Glass Transition Temperature Of PET Research Articles

Directed evolution of an efficient and thermostable PET depolymerase

The recent discovery of IsPETase, a hydrolytic enzyme that can deconstruct poly(ethylene terephthalate) (PET), has sparked great interest in biocatalytic approaches to recycle plastics. Realization of commercial use will require the development of robust engineered enzymes that meet the demands of industrial processes. Although rationally engineered PETases have been described, enzymes that have been experimentally optimized via directed evolution have not previously been reported. Here, we describe an automated, high-throughput directed evolution platform for engineering polymer degrading enzymes. Applying catalytic activity at elevated temperatures as a primary selection pressure, a thermostable IsPETase variant (HotPETase, Tm = 82.5 °C) was engineered that can operate at the glass transition temperature of PET. HotPETase can depolymerize semicrystalline PET more rapidly than previously reported PETases and can selectively deconstruct the PET component of a laminated multimaterial. Structural analysis of HotPETase reveals interesting features that have emerged to improve thermotolerance and catalytic performance. Our study establishes laboratory evolution as a platform for engineering useful plastic degrading enzymes.

Structure-function analysis of two closely related cutinases from Thermobifida cellulosilytica.

Cutinases can play a significant role in a biotechnology‐based circular economy. However, relatively little is known about the structure–function relationship of these enzymes, knowledge that is vital to advance optimized, engineered enzyme candidates. Here, two almost identical cutinases from Thermobifida cellulosilytica DSM44535 (Thc_Cut1 and Thc_Cut2) with only 18 amino acids difference were used for a rigorous biochemical characterization of their ability to hydrolyze poly(ethylene terephthalate) (PET), PET‐model substrates, and cutin‐model substrates. Kinetic parameters were compared with detailed in silico docking studies of enzyme‐ligand interactions. The two enzymes interacted with, and hydrolyzed PET differently, with Thc_Cut1 generating smaller PET‐degradation products. Thc_Cut1 also showed higher catalytic efficiency on long‐chain aliphatic substrates, an effect likely caused by small changes in the binding architecture. Thc_Cut2, in contrast, showed improved binding and catalytic efficiency when approaching the glass transition temperature of PET, an effect likely caused by longer amino acid residues in one area at the enzyme's surface. Finally, the position of the single residue Q93 close to the active site, rotated out in Thc_Cut2, influenced the ligand position of a trimeric PET‐model substrate. In conclusion, we illustrate that even minor sequence differences in cutinases can affect their substrate binding, substrate specificity, and catalytic efficiency drastically.

Recycled polyethylene terephthalate/carbon nanotube composites with improved processability and performance

Recycled poly(ethylene terephthalate) (PET) nanocomposites containing multiwalled carbon nanotubes (CNTs) were prepared through melt compounding via masterbatch dilution method. The masterbatch and the nanocomposites were processed in a twin-screw extruder. The rheological, morphological, thermal and mechanical properties of the PET–CNT nanocomposites have been investigated. Incorporation of CNTs into recycled PET at low concentration (0.25 wt%) significantly increases the viscosity. The storage modulus and loss modulus of nanocomposites were also increased with increasing amount of CNTs. This effect was more pronounced at lower frequencies. The incorporated CNTs in recycled PET increase the degree of crystallinity and crystallization temperature through heterogenous nucleation. Thermal stability and glass transition temperature of PET–CNT nanocomposites were slightly higher than the reference recycled PET. The tensile strength and modulus of PET–CNT nanocomposites increased even at low concentrations of CNTs. Morphological investigation through scanning electron microscopy indicated homogeneous dispersion of CNTs at lower concentrations. At higher concentrations, the CNTs tend to agglomerate due to nanotube–nanotube interactions.

