Thermal and hydrolytic degradation of poly(1,4-cyclohexylenedimethylene terephthalate)

The kinetics of simultaneous thermal and hydrolytic degradation of poly(1,4-cyclohexylenedimethylene terephthalate) (PCHDT) were evaluated by using a 1.5-in.-diam. melt extruder (≈20/1 length/diameter ratio) as a reactor. The effects of extrusion temperature (295°-330°C), residence time (2.6–17.5 min), and moisture content (<0.001% to 0.2%) of the supply polymer on degradation were determined. The rate of degradation was measured in terms of the rate at which inherent viscosity (I.V.) decreased and the rate at which carboxyl endgroup concentration increased. The contributions of both thermal and hydrolytic degradation to the total degradation of PCHDT could be separated because the hydrolysis was rapid enough that it could be considered as occurring prior to thermal degradation. Thus, the hydrolysis merely adjusted the initial properties of the supply polymer, which was then subjected to thermal degradation. Equations were developed from an analysis of the kinetic data based on a random chain scission mechanism. The activation energies for decrease in I.V. and increase in carboxyl endgroup concentration of PCHDT from thermal degradation were determined as 33.5 and 41 kcal/mole, respectively.     

Thermal stability of polyethylene terephthalate

The kinetics of thermal and thermal-oxidative degradation of polyethylene terephthalate (PET) have been investigated as a function of melt temperature, melt residence time, melt environment, and drying environment. Rates of thermal and thermal-oxidative degradation were measured in terms of: weight loss of volatile degradation products, decreasing inherent viscosity, and increasing carboxyl end group concentration. Thermal-oxidative degradation was also investigated by Differential Scanning Calorimetry. Calorimetric results show that thermal-oxidative degradation of PET is an exothermic reaction, with an apparent activation energy of 117 kJ/mol. Melt temperature, melt residence time, melt environment, and drying environment have all been found to affect the degradation of PET. Analysis of inherent-viscosity kinetic data has been carried out, utilizing existing theories based on a random chain scission mechanism. Activation energies of 117 and 159 kJ/mol have been calculated for air-dried and vacuum dried samples respectively.     

Solid state polymerization of poly(ethylene terephthalate): Kinetic and property parameters

The kinetics of solid state polymerization of poly(ethylene terephthalate) (PET) have been investigated at a variety of conditions. Equations have been developed to describe the relationships of time, temperature, and final molecular weight for PET precursors prepared from specified catalyst and monomer systems. These studies show effects of: time and temperature of solid stating, moisture concentration, oxygen exposure, and nitrogen purge flow rate. Measurements of inherent viscosity, carboxyl end group concentration, melting point, residual acetaldehyde, and acetaldehyde generated during melting are used to monitor molecular weight, purity, and thermal stability of these solid stated resins.     

聚对苯二甲酸丙二醇酯的热性能研究

研究了聚对苯二甲酸丙二醇酯 (PTT) ,PET ,CDP在不同温度和时间下的特性粘数和端羧基含量的变化。结果表明 ,一定温度下 ,PTT熔体特性粘数随熔融时间的延长而下降 ,一定时间下 ,随温度的升高而下降。PTT端羧基含量随温度升高而增大 ,PTT的热稳定性较PET明显下降。     

Processing effects on poly(ethylene terephthalate) from bottle scraps

Processing of virgin and recycled poly(ethylene terephthalate) (PET) in a twin screw extruder evidences the degradative effect caused by thermal decomposition of poly(vinyl chloride) (PVC) and other impurities, e.g. adhesives, at the processing temperature. Lower melt viscosity and molecular weight, along with higher carboxylic end group concentration, were observed for recycled PET, the extent depending on PET purity. In an attempt to investigate the correlation between the kinetics of degradation phenomena and the level of thermomechanical stress, a novel dynamic method of evaluating thermal stability in processing conditions was developed. Such a method allows the achievement of long equivalent residence times while using lab-scale extruders. As a result of these experiments, PVC-rich recycled PET was shown to reach very low melt viscosity after less than 10 min in processing conditions, while virgin PET retained high viscosity even after 30 min.     

