Continuous-distribution kinetics for degradation of polybutylene terephthalate (PBT) in supercritical methanol

The depolymerization of polybutylene terephthalate (PBT) in supercritical methanol was investigated by using a batch autoclave reactor. Continuous kinetics analysis was applied to experimental data. It was observed that PBT could dissolve into supercritical methanol quickly and decompose completely in a homogeneous phase. PBT with average molecular weight of about 29 700 was converted to oligomer with that of 4200 within 10 min and with that of 2700 in 15 min at 513 K and converted into monomer completely within 22 min. The main reaction products decomposed of PBT were dimethylterephthalate (DMT) and 1, 4-butanediol (BG) by methanolysis. The yields of monomer components of the decomposition products, including byproducts were measured. The yields of DMT and BG could reach 94.5% and 70.1%, respectively, at 563 K for 75 min. Based on the qualitative and quantitative analyses of the products, a depolymerization-reaction scheme was proposed to explain the reaction mechanism, i.e. the degradation of PBT in supercritical methanol mainly includes random scission and chain-end scission reactions and side reactions for monomer components. With the process of degradation, some oligomers could be decomposed into small molecular products by side reactions. Continuous-distribution kinetics theory was developed to analyze the decomposition behavior. The energy of activation for the random scissions of PBT in the supercritical methanol was 86.53 kJ/mol.     

Process analysis of depolymerization polybutylene terephthalate in supercritical methanol

The characteristics of depolymerization of PBT in supercritical methanol were investigated in the range of 453-533 K by using a high-pressure reactor. Based on the qualitative and quantitative analyses of the products, a depolymerization-reaction model was proposed to explain the depolymerization and reaction mechanism, i.e. ester exchange reaction occurred randomly along the chain of PBT. It was suggested that the process of depolymerization consisted of subcritical region, transitional region and supercritical region. In the first region, PBT mainly showed a swelling process in the methanol with slow decrease in molecular weight and little conversion. In the second region, PBT dissolved quickly with high depolymerization rate. While in the third region, the molecular weight of PBT decreased quickly with a thorough depolymerization in few minutes. DMT and BG obtained from the depolymerization of PBT in supercritical methanol reached 98.5% and 72.3%, respectively.     

The use of melt rheology and solution viscometry for degradation study of post-consumer poly(ethylene terephthalate): The effects of the contaminants,reprocessing and solid state polymerization

Rheological measurements and intrinsic viscosity were performed to determine how the presence of contaminants, reprocessing and solid state polymerization (SSP) affects the degradation of post-consumer poly(ethylene terephthalate) (PET). First, post-industrial PET resin was contaminated with a series of surrogates according to a US-FDA protocol to simulate the worst-case scenario of misuse of PET packaging. The samples were submitted to recycling and SSP process in the presence of surrogates. The rheological data demonstrated that contaminated samples present degradation, even without any additional process. However, when the contaminated samples are submitted to melt extrusion the level of degradation increases. For the SSP process it was found that the surrogates do not interfere in the degradation process. In addition, an empirical analysis was derived based on the existing relationship. This analysis allowed the use of complex viscosity in higher frequencies, that is, out of the Newtonian plateau, and it shows to be as efficient as the zero-shear rate viscosity, allowing to associate the molar mass index of different samples. The data were corroborated from those obtained by the viscometric molar mass index, highlighting the importance of this new method to quantify the degradation in the polymer system.     

Dynamic behavior of surface charge on gamma-ray irradiated polybutylene naphthalate

Polymer insulating materials used in radioactive environment can be degraded by discharge which is induced by surface charge accumulation. Hence the stability of the electrical insulation is dependent upon the dynamic behavior of surface charge that may be changed by irradiation. In this paper, polybutylene naphthalate was employed as test sample to investigate the effects of gamma-ray irradiation on the charge behavior. The samples were previously irradiated in air up to 100 kGy and then up to 1000 kGy with dose rate of 10 kGy/h using a ⁶⁰Co gamma-source. The experiment was carried out under a negative dc stress between two aluminum plate electrodes. An electrostatic probe was designed to measure the charge density. Obtained results show that with the increase of the total dose of the irradiation, both the capacity of surface charge and the rate of charge decay decrease. It is proposed that the charging behavior depends upon the density of localized surface states that is reduced by the radiation induced cross-linking reactions. The decay is caused by the recombination of surface charge with ions of the opposite sign in air.     

The Degradation of Poly(ethylene terephthalate)

The penetration of new markets by polyester fibers has emphasized the need for increased stability of the polyester toward a variety of degradative reactions. Extensive studies of the nature of the thermal, hydrolytic, oxidative, and radiation-induced degradation reactions have been reported. The interpretation of kinetic investigations and the identification of the reaction products have been facilitated by using suitable esters as model compounds in place of the polymeric species.     