Thickness Effects on the Thermal Expansion Coefficient of Indium Tin Oxide/Polyethylene Terephthalate Film

Indium tin oxide/polyethylene terephthalate (ITO/PET) thin film/flexible substrates are widely applied in dye-sensitized solar cells, touch screens, and energy efficient windows, In this study, an application of the digital image correlation (DIC) method was used to determine the coefficient of thermal expansion (CTE) of ITO/PET thin films, and the effects of thickness variations of ITO and PET on the CTE of the samples. The observation range of the experimental temperature was selected from room temperature to the glass transition temperature of PET, which is 70°C. A novel DIC experimental process reduces errors caused by variations in the refractive index of the surrounding heated air is proposed. As a result, the error of the CTE measurement was reduced from 15 to 23% to less than 4%. The experimental results demonstrated that the CTE of the ITO/PET sample was anisotropic. Furthermore, the CTE of an ITO/PET sample increased by decreasing the thickness of PET flexible substrates, and increased by increasing the thickness of ITO film, and thus decrease the surface resistance of ITO film.

On the determination of the chemical reduction factor for PET geogrids

Data from four samples of commercially available PET geogrids (made either of yarns or bars), which were measured by BAM or other institute, are analyzed to discuss the procedure and problems of determining the chemical reduction factor RFCH associated with a certain service life. Estimates from Arrhenius extrapolation usually have very large statistical errors. The level of confidence must therefore be specified. A reliable estimate requires data from immersion tests below the glass transition temperature of PET. To extrapolate the time of reductions for each reduction factor at such low temperatures, one has to know the functional form of the mechanical degradation curve. It is shown how the degradation curve of the tensile strength may be obtained by determining the relation between increase in concentration of carboxyl end group (CEG) and decrease in tensile strength. Therefore, experimental studies to determine the chemical reduction factor should be accompanied by the measurements of the CEG concentration and the intrinsic viscosity. Furthermore, such measurements allow a non-ambiguous determination of the molecular mass. Hydrolytic molecular degradation will proceed continuously even at 20 °C with half-life of the inverse of the CEG concentration of 40–100 y. Nevertheless, small chemical reduction factors at a lifetime of 100 y are obtained with high level of confidence for materials with low initial CEG concentration and high molecular mass. This is shown by pooling data from samples with comparable CEG concentration, molecular mass and above all comparable intrinsic relation between increase in CEG concentration and decrease in strength. Therefore, the recommendation of ISO TR 20432, Table 2, for chemical reduction factors seems to be applicable to PET geogrids with index properties well below the one specified by the technical report. Whether these index properties are actually a sufficient condition to have small chemical reduction factors even at a very long service life is still an open question. The determination of chemical reduction factor should be based on aging experiments, at least for products with index properties close to the limiting values for the following reasons. (1) Even so standards are available, results of different laboratories on absolute values of CEG concentration and number averaged molecular mass differ to a certain extent. (2) Other factors, like crystallization, affect the mechanical degradation significantly. (3) There is no universally applicable form of the mechanical degradation curve.

D-Glucose-derived PET copolyesters with enhanced Tg

2,4:3,5-Di-O-methylene-D-glucitol (Glux-diol) and dimethyl 2,4:3,5-di-O-methylene-D-glucarate (Glux-diester) have been copolymerized with ethylene glycol and dimethyl terephthalate by polycondensation in the bulk to produce PET copolyesters as well as their respective homopolyesters. These sugar-based bicyclic monomers were synthesized from 1,5-D-gluconolactone, a commercially accessible compound derived from D-glucose. The PET copolyesters with either the diol or the diacid counterpart partially replaced by Glux had molecular weights in the 20000–40000 range and a random microstructure, and they were stable well above 300 °C. The PET copolyesters containing more than 10–15% of sugar-based units were amorphous while those displaying crystallinity were observed to crystallize from the melt at much lower rates than PET. The glass transition temperature of PET dramatically increased with the incorporation of Glux, whichever unit, diol or diacid, was replaced, but the enhancing effect was stronger in the former case. A preliminary evaluation of the mechanical behaviour of these copolyesters indicated that the genuine properties of PET were not substantially impoverished by the insertion of Glux. Compared to PET, the copolyesters exhibited a higher hydrolysis rate and an appreciable susceptibility towards biodegradation. The homopolyesters made of these sugar-based monomers could not be obtained with high enough molecular weights so as to be comparatively evaluated with copolyesters.

