1 0.84 228 362 1 0.84 228 362 1 1 1 0.81 232 367 8 — — — — 2 1 0.80 232 370 10 0.86 227 371 10 3 1 0.85 232 372 11 0.83 228 370 11 3 — 233 371 11 — — — — 7 — 232 372 10 — — — — 9 — 232 371 10 — — 4 1 — — — — 0.81 227 371 12 3 — — — — — 228 370 12 7 — — — — — 227 370 13 9 — — — — 228 371 13

Table 64.8 Tensile properties of pure and hybrid PTT fiber containing various levels of organoclay and at different draw ratios [06Cha] % Clay Draw ratio IMD-MMT C12PPh-MMT Strain (g/den) Modulus (g/den) Elongation (%) Strain (g/den) Modulus (g/den) Elongation (%) 0 1 0.26 14.2 2 0.26 14.2 2 3 0.28 14.8 2 0.28 14.8 2 7 0.28 15.5 2 0.28 15.5 2 9 0.28 16.2 3 0.27 8.2 3 1 1 0.35 19.4 2 — — — 3 0.38 20.6 2 — — — 7 0.37 20.8 2 — — — 9 0.36 21.2 2 — — 2 1 0.36 19.7 2 0.34 20.9 2 3 0.36 20.3 2 0.32 20.6 2 7 0.38 20.7 3 0.33 20.3 2 9 0.37 21.6 2 0.33 20.6 2 3 1 0.36 20.3 2 0.36 22.1 3 3 0.37 21.2 3 0.36 21.9 2 7 0.38 22.7 2 0.30 22.0 2 9 0.38 22.6 3 0.30 21.9 2 4 1 — — — 0.38 24.7 2 3 — — — 0.37 24.8 3 7 — — — 0.32 24.7 3 9 — — — 0.33 24.3 2

Table 64.9 Thermal properties and crystallinity of the PP, PTT, and MAPP blend fibers with and without the nanoclay [12Hez] Samples (PP/PTT/ MAPP/Nanoclay) 7m of PP (°C) 7m of PPT (°C) Crystallinity, PP (%) Crystallinity, PTT (%) Total crystallinity (%) 100/0/0/0 166.5 — 37.03 — 37.03 0/100/0/0 — 231.3 — 23 23 70/25/5/0 167.7 229.2 42.2 33.92 40.1 60/35/- 167 229.3 39.62 19.7 38.2 75/25/5/0 167.9 229.4 50 25.58 41.5 79/15/5/1 166.7 228.5 47 23 40.6 75/15/5/5 167.3 228.8 47.15 19.9 38.25

observed with the different ionomers. Table 64.10 provides a comparison of the changes in thermal properties of the PTT/PEEA blends with various levels of ionomers.

Several researchers have attempted to produce PTT blend fibers with an attempt to improve quality and performance of the fibers. Padee et al., have blended PTT

Table 64.10 Thermal properties of various blends of PTT/PEEA with and without ionomers [1 IKob] Heating Cooling Te TCc А Ясс Tm Tc ДЯ ATc Tc. for PEEA Degree of crystallinity Sample (°С) (°С) (J/g) (°С) (°С) (J/g) (°С) (°С) {%) PTT 45.9 72.4 36.5 229.1 172.6 45.4 17.2 — 31.2 PTT/25 % PEEA 44.2 69.6 29.1 228.1 153.7 32.7 32.0 108.9 29.9 PTT/10 % E/MAA-Li 44.6 68.3 35.6 227.5 171.5 47.9 18.7 — 36.5 PTT/10 % E MAa-Na 44.4 69.2 1.5 227.3 198.1 50.9 5.0 — 38.8 PTT/25 % PEEA/10 % E/MAA-li 44..4 70.3 20.3 227.0 173.5 35.2 18.1 126.3 37.2 PTT/25 %/PEEA/20%E-MAA — li 43.5 69.0 19.6 226.9 175.7 26.3 17.7 137.9 32.8 PTT/25 % PEEA/10 % E MAA-Na 45.5 — 0 227.6 200.3 37.5 5.7 123.3 39.6 PTT/25 % PEEA/20 % E/MAA-Na 44.6 — 0 227.6 199.0 30.3 5.2 125.3 37.8

Table 64.11 Thermal properties and crystallinity changes for the neat and blend fibers [13Pad] PLA PTT Fiber Tm (°C) Tc (°C) Xc (%) Tm (°C) Tc (°C) Xc (%) PLA 152.6 — 18.2 — — — 90:10 151.0 88.0 19.5 226.6 189.1 7.8 80:20 151.4 92.7 21.9 226.5 186.0 11.7 70:30 150.5 95.3 20.6 227.1 185.3 23.8 60:40 148.1 94.7 22.9 226.9 182.1 26.2 50:50 149.7 95.7 13.4 227.9 182.0 51.0 PLA — — — 230.7 183.7 80.9

