Molecular and structural analysis of epoxide‐modified recycled poly(ethylene terephthalate) from rheological data

A multifunctional epoxide chain extender (ADR4370S) was used to increase the molecular weight of recycled poly(ethylene terephthalate) (R‐PET). The extension processing was carried out by melt mixing reaction. The effects of ADR4370S content on the molecular structure [molecular weight, molecular weight distributions (MWDs), branching, and gel‐like structures] of modified R‐PET were rheologically investigated. The results showed that the complex and apparent viscosity of the modified R‐PET were larger than those of unmodified one. The solid‐like behavior of R‐PET was enhanced after the reactive modification. The increments of balancing torque, reaction peak, and shear‐thinning behavior became more pronounced by increasing the concentration of ADR4370S. Reactive modification was characterized by the presence of long‐chain branching resulted in a wider MWD. Modified Cole–Cole plots demonstrated a shift toward higher storage modulus values at a given loss modulus value for the modified R‐PET samples. High concentration of ADR4370S (>1.5 wt%) resulted in a polymeric structure near the sol–gel transition point whose linear viscoelastic properties obeyed scaling law. The relaxation time was prolonged with the amount of ADR4370S increase. The decrease in the melt point and crystallization temperature of the modified R‐PET was correlated to the presence of chain branching. POLYM. ENG. SCI., 2012. © 2012 Society of Plastics Engineers     

Synthesis and characterization of poly(L‐lactic acid)‐b‐poly(ethylene terephthalate‐co‐sebacate)‐b‐poly(L‐lactic acid) copolyesters

Random copolyester namely, poly(ethylene terephthalate‐co‐sebacate) (PETS), with relatively lower molecular weight was first synthesized, and then it was used as a macromonomer to initiate ring‐opening polymerization of l ‐lactide. ¹H NMR quantified composition and structure of triblock copolyesters [poly(l ‐lactic acid)‐b‐poly(ethylene terephthalate‐co‐sebacate)‐b‐poly(l ‐lactic acid)] (PLLA‐PETS‐PLLA). Molecular weights of copolyesters were also estimated from NMR spectra, and confirmed by GPC. Copolyesters exhibited different solubilities according to the actual content of PLLA units in the main chain. Copolymerization effected melting behaviors significantly because of the incorporation of PETS and PLLA blocks. Crystalline morphology showed a special pattern for specimen with certain composition. It was obvious that copolyesters with more content of aromatic units of PET exhibited increased values in both of stress and modulus in tensile test. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2007     

Chain extension behavior and thermo‐mechanical properties of polyamide 6 chemically modified with 1,1′‐carbonyl‐bis‐caprolactam

A chain‐extender based on 1,1′‐Carbonyl‐Bis‐Caprolactam (CBC) was melt compounded with a commercial Polyamide 6 (PA6) by using a twin screw extruder. Rheological, thermal, and mechanical tests were performed on the resulting materials to evaluate the chain extension capability of CBC. Rheological tests on the compounded pellets and relative viscosity measurements on solubilized samples evidenced an increase of the viscosity values with the chain‐extender amount, while the opposite trend was determined increasing the high temperature residence time. Terminal group analysis confirmed the increase of the molecular weight with the CBC content and highlighted a preferential reactivity of the chain‐extender with aminic end groups. Differential scanning calorimetry (DSC) tests showed how both melting and relative crystallinity of the up‐graded samples decreased with the CBC amount. Elastic and yield properties of chain‐extended PA6 were similar to those of neat PA6 grades at different molecular weight, while crystallinity drop due to chain extension was responsible of an increase of the strain at break values. POLYM. ENG. SCI., 54:158–165, 2014. © 2013 Society of Plastics Engineers     

Solid‐state polymerization of melt‐spun poly(ethylene terephthalate) fibers and their tensile properties

The production of high modulus and high strength poly(ethylene terephthalate) fibers was examined by using commercially available melt‐spun fibers with normal molecular weight (intrinsic viscosity = 0.6 dL/g). First, molecular weight of as‐spun fibers was increased up to 2.20 dL/g by a solid‐state polymerization, keeping the original shape of as‐spun fibers. Second, the polymerized as‐spun fibers were drawn by a conventional tensile drawing. The achieved tensile modulus and strength of as‐drawn fibers (without heat setting) were 20.0 and 1.1 GPa, respectively. A heat setting was carried out for the as‐drawn fibers. Tensile properties of the treated fibers were greatly affected by the condition of the heat setting. This was related to the increase of sample crystallinity and molecular degradation during the treatments. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 103: 1791–1797, 2007     

Synthesis and characterization of a novel poly(ester‐urethane) containing short lactate sequences and PEG moieties

A novel poly(ester‐urethane) with tailor‐made structure was prepared by using lactic acid (LA) as starting material through a combination of two facile common reactions. First, a diol was prepared via the esterification between LA and poly(ethylene glycol) (PEG) with low molecular weight. Subsequently, the poly(ester‐urethane) was synthesized through the addition polymerization of the LA‐based diol and toluene 2,4‐diisocyanate with 1,4‐butanediol as chain extender. The structure, morphology, and properties of intermediate and the poly(ester‐urethane) were analyzed with Fourier transform infrared spectroscopy, proton nuclear magnetic resonance, gel permeation chromatography (GPC), X‐ray diffraction, differential scanning calorimetry, polarizing optical microscopy, and thermogravimetric analysis. The results indicated that the intermediate was a diol of conjugating quite short lactate sequences with PEG oligomer, and the structure of the poly(ester‐urethane) was as expected. The thermal transition, thermal decomposition temperature, and crystallinity of the polymer samples depended on the molecular size of PEG. In vitro degradation property of the poly(ester‐urethane) also relied on the molecular weight of PEG. The weight loss percentages varied from 11 to 36% after 12‐days immersing in phosphate‐buffer saline at 37°C. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

Properties of high‐speed spun high molecular weight poly(ethylene terephthalate) filaments

High‐speed spinning of high molecular weight poly(ethylene terephthalate) (PET) having an intrinsic viscosity of 0.98 dL/g was performed at the take‐up velocity range of 2.5–5.5 km/min. The structure of the as‐spun filaments was analyzed by density, birefringence, WAXS, DSC, boiling water shrinkage, and tensile properties. Stress‐induced crystallization takes place above 3 km/min, which is confirmed by the steep increase in density, the growth of the crystal size, melting point increase, and the decrease in boiling water shrinkage. The plot of crystallinity versus birefringence shows that crystallinity increases