Crystallization and Mechanical Properties of Recycled Poly(ethylene terephthalate) Toughened by Styrene–Ethylene/Butylenes–Styrene Elastomer

Recycled poly(ethylene terephthalate) (R-PET) was blended with 15–30 wt% of styrene–ethylene/butylenes–styrene (SEBS) block copolymer and maleic anhydride grafted SEBS (SEBS-g-MA). Effects of nucleation and toughening of the elastomers were evaluated systematically by study of morphology, crystallization, thermal and mechanical properties of the blend. The addition of 30 wt% SEBS promoted the formation of co-continuous structure of the blend and caused the fracture mechanism to change from strain softening to strain hardening. Addition of SEBS-g-MA resulted in significant modification of phase morphology and obviously improved the impact strength. The compatibilization reaction of PET with SEBS-g-MA accelerated the crystallization of PET and increased the crystallinity. The shifts in glass transition temperature of PET towards that of SEBS-g-MA and the higher modulus for R-PET/SEBS-g-MA (70/30) blend found by DMA are also indications of better interactions under the conditions of compatibilization and interpenetrating structure.

Relationship of Surface Hydrophilicity, Charge, and Roughness of PET Foils Stimulated by Incipient Alkaline Hydrolysis

An enhancement of wettability of PET foils pretreated hydrolytically by immersing in mild alkaline (NaOH) solutions has been documented by a descending sigmoidal dependence between the interfacial free energy γSL of the PET/water interface and the concentration of NaOH solution cNaOH. An increase in temperature of the NaOH solution below the glass-transition temperature of PET further promotes the hydrophilicity, resulting in a proportional shift of the γSL vs cNaOH dependence. The limiting hydrophilicity of PET is thermodynamically predicted to occur at γSL → 0, corresponding to the advancing water contact angle θa ≈ 50° (for 6% NaOH and 60 °C). The surface roughness due to the partial hydrolytic degradation as well as the weight loss (dissolution) of PET are found to reach a maximum value just when the latter dependence goes through its inflection. Assuming a general parallelism between the interfacial free energy and the dissolution kinetics, we propose the hydrolytically stimulated formation and growt...

Miscibility of flame retardant epoxy resin with poly(ethylene terephthalate) and the characterizations of the blends

Epoxy resin containing bromine compound was melt blended with PET to obtain flame retardant polymer. The blend product was characterized by DSC, SEM, intrinsic viscosity and melt index measurements. The reaction between the epoxy group of DGEBBA (diglycidyl ether of brominated bisphenol A) and the carboxyl (or hydroxyl) end group of PET led to cross-linking of PET chains, and the intrinsic viscosity and melt index (MI) were increased in the range of equivalent amount of epoxy resin (within 1 %). DSC data revealed that the epoxy resin was not located in the crystalline region but was appeared in the amorphous region of PET matrix. Good miscibility of epoxy resin resulted in the decrease of crystallization temperature and glass transition temperature of PET. The blend was spun into fiber without any problems such as swelling or draw resonance, however, the mechanical properties were decreased as the amount of the DGEBBA was increased.