Processing characteristics of poly(ethylene terephthalate): hydrolytic and thermal degradation

The effects of poly(ethylene terephthalate) (PET) resin moisture content and temperature exposure have been investigated in terms of material changes resulting from the injection moulding process. Two resins with initial carboxyl contents of 10 µeq/g PET and 20 µeq/g PET have been analysed. Preforms processed at different resin moisture contents and processing temperatures of 280, 290 and 300 °C were evaluated in terms of carboxyl end‐group concentration using a titration method. Intrinsic viscosities of the performs were also measured by solution viscosity. Mathematical models describing the relationships of carboxyl end‐group concentration and intrinsic viscosity to the processing conditions were generated from the experimental data. Carboxyl end‐groups formed were compared for both resins and shown to be dependent on initial carboxyl content in the resin. Reducing the initial carboxyl content in the resin has been shown to increase its hydrolytic stability. The hydrolytic effect on the overall molecular weight drop was separated from the thermal/thermal‐oxidative degradation and shown to be dependent on both the processing temperature and the resin moisture content. © 2002 Society of Chemical Industry     

Thermal degradation of poly(butylene terephthalate)

The thermal degradation of poly(butylene terephthalate) between 240° and 280°C has been studied by measurements of intrinsic viscosity, carboxyl end groups and weight loss. A first-order mechanism of fission, followed by elimination of butadiene, is proposed. The values of the kinetic constant and activation energy are in good agreement with those obtained for simple esters and poly(ethylene terephthalate).     

聚酯端羧基控制的改进

从酯化和缩聚2个阶段分析了聚酯端羧基产生的原因。确定了工艺调整方案,通过提高酯化液位延长酯化停留时间来提高酯化率,降低缩聚反应温度尤其是终缩聚的温度减缓热降解反应,对降低产品端羧基值有一定效果。     

Quantification of thermal material degradation during the processing of biomedical thermoplastics

Three‐dimensional plotting, a melt‐based technique that involves the guided deposition of extruded filaments, is a promising method for the manufacture of thermoplastic scaffolds for tissue engineering. However, the polymer degrades during processing because of a prolonged residence time at an elevated temperature in the dispensing head before actual extrusion. This thermal degradation has been attributed to random chain scission; in this research, it has been quantified as a function of the residence time for a selection of polylactide‐based polymers. The utilized techniques include thermogravimetric analysis (overall mass loss), differential scanning calorimetry (glass‐transition, melting, and recrystallization temperatures), gel permeation chromatography (molecular mass), and inherent viscosity measurements. Experiments have shown that a static heating interval greater than 6 h is sufficient to destroy the molecular chain integrity of poly(l‐lactide) and poly(d,l‐lactide). Copolymers with poly(ε‐caprolactone) and poly(glycolic acid) are more resilient to thermal loading but are still severely affected. Overall, the differential scanning calorimetry results have been judged to be a good source of complementary data for the quantification of the degradation phenomenon, whereas inherent viscosity measurements have been confirmed to be related to the gel permeation chromatography results, which indicate shortening of the polymer chain. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

扩链聚对苯二甲酸丁二醇-co-聚己二酸丁二醇酯的合成及表征

采用1,4-丁二醇,对苯二甲酸二甲酯,己二酸合成了聚对苯二甲酸丁二醇-co-聚己二酸丁二醇酯(PBAT)。采用六亚甲基二异氰酸酯作为扩链剂合成了高分子质量的PBAT。研究了扩链反应时间,扩链剂用量对特性黏度的影响;反应温度,扩链剂用量,扩链反应时间对PBAT分子质量、端羧基值的影响。采用核磁共振及红外光谱对聚合物的结构进行了表征。研究结果表明六亚甲基二异氰酸酯可以显著提高PBAT的分子质量,扩链以后力学性能有明显的提高。     

Fabrication and characterization of poly(1,4-cyclohexanedimthylene terephthalate-co-1,4-cyclohxylenedimethylene 2,6-naphthalenedicarboxylate) (PCTN) copolyester film: A novel copolyester film with exceptional performances for next generation flexible electronic devices

A novel, semi-crystalline poly(1,4-cyclohexylenedimethylene terephthalate-co-1,4-cyclohexylene dimethylene 2,6-naphthalenedicarboxylate) (PCTN) copolyester was synthesized and successfully extruded using an extruder attached with T-die. The extruded sheet was uniaxially cold-drawn into film at 150°C, a temperature between glass transition temperature and melting temperature. The mechanical, thermal, thermo-mechanical, water barrier, and optical properties of developed film were characterized. Orientation of different phases was analyzed by X-ray diffraction. The actual chemical composition of PCTN copolyester was analyzed by nuclear magnetic resonance spectroscopy. Our results clearly indicated the thermal, dimensional stability, mechanical, and water barrier properties of PCTN films increased in a linear trend with draw ratio. It was also found that PCTN film has better water barrier property compared to conventional poly(ethylene terephthalate) (PET) and poly(ethylene 2,6-naphthalate) (PEN) films. Based on the exceptional performance properties, novel PCTN film may find a strong position as a substrate for next generation flexible electronics among various performance materials.     