The selective recycling of mixed plastic waste of polylactic acid and polyethylene terephthalate by control of process conditions

The glycolysis of postconsumer polyethylene terephthalate (PET) waste was evaluated with catalysts of zinc acetate, zinc stearate and zinc sulfate, showing that zinc acetate was the most soluble and effective. The chemical recycling by solvolysis of polylactic acid (PLA) and PET waste in either methanol or ethanol was investigated. Zinc acetate as a catalyst was found to be necessary to yield an effective depolymerization of waste PLA giving lactate esters, while with the same reaction conditions PET remains as an unconverted solid. This provides a strategy to selectively recycle mixed plastic waste by converting one plastic to a liquid and recovering the unreacted solid plastic by filtration.     

Production of valuable hydrocarbons by catalytic degradation of a mixture of post-consumer plastic waste in a fluidized-bed reactor

A mixture of post-consumer plastic waste (PE/PP/PS/PVC) was pyrolyzed over various catalysts using a fluid catalytic cracking (FCC) process operating isothermally at ambient pressure. Experiments with various catalysts gave good yields of valuable hydrocarbons with differing selectivity in the final products dependent on reaction conditions. A model based on kinetic and mechanistic schemes for the observed products associated with chemical reactions and catalyst deactivation has been developed. The model gives a good representation of experimental results. It is also an improvement on the currently available empirical “lumping” techniques which are usually severely restricted in terms of product definitions. Additionally, this model represents the benefits of product selectivity for the chemical composition in relation to the effect of structurally different catalyst types, and the performance of the reaction temperature used as well as the particle size of the catalyst selected.     

Catalytic degradation of polyethylene using thermal gravimetric analysis and a cycled-spheres-reactor

Commercial samples of pure polyethylene were decomposed over H-ZSM-5 and Y-type zeolites using thermal gravimetric analysis (TGA) and a laboratory-scale-plant, so-called the cycled-spheres-reactor. By the TGA measurements, the activity and the deactivation behavior of the zeolite catalysts were determined. The plastic to catalyst ratio was varied to find out the optimal value for catalyst screening and for the operation of the cycled-spheres-reactor. In addition, the deactivation behavior of the zeolite catalysts was investigated. Y-type zeolites revealed lower activity and faster deactivation behavior than H-ZSM-5. Higher module of H-ZSM-5 and Y-type zeolite showed slower deactivation, but lower activity than lower module of those. Experiments in the cycled-spheres-reactor proved the results of the TGA measurements in terms of activity. The main products in the non-catalytic degradation were waxes, and when catalysts were applied, a high yield of oils was obtained at the expense of waxes. The product spectra of product oils obtained with catalysts lay mainly in the range C₄–C₁₀.     

Determination of polybutylene terephthalate polycondensation equilibrium constant using a batch reactor

The PBT polycondensation equilibrium constant at 255°C was determined using a batch reactor. Starting from a Polybutylene terephthalate (PBT) prepolymer having a degree of polymerisation of 12.7, equilibrium experiments were performed in the range of 1 to 50 mbar. The equilibrium degree of polymerisation (i) was determined indirectly using dilute solution viscometry of a solution of 1 weight % PBT in m - cresol. The degree of polymerisation of PBT obtained at equilibrium in the range of 1 to 50 mbar at 255°C as a function of the BDO partial pressure (mbar) could be expressed by: i = 111.47 − 86.18 exp(−1.14 equation/tex2gif-stack-1.gif). The equilibrium solubility of 1,4 butanediol (BDO) in the PBT melt was derived form the BDO partial pressure using the Flory - Huggins theory. The PBT polycondensation reaction equilibrium constant was related to the degree of polymerisation by the equation: in the range i = 26 − 100. The PBT polycondensation equilibrium constant at high degrees of polymerisation is in line with literature data and thermodynamics.     

PET,PBT结晶过程Avrami方程的探讨

用解偏振光法研究了PET,PBT以及PET-PBT,PBT-PBI共聚物在不同条件下的等温结晶过程.结果表明,Avrami指数n值和结晶速度常数随条件不同呈明显规律变化,且n值在绝大多数情况下不成整数.由此提出了这样的假设:n值是一个与晶核中结晶生长点数目相关的参数.     

Reaction to fire of recycled poly(ethylene terephthalate)/polycarbonate blends

In the present paper, we study the effect of both morphology and compatibilization on the reaction to fire of blends of recycled poly(ethylene terephthalate) (PETr) with recycled polycarbonate (PCr). It is shown that while the flame retardancy of blends containing less than 50% w/w of PCr increases almost linearly with PCr content, blends containing more than 50% w/w of PCr react to fire like pure PCr. This change of reaction to fire correlates with the formation of a continuous PCr phase in the blend.The compatibilization of the blend by a trans-esterification reaction leading to the formation of copolymers at the interface decreases the overall fire performances due to PETr chain breaking as a side effect which results in a strong decrease of blend viscosity and of the temperature at which mass loss begins.     