Visualization of structural rearrangements during annealing of solvent-crazed poly(ethylene terephthalate)

A direct microscopic procedure is used for studying structural rearrangements during the annealing of PET samples after solvent crazing. Even at room temperature, solvent-crazed PET samples experience shrinkage which is provided by processes taking place in crazes. This shrinkage is observed at temperatures up to the glass transition temperature of PET and proceeds via drawing together of crack walls. Once the glass transition temperature is attained during annealing, the spontaneous self-elongation of the polymer sample occurs. The mechanism of this phenomenon is proposed. The low-temperature shrinkage of the polymer sample is related to the entropy contraction of highly dispersed material in crazes that has a lower glass transition temperature than that of the bulk polymer. This shrinkage cannot be complete, owing to crystallization of the oriented polymer in the volume of the crazes. As a result of crystallization, the oriented and crystallized polymer in the crazes coexists with the regions of the unoriented initial PET. As the annealing temperature approaches the glass transition temperature of the bulk PET, its strain-induced crystallization takes place. As a result, the regions of the unoriented polymer between crazes are elongated along the direction of tensile drawing and the sample experiences contraction in the normal direction.

Metallization of poly(ethylene terephthalate) in the wide range of substrate temperatures

In this work, we present structural and compositional analysis of silver layers on PET and relation between the stress level and process conditions. The silver thin films (1 μm thickness) were deposited on PET (25 μm thickness) by electron beam evaporation in vacuum at different substrate temperatures (20, 40, 80 and 120 °C). The size of the crystal grain was obtained from the peak width of X-ray diffraction using the two major models known and employed in bulk materials: the integral breadth and the Warren–Averbach methods. The classical sin 2 ψ method of X-ray diffraction was used to measure the residual stresses in fine grained polycrystalline materials. The influence of metal coverage on interface composition, structure, morphology, and particle size of Ag/PET films has been studied employing X-ray photoemission spectroscopy (XPS), atomic force microscopy (AFM) and X-ray diffraction (XRD). According to the AFM and XRD, the structural changes in the polymer occurring above the glass transition temperature of PET ( T g ≈ 80 °C) may contribute to the morphological and stress changes in the Ag/PET system.

Poly(ethylene terephthalate) reinforced by N,N′-diphenyl biphenyl-3,3′,4,4′-tetracarboxydiimide moieties

Starting with 3,3′,4,4′-biphenyltetracarboxylic dianhydride and methyl aminobenzoate, we synthesized a novel rodlike imide-containing monomer, N,N′-bis[p-(methoxy carbonyl) phenyl]-biphenyl-3,3′,4,4′-tetracarboxydiimide (BMBI). The polycondensation of BMBI with dimethyl terephthalate and ethylene glycol yielded a series of copoly(ester imide)s based on the BMBI-modified poly(ethylene terephthalate) (PET) backbone. Compared with PET, these BMBI-modified polyesters had higher glass-transition temperatures and higher stiffness and strength. In particular, the poly(ethylene terephthalate imide) PETI-5, which contained 5 mol % of the imide moieties, had a glass-transition temperature of 89.9 °C (11 °C higher than the glass-transition temperature of PET), a tensile modulus of 869.4 MPa (20.2 % higher than that of PET), and a tensile strength of 80.8 MPa (38.8 % higher than that of PET). Therefore, a significant reinforcing effect was observed in these imide-modified polyesters, and a new approach to higher property polyesters was suggested. © 2002 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 40: 852–863, 2002; DOI 10.1002/pola.10169

Physicochemical Nature and Structural Dependence of the Unique Properties of Polyester Fibres

The structure and properties of PET and PET fibres are examined on three structural levels — molecular, supermolecular, and micromolecular. It was shown that the unique properties of the fibres are determined by the aliphatic-aromatic structure of PET and the chemically regular molecular structure. The structural dependence of the fundamental physicomechanical and physicochemical properties of PET and PET fibres was analyzed. It was shown that the high glass transition temperature of PET and PET fibres is determined more by molecular rigidity than by intermolecular interactions and varies little under the effect of moisture. This causes high stability of the structure in mechanical effects and exposure to heat and moisture, high reversibility of deformation, and insignificant creep under mechanical stresses. The structure and fundamental properties of PET and PET fibres are compared with the characteristics of other kinds of large-tonnage fibre-forming polymers and fibres and other aliphatic-aromatic polyesters and fibres. The advantages of using polyester fibres for fabrication of household and industrial articles are substantiated and summarized based on an examination of the properties of these fibres.