Effect of alkali on filaments of poly(ethylene terephthalate) and its copolyesters

The alkali hydrolysis of poly(ethylene terephthalate), anionic copolymer of poly(ethylene terephthalate), and block copolymer of poly(ethylene terephthalate)–poly(ethylene glycol) is investigated under a variety of conditions of alkali concentration in aqueous bath, additives, time, and temperature. Measurements of loss in weight, linear density, breaking load, tenacity, elongation to break apart from intrinsic viscosity, fiber density, COOH-end group content, diameter of filaments, and scanning electron micrographs have been analyzed to identify the differences in the action of alkali on these polymer materials.     

聚对苯二甲酸丙二酯聚合工艺的研究Ⅰ.树脂合成和性能表征

以对苯二甲酸二甲酯和 1 ,3-丙二醇为原料合成聚对苯二甲酸丙二酯 (PTT) ,重点研究了原料配比、缩聚温度、催化剂用量、稳定剂用量对聚合物粘度和端羧基含量的影响规律。结果表明 ,温度对聚合物性能影响最大 ,其它 3个因素的影响较小。     

Study on degradation reactions in polyethylene terephthalate containing 5‐sulpho isophthalyl moieties

Kinetics of thermal degradation occurring on polyester containing cationic dyeable comonomer units viz. 5‐sulphoisophthalate moieties are studied by measurement of changes in intrinsic viscosity and carboxyl values on the polymer after subjecting the polymer chips to temperatures in the range 275–285°C for different residence times ranging from 5 to 60 min and comparing with the homopolymer. The activation energy values for degradation are estimated from the kinetic data. Mechanical properties of the textured yarns produced from the partially oriented yarns (POY) spun under different residence times are measured. Yarn produced with higher residence time has poor mechanical properties. The SEM images of the POY show presence of particles at the surface of the yarn due to polymer degradation. The size of the particles as seen on the surface increase with increase of retention time. Addition of thermal stabilizer helps in controlling the thermal degradation. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

不同熔融混炼条件下PET的降解行为和结晶行为

采用不同预处理条件对聚对苯二甲酸乙二醇酯（PET）切片进行熔融混炼,考察了不同熔融混炼条件下PET的降解行为和结晶行为。结果表明,不同条件的熔融混炼过程均导致PET降解,而降解速率和样品含水率密切相关;PET的降解不仅导致其结晶速率提高,也将导致其球晶晶片厚度增加和结晶度增大;PET的结晶峰值温度（Tcp）、结晶起始温度（Tonset）和结晶结束温度（Tendset）与其特性黏度\[η\]之间存在相关关系,表现为\[η\]越小,Tcp越高,结晶速率越快。     

Pyrolysis and combustion of polyester. I. Thermochemistry of poly(1,4-cyclohexylene dimethylene terephthalate) treated with selected phosphorus- and halogen-containing flame retardants

A series of poly(1,4-cyclohexylene dimethylene terephthalate) (PCHDT) fabrics treated with selected phosphorus- and halogen-containing flame retardants has been studied by static oxygen bomb calorimetry. The amount of heat evolved when these fabrics are burned in the open atmosphere has been determined indirectly using calculations based on Hess' law of summation. This heat evolution when corrected for contributions due to burning of the flame retardant appeared to correlate with the efficiency of the flame retardant treatment and was interpretable in terms of mechanisms of flame retardant action. Also, this technique has been applied to blends containing polyester.     

The production of glass fiber-reinforced poly(butylene terephthalate) on a continuous kneader