with PET in various ratios but found that the two polymers were not compatible and it was difficult to produce fibers. Contrarily, Liang et al. have reported that PTT and PET were completely miscible and formed homogenous blends [08Lia]. Various blends of the PTT and PET fibers were found to have a single glass transition temperature and cold crystallization temperature. In addition, polymer-polymer interaction parameter, melt crystallization temperature, and homogeneity of the fracture surfaces observed using scanning electron microscopes were provided as evidence of the miscibility of PTT and PET [08Lia]. Although fibers could not be produced from higher ratios of PET and PTT, fibers were produced from a blend of 10 % PTT and 90 % PET by extruding at a temperature of 250 °C [13Pad]. Melting temperature of both PTT and PET decreased when either fraction was increased and was attributed to the decrease in crystal size. However, crystallization temperature increased with increasing ratio of one polymer in another. Some of the thermal and crystallinity parameters of the pure and blend fibers are shown in Table 64.11. DSC and polarized light microscope suggested significant nucleation and crystallization rate enhancement for PTT by the addition of EMAA-Na. However, addition of lithium ionomer did not enhance PTT nucleation and crystallization [11Kob]. Morphologically, the PEEA was found to segregate into domains of EMAA-Li and EMAA-Na and the ionomer domains were partially or completely covered by PEEA. Such a distribution of the polymers resulted in core-shell morphology that provided synergistic static decay.

The tensile modulus and strength showed a moderate increase with increasing levels of PTT but the 50/50 blend fibers had considerably lower strength than that of PTT fibers. In addition to the ratio of the two polymers in the blend, it has been shown that the type of weave and crimp configuration also affect the properties of the fabrics made from PTT/PET blends [10Luo]. Woven fabrics made from PTT/PET blends were highly elastic and the elasticity could be controlled by varying the fiber production conditions [10Luo].

Instead of blending two synthetic polymers, Wang and Sun developed blends of PTT and cellulose acetate butyrate (CAB) that would make the fibers more environmentally friendly [11Wan]. PTT was reactive melt mixed with maleic anhydride (MA) and blends were later prepared with various ratios of PTT/CAB

Table 64.12 Tensile properties of the various ratios of PTT and cellulose acetate butyrate blend fibers [11Wan] Fiber blends Tensile strength (g/den) Elongation at break (%) PTT/CAB (100/0) 0.40 ± 0.02 390 PTT/CAB (80/20) 0.32 ± 0.03 194 PTT/CAB/PTT-g-MA (70/20/10) 0.38 ± 0.02 234 PTT/CAB (70/30) 0.34 ± 0.02 80 PTT/CAB (50/50) 0.36 ± 0.02 60 PTT/CAB (30/70) 0.37 ± 0.02 20 PTT/CAB (20/80) 0.37 ± 0.02 6 PTT/CAB (0/100) 0.43 ± 0.02 72

and PTT/CAB/PTT-g-MA. Fibers were extruded from a Brabender twin screw extruder at a temperature of 240 °C and screw speed of 100 rpm. SEM studies of the fracture surface of the blend fibers showed that the CAB was evenly distributed in the PTT matrix but PTT and CAB were thermodynamically immiscible. Thermal studies showed that the blend fibers have better thermal stability than the individual neat polymers. To improve properties of the fibers, grafting of MA onto PTT was done and in addition, several compatibilizers were added to enhance the interfacial adhesion. Tensile properties in Table 64.12 show that blends had inferior properties than the neat polymers and addition of compatibilizers significantly increased the tensile strength. To develop PTT nanofibers, PTT was blended with cellulose acetate butyrate and in situ fibrillation was achieved during melt processing [12Li]. In this approach, two immiscible polymer blends were mixed together and melt extruded. Later, the matrix polymer (cellulose acetate) was removed. PTT fibers with average diameter of 145 nm were obtained using this approach. The extruded fibers formed bundles similar to yarns as seen in Fig. 64.8. It was suggested that the nanofibers could be assembled into fabrics for various uses [12Li].

An investigation on the dyeing behavior of PTT fibers showed that unlike PET, PTT could be dyed at 100 °C under atmospheric conditions using disperse dyes. However, higher temperatures (110-120 °C) produced deeper shades. Table 64.13 shows the K/S values of PTT and PET dyed at different temperatures using three different disperse dyes. As seen in the table, PTT fibers have considerably higher shade depth at any given temperature for all the three dyes studied [03Mad]. Dyed fibers showed good fastness to washing, crocking, and light. In a similar study, poly (trimethyelene-co-butylene-terephthalate) copolymer filaments were found to have better dyeability and could be dyed at room temperature [09Zou]. The kinetics of dyeing PTT with an azo disperse dye (C. I. Disperse Red 82) was studied by Ovejero et al. [07Ove]. Dyeing rate was found to increase with temperature and acceptable exhaustions were not obtained even above dyeing temperature above 80 °C. How­ever, a dye exhaustion rate of 90 % was obtained when the dyeing was done at 90 ° C [07Ove].