A study on the surface free energy of modified silica fillers and poly(ethylene terephthalate) fibers by inverse gas chromatography

The surface free energy of modified silica fillers and poly(ethylene terephthalate) (PET) fibers was analyzed by inverse gas chromatography in order to investigate the relationship between their surface characteristics and the performance of the composite formed from these materials. The adsorption isotherms of n-heptane and 1-propanol were determined by the elution-peak-maximum method. The dispersive and polar components of the surface free energy were determined by use of the Young–Dupre equation and the Fowkes equation on the basis of the saturated spreading pressure derived from the Gibbs adsorption equation. The acidity and the basicity of the surface were estimated by the specific retention volume of each probe molecule with different donor number and acceptor number. It was found that the dispersive component of the surface free energy for modified silica fillers was mostly lower than that for original silica filler. The polar component of the surface free energy for ethylene glycol modified silica filler became large, while that for n-butanol modified silica filler decreased remarkably. It was also found that original silica filler exhibited high acidity, while modified silica fillers exhibited low acidity. Although these methods have been applied to PET fibers, the surface free energy could not be determined quantitatively because of the surface change during the pretreatment of PET fibers. It was observed that the polar component of the surface free energy decreased when the pretreatment was made at a temperature higher than the glass-transition temperature of PET. It became clear that the interaction between modified silica fillers and PET fibers correlated well with the basicity of the fillers, but not with their acidity.

High-pressure DSC study of thermal transitions of a poly(ethylene terephthalate)/carbon dioxide system

The thermal transitions of a poly(ethylene terephthalate)/carbon dioxide (PET/CO 2) system were investigated by using a differential scanning calorimeter accessorized with a high-pressure DSC cell. It was found that the glass transition temperature of PET decreases with an increase in the CO 2 pressure due to the plasticization effect, which is quite noticeable even at rather low CO 2 pressures. The sorbed CO 2 enhances the mobility of the chain segments and depresses the crystallization temperature of the PET. The CO 2-induced crystallization of PET at high pressure is attributed mainly to the plasticization effect, which causes a lower T g than room temperature for PET, and hence crystallization of PET can occur at room temperature. The sorbed CO 2 was also found to be able to induce the crystallization of PET at temperatures lower than the glass transition temperature of PET. The results of high-pressure DSC were supported by measurements of wide-angle X-ray diffraction (WAXD).

Studies of post drawing relaxation phenomena in poly(ethylene terephthalate) by infrared spectroscopy

AbstractIn this paper, we study the relaxation behavior of initially amorphous poly(ethylene terephthalate) (PET) films drawn, at 80°C using a draw rate of 2 cm/min, to a draw ratio (λ) from 1 to 5 and then quenched to room temperature. These films were then heated at different temperatures from 68 to 80°C for different times and their orientation determined. The orientation measurements were performed by transmission infrared spectroscopy and the bands used for the determination of orientation were those at 1340 and 970 cm−1 for the trans conformers, normalized using the 1410 cm−1 benzene ring vibration. The crystallinity was determined by thermal analysis. It is shown that when PET is drawn to λ values up to 2–2.5 (before stress‐induced crystallization), the orientation relaxes rapidly at temperatures close to the glass transition temperature of PET. For λ values of 3 or higher, the orientational relaxation of the amorphous regions is hindered. This effect is ascribed to the development of strain‐induced crystallites, which are believed to act as pseudo‐crosslinks.

Solvent-induced crystallization of amorphous poly(ethylene terephthalate)fiber in chlorine substituted hydrocarbons.