In poly(butylene terephthalate) based compositions, thermal degradation of the polymer matrix during processing has to be minimized to achieve quality products. Experience has shown a temperature-residence time relationship, indicating that for mixing systems with high product temperatures, the residence time of the product has to be reduced to avoid excessive thermal degradation. The power density of the mixing system is related to the specific energy input and the residence time of the product. From rheology, the power density is also known for a simple shear deformation which can thus be used to characterize the shear intensity of a particular mixing process. Comparing two different mixing systems by their power density provides us with a qualitative better understanding why higher shear is permitted with lower residence time. From theoretical considerations it was found that for a temperature-sensitive product, like PBT, the power density in the mixing operation can be further raised, taking into account that with shorter residence time a higher product temperature is permitted. Production-scale test work was carried out on a 200 mm screw-diameter continuous kneader to investigate the effect of running conditions and screw design on the thermal degradation of two different types of PBT. Results have shown that for the high-viscosity PBT a linear relationship exists between product temperature and the viscosity retained upon compounding. In a two-stage kneader only minor thermal degradation is encountered in the melting section, but conditions become critical in the mixing stage due to the viscosity increase after introducing the glass fibers to the melt. A new feature in compounding thermodegradable products is the addition of unmolten polymer into the mixing stage of the kneader since this leads to a reduction in the product end temperature and, consequently, thermal degradation of the matrix material. The limited results obtained so far indicate that an optimum exists as to the amount of pellets added. At a 15 percent level the product temperature was reduced by 20°C as compared to 10°C at 20 percent. An energy balance carried out on the continuous kneader indicates that because of the low melt viscosity approximately 30 percent of the energy put into the product in the melting section of the kneader originates from external heating. A rough comparison shows that the power density of a continuous kneader is twice that of a single-screw extruder designed for compounding PBT, but, can be tolerated because of the considerably lower residence time in the former mixing system.     

Hydrolytic degradation of poly(ethylene terephthalate)

Molecular weight is an important factor in the processing of polymer materials, and it should be well controlled to obtain desired physical properties in final products for end‐use applications. Degradation processes of all kinds, including hydrolytic, thermal, and oxidative degradations, cause chain scission in macromolecules and a reduction in molecular weight. The main purpose of this research is to illustrate the importance of degradation in the drying of poly(ethylene terephthalate) (PET) before processing and the loss of weight and mechanical properties in textile materials during washing. Several techniques were used to investigate the hydrolytic degradation of PET and its effect on changes in molecular weight. Hydrolytic conditions were used to expose fiber‐grade PET chips in water at 85°C for different periods of time. Solution viscometry and end‐group analysis were used as the main methods for determining the extent of degradation. The experimental results show that PET is susceptible to hydrolysis. Also, we that as the time of retention in hydrolytic condition increased, the molecular weight decreases, but the rate of chain cleavage decreased to some extent, at which point there was no more sensible degradation. The obtained moisture content data confirmed the end‐group analysis and viscometry results. Predictive analytical relationships for the estimation of the extent of degradation based on solution viscosity and end‐group analysis are presented. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 103: 2304–2309, 2007     

Synthesis of polyether-based block copolymers based on poly(propylene oxide) and terephthalates

Poly(propylene oxide) (PPO) is a low reactive telechelic polyether and the synthesis of high molecular weight poly(propylene oxide)-based block copolymers was studied. The poly(propylene oxide) used was end capped with 20 wt % ethylene oxide and had a molecular weight of 2300 g/mol (ultra-low monol PEO-b-PPO-b-PEO). The type of terephthalic acid based precursors was varied: terephthalic acid, dimethyl terephthalate, diphenyl terephthalate, di(trifluoro ethyl) terephthalate, di(p-nitrophenyl) terephthalate) and terephthalic acid chloride. High molecular weight poly(propylene oxide) based segmented block copolymers were obtained with diphenyl terephthalate (inherent viscosity: 1.6 dl/g).The synthesis of polyether(ester-amide)s comprising PPO and isophthalamide-based segments was also studied by varying the polymerization temperature and time. High molecular weight poly(propylene oxide) block copolymers could be obtained if the reaction was carried out for 2 h at 250 °C under vacuum. Higher temperatures (280 °C) and longer times result in lower inherent viscosities, probably due to degradation of the polyether.     

改性共聚酯的化学结构及热降解性能

在5 L聚合装置上,成功合成了一系列用间苯二甲酸乙二醇酯-5-磺酸钠(SIPE)和聚乙二醇(PEG)改性的共聚酯(MECDP)。核磁氢谱(1H-NMR)的测试结果表明:聚合物大分子中的对苯二甲酸(PTA)、PEG、SIPE的摩尔比与其投料比基本相符;共聚酯分子链的化学结构,与设想的分子链结构较好地吻合。热重分析仪(TGA)试验结果表明:在氮气和空气的氛围里,热降解温度(T)d均随着PEG质量分数的增加而下降;在空气氛围里的热降解,比在氮气氛围内的热降解更容易发生;在氮气氛围里的TGA曲线,只有一个热失重平台,而在空气氛围里的TGA曲线,有两个热失重平台。特性黏度变化的测试结果表明:PEG的质量分数越高,干燥温度越高,干燥时间越长,共聚酯的特性黏度值变得越小。