Effect of dissolution-based recycling on the degradation and the mechanical properties of acrylonitrile-butadiene-styrene copolymer

A dissolution-based recycling technique for acrylonitrile-butadiene-styrene copolymer (ABS) is proposed, and the effects of repeated recycling cycles are studied measuring changes in chemical structure, melt viscosity, and tensile and impact properties. Acetone as solvent, 0.25 g/ml concentration, room temperature and 40 min for dissolution have been found to be the most reliable recycling parameters. FTIR, DSC and MFI results have shown that the dissolution-based recycling itself does not degrade the ABS. However, TGA analysis suggests that during the dissolution some stabilizers are probably eliminated, and consequently degradation takes place in the following injection moulding step. Darkening of recycled ABS is attributed to the butadiene degradation, pointed out by FTIR results. Otherwise, the chemical structure of the SAN matrix has not been modified, but its molecular weight has been reduced. The modulus of elasticity is not affected even after four recycling cycles. However, yield stress and impact strength decrease after the first recycling cycle, and remain constant in the following steps.     

Effects of nanosilica on crystallization and thermal ageing behaviors of polyethylene terephthalate

The effects of nanosilica(Si O2) on crystallization and thermal aging behaviors of polyethylene terephthalate(PET) have been studied using differential scanning calorimetry(DSC) and polarized optical microscopy(POM), viscometry, tensile testing and scanning electron microscopy(SEM). For non-isothermal and isothermal crystallizations, the crystallization rate of PET increases considerably with increasing content of Si O2 providing a large number of nucleation sites, but the relative crystallinity of the nanocomposites has little differences with that of neat PET. According to POM observation, the nucleation of PET becomes faster and the nucleation density increases significantly with increasing Si O2 content. For PET and its nanocomposites thermally aged at 190 °C, the results of intrinsic viscosity, carboxyl content and tensile test show that the degradation rate of PET is reduced with the addition of a small content of Si O2, but the degradation rate increases with further addition of Si O2, owing to the dual effect of Si O2 on PET degradation.     

Synthesis, structural study and hydrolytic degradation of copolymer based on glycolic acid and bis-2-hydroxyethyl terephthalate

The current demand for environmentally degradable copolymers has initiated the use of novel degradable copolyesters. One of them is a copolyester based on poly(ethylene terephthalate-co-glycolic acid) (PET-GLA). The copolymer was synthesized by the melt reaction of bis-2-hydroxyethyl terephthalate (BHET) with glycolic acid (GLA) oligomers in the presence of Sb₂O₃ as a catalyst.Hydrolytic degradation of the copolymer was carried out in two buffered solutions at 45 °C: degradation was studied by incubating samples in powder form, in a concentrated solution from 30 to 150 days.The copolymer before and after degradation was characterized by means of different analytical techniques. ¹H and ¹³C NMR spectroscopy was used to confirm the incorporation of glycolide units in PET chains and to observe the structure and decomposition of the novel polyester. The thermal properties and morphology before and during the degradation were studied by scanning electron microscopy (SEM), differential scanning calorimetry (DSC) and thermogravimetric (TG) analysis for determining melting points as well as melting and decomposition temperatures of investigated copolyester.     

Real-time X-ray scattering study of thermal expansion of poly(butylene terephthalate)

Real-time x-ray scattering at elevated temperatures has been used to investigate the thermal expansion characteristics of poly(butylene terephthalate), PBT. Changes in the six lattice parameters of the α-form of PBT were obtained from wide-angle x-ray scattering over the temperature range from 35 to 215°C. The linear thermal expansion coefficients relating the unit cell parameters at temperature T to their values at 0°C are found to be The temperature dependence of both the long period and the lamellar thickness of semicrystalline PBT were determined from real-time small-angle x-ray scattering analysis of the one-dimensional electron density correlation function. The long period, lamellar thickness, and degree of crystallinity increase as the temperature increases. We find an average linear thermal expansion coefficient of the bulk material to be α_ave = 5.0 × 10⁻⁴°C⁻¹. © 1992 John Wiley & Sons, Inc.     

Kinetic study of the thermal degradation of high density polyethylene

The thermal degradation of high density polyethylene has been modelled by the random breakage of polymer bonds, using a set of population balance equations. A model was proposed in which the population balances were lumped into representative sizes so that the experimentally determined molecular weight distribution of the original polymer could be used as the initial condition. This model was then compared to two different cases of the unlumped population balance which assumed unimolecular initial distributions of 100 and 500 monomer units, respectively. The model that utilised the experimentally determined molecular weight distribution was found to best describe the experimental data. The model fits suggested a second mechanism in addition to random breakage at slow reaction rates.     

TSDC and DSC Study of Effects of Physical Aging on Polybutylene Terephthalate (PBT)

The impact of the physical aging process on the electrical and thermal properties of semicrystalline polybutylene terephthalate (PBT) was investigated by means of thermally stimulated depolarization currents (TSDC) and differential scanning calorimetry (DSC). The TSDC technique was used to study the relaxation modes of PBT in the temperature range ?50° to + 120°C. The obtained spectra revealed two peaks located at temperature maxima of 45° and 93°C. The peak appearing at 45°C corresponds to the dielectric manifestation of the glass transition phenomenon (α-relaxation). The aim of this work is to study the effect of physical aging on this relaxation. The recording of TSDC peaks of aged PBT at different temperatures for different times revealed a reduction in their intensities and their shift towards higher temperatures when the aging becomes significant. This result can be explained by the diminution of molecular chain mobility, which is directly related to the area under the peak representing the polarization of the sample. This result was confirmed by DSC measurements, which revealed the growth and the shift of the peak, which is superimposed on the jump of the heat capacity, located around 38°C and characteristic of the glass transition, towards higher temperatures where aging becomes significant.     

Hydrolytic degradation of copolymers based on l-lactic acid and bis-2-hydroxyethyl terephthalate

The current demand for environmentally degradable copolymers has led to the use of novel degradable copolyesters. A series of copolyesters based on bis-2-hydroxyethyl terephthalate and l-lactic acid oligomers were synthesized by melt polycondensation [Olewnik E, Czerwiński W, Nowaczyk J, Sepulchre M-O, Tessier M, Salhi S, et al. Synthesis and structural study of copolymers of l-lactic acid and bis(2-hydroxyethyl terephthalate). Eur Polym J, in press]. Hydrolytic degradation of copolymers containing 16.8-52.9 mole ratio of l-lactic acid units was carried out in two buffered solutions at two different temperatures: phosphate buffer solution (pH 7.40) at 45 °C and phosphate-citric buffer solution (pH 7.35) at 60 °C. Degradation of copolyesters was studied by incubating samples in powder form in a concentrated solution from 30 to 180 days.The copolymers were characterized by various analytical techniques. The thermal properties, morphology and structural changes during controlled hydrolysis were studied by scanning electron microscopy (SEM), differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA) for determining melting points, heats of melting and decomposition temperatures of investigated copolyesters. ¹H NMR spectroscopy was used to observe the decomposition of the polyesters.     

A modulated dsc study on the in situ polymerization of cyclic butylene terephthalate oligomers

The polymerization of a cyclic butylene terephthalate (CBT) oligomer was studied as a function of temperature (T=200 and 260°C, respectively) by modulated DSC (MDSC). The first heating was followed by cooling after various holding times (5, 15 and 30 min) prior to the second heating which ended always at T=260°C. This allowed us to study the crystallization and melting behavior of the resulting polybutylene terephthalate (PBT), as well. In contrary to the usual belief, the CBT polymerization is exothermic and the related process is superimposed to that of the CBT melting. The melting behavior of the PBT was affected by the polymerization mode (performed below or above the melting temperature of the PBT product) of the CBT. Annealing above the melting temperature of PBT yielded a product featuring double melting. This was attributed to the presence of crystallites with different degrees of perfection. The crystals perfection which occurred via recrystallization/remelting was manifested by a pronounced exothermic peak in the non-reversing trace.     

A comparative study on transreactions induced phase changes in blends of poly(trimethylene terephthalate) and poly(ethylene naphthalate) upon annealing

By using wide-angle X-ray diffraction (WAXD), thermal analysis, scanning and optical microscopy, and nuclear magnetic resonance (NMR) analyses, this study has demonstrated that blends of two semicrystalline polyesters, poly(trimethylene terephthalate) and poly(ethylene naphthalate) (PTT/PEN), were initially immiscible in as-blended state. The process of blend phase/morphology changes upon extended heating/annealing at elevated temperatures was monitored and probed. With reactions induced at heating/annealing at high temperatures (300°C) for long enough times, the original two phases quickly merged into a single phase. NMR analyses have shown that the products of the transreactions are identified as the random copolyesters (termed as EN-TT). From the NMR results, statistical analyses revealed that the average sequence lengths decreased upon heating, and the degree of chain randomness increased with time of heating at the fixed temperature. Upon extended heating, all PTT and PEN chains could be fully transformed into random copolymers of higher randomness with only a single but amorphous phase. Results are compared to another blend system comprised of PEN and a homologous polyester, PPT, of different structure. Influence of polyester structure on transreactions and phase homogenization process is analyzed.