Some chlorine substituted aliphatic hydrocarbons exhibit strong interaction with amorphous undrawn poly (ethylene terephthalate) (PET) fiber. For example, solvent-induced crystallization in trichloroethylene develops within few seconds at 333-353K and even initiates at 256K. This fact suggests that the glass transition temperature of PET is depressed about 110K with the solvent. The spherulites develop from the surface to the center of fiber with the penetration of solvent and the transverse of fiber can be divided into two parts which are spherulite part and amorphous part. Apparent diffusion coefficient of trichloroethylene is estimated to be in the range from 3.35×10-7 to 7.05×10-5cm2/s and that of 1, 1, 1-trichloroethane to be in the range from 1.44×10-8 to 1.52×10-6cm2/s. Apparent activation energies are about 18 and 39kcal/mol, respectively. The stress-strain behavior is directly affected by the progress of solvent-induced crystallization.

Effect of heating and aging on microstructure of polyester‐polyamide copolymer

AbstractPolyester‐polyamide (PET/PA) copolymers offer a wide range of possible applications where both dimensional stability and good impact resistance can be achieved from their synergism. In order to ensure these properties for long‐term use, however, problems of phase separation, volume change, and chemical reequilibration on heating or aging must be identified and overcome. Wide‐angle x‐ray diffraction (WAXD), small‐angle x‐ray scattering (SAXS), and thermal analysis were employed to follow the microstructure of a 70:30 PET/PA copolymer with several different processing histories as a function of heat history and both short‐term and long‐term aging. Heating the copolymer, as received, above the melting temperature of PET caused phase mixing. The effect of heating on crystallinity depended on starting crystallinity. Holding the copolymer at 50°C, just below the glass transition temperature of PET, caused phase separation in samples which had been annealed for 30 min at 150°C. On long‐term aging samples gave evidence of phase mixing. The results indicate highly nonequilibrium structure in the material, regardless of the original processing.

CRYSTALLIZATION OF POLY (ETHYLENE TEREPHTHALATE) IN ORGANIC SOLVENT

The amorphous and undrawn poly (ethylene terephthalate) (PET) was treated with several kinds of organic solvents and silicon oil at temperatures of -10°C to 200°C, and the fine structure was investigated by means of X-ray diffraction (wide-angle and small-angle) and density gradient tube. The degree of swelling of PET treated with benzyl alcohol, benzene, tetrachloroethylene, and chloroform increased with the rise of treatment temperature. On the other hand, the degree of swelling of PET treated with dimethyl formamide (DMF), dimethyl acetoamide, and nitrobenzene at -10°C_??_75°C increased with a lowering of temperature. This unusual swelling behavior of PET was discussed on the basis of the interaction between PET and organic solvent. The degree of crystallinity of PET treated with organic solvent increased with the rise of temperature in every case. The crystallization was almost completed up to about 10°C in DMF and benzene. Acceleration of the crystallization in organic solvent may be attributed to the fact that the glass transition temperature of PET is lowered in organic solvent. The dominant selective uniplanar orientation of (100) plane was found for the PET which was treated with DMF in lower temperature.

Studies of the Solvent Dyeing of Poly(ethylene terephthalate) with Disperse Dyes from Trichloroethylene and Isooctane

Abstract The diffusion of 1,4-dihydroxyanthraquinone and C. I. Disperse Orange 3 in poly(ethylene terephthalate) (PET) from the trichloroethylene (TRI) and isooctance (ISO) dyebath was investigated by the method of the cylindrical film-roll. The stability of PET in TRI and ISO at high temperatures was also examined. The degradation of PET by solvents was in the following order: water>TRI>tetrachloroethylene (TCE) and ISO. The diffusion coefficients of Orange 3 from various solvents at 90°C were in the order: TRI>TCE>water>ISO. The activation energy of diffusion from ISO was much larger than that from TRI, the latter being nearly identical to that from TCE. The Arrhenius plots of the diffusion coefficients in PET indicated some transitions. The glass transition temperature of PET in TRI was lower than that in TCE. The diffusion coefficient and the surface concentration of Orange 3 from ISO were increased by the addition of water, while those from TRI were not changed within the range of experimental error.