Fig. 64.8 Digital images of the PTT nanofibers formed after removing the CAB. SEM images show the formation of nanofiber bundles (a, b) [12Li]. Images c and d show the longitudinal and cross-sectional views, respectively. Reproduced with permission from John Wiley and Sons

Table 64.13 Comparison of the shade depth between PTT and PET fibers when dyed with three different disperse dyes at various temperatures Type of disperse dye Dyeing temperature (°C) K/S value PTT PET Blue 56 100 16.4 6.0 110 18.1 9.6 120 17.6 13.5 130 15.1 12.6 Blue 73 100 19.8 3.6 110 29.3 8.3 120 30.1 18.2 130 27.6 20.6 Blue 79 100 11.5 2.6 110 15.1 6.0 120 18.2 OO OO 130 16.4 11.3

Polyblend fibers of poly(trimethylene terephthalate) and cationic dyeable poly (trimethylene terephthalate) were produced in various ratios and the dyeing behav­ior was studied. Unlike PTT, CD-PTT contains 5-sodium sulfonate dimethyl

H-foKHjhOOC-O-COtaOH + 2NaOH — и-г<ХСН2)3оос-0-со-}-пои + NaOOC—(3^COONa + HO(CH2)3OH

Table 64.14 Some of the PTT depolymerization parameters [01Kim] Reaction rate constants in ethylene glycol Alkaline depolymerization rate constants Solubility Temp (°C) *1 (min-1) *2 (min-1) Reaction medium *1 (min-1) *2 (min-1) parameter [(cal/cc)1/2] 160 0.0085 0.0140 Ethylene glycol 0.0102 0.0140 16.08 170 0.0108 0.0262 Diethylene glycol 0.0195 0.0271 14.60 180 0.0294 0.0541 Triethylene glycol 0.0326 0.0407 13.44 190 0.0450 0.1203 Diethylene glycol monoethyl ether 0.0524 0.1927 10.90

isophthalate (5-SSDMI) that contains the sulfonate (SO3Na) groups and therefore can be easily dyed. The polymer blends could be considered to be miscible but the addition of 5-SSDMI decreased the tensile properties and crystallinity of the fibers [06Hsi].

Since PTT is a thermoplastic polymer, it would be feasible to reprocess and use thermoplastic products from PTT. To understand the potential of converting PTT waste into successful products, the effects of reaction media, composition, temper­ature, and rate of depolymerization of PTT were studied [01Kim]. Figure 64.9 shows the mechanism of alkaline hydrolysis of PTT. As seen from the figure, the products obtained after depolymerization of PTT are ethylene glycol and disodium terephthalate. It was found that the depolymerization occurs in two stages believed to be due to the twisted and crumpled configuration of the polymers. Some of the depolymerization parameters that were obtained during the study are given in Table 64.14.

In a similar study, the surface alkaline hydrolysis of PTT filaments at high spinning speeds was investigated with an aim to obtain more porous and hydro­philic fiber surface [04Kot]. Increasing spinning and hydrolysis time had a direct effect on the weight loss of the fibers which varied from 5 to 30 %. A more predominant effect on weight loss was observed when the spinning speed was increased at heat setting temperatures between 100 and 180 °C. Substantial weight loss of up to 70 % was observed when the heat setting temperature was 180 °C and the spinning speed was about 2,000 m/min. However, the weight loss decreased to about 50 % when the spinning speed was 6,000 m/min [04Kot]. Changes in the

2000 пУпжп 3000 nVmn 4000 пУпіп

5000 пУпіп 6000 пУпіп Fig. 64.10 SEM images depicting the surface morphology of the fibers at different spinning speeds when extruded at 86 °C for 90 min and heat setting at 180 °C. Substantial formation of pores is seen on the surface of the fibers [04Kot]. Reproduced with permission from John Wiley and Sons

morphology of the fibers after hydrolysis at 86 °C for 90 min at various spinning speeds and heat setting at 180 °C are shown in Fig. 64.10. As seen from the figure the fibers have considerable number of pores and under these conditions, the pore size varied from 1 to 1.2 pm [04Kot].

PTT is preferable for carpet applications due to its high resiliency. However, PTT is mostly made in the staple form whereas bulk continuous filaments (BCF) are preferred for carpets [04Chu]. PTT has also been made into BCF by extruding the polymer at a melt temperature of 250-265 °C into multiple filaments that are cooled by air, drawn between two hot air rollers, and texturized into BCF. It was found that PTT BCF bulk development during heat treatment is a function of the DUO II yarn preheating temperature and the texturing air temperature.

The high surface reflectance of polyesters including PTT and PET poses problems in obtaining dark shades on the fibers. Several approaches have been used to modify the surface of PET and decrease the surface reflectance. In one such approach, PTT-PET blend fabrics were UV irradiated to create micro and nanoscale roughness through photoxidation [06Jan]. SEM images in Fig. 64.11 clearly show the increase in roughness (58 nm to 122 nm at a UV dose of 9.5 J/cm2) of the fibers after the UV treatment. When dyed with Disperse Red 60 and C. I. Disperse Blue 56, both the UV irradiated PET and PTT fabrics showed no deterioration in dyeability and similar shade depth (K/S) values [06Jan]. However, lightness

Fig. 64.11 SEM images of the surface of fibers in the PTT and PET fabric before and after irradiation show the marked difference in the surface [06Jan]

decreased due to irradiation before and after treatment when dyed with black disperse dyes [06Jan]. The dyed fabrics also showed excellent colorfastness to laundering and rubbing.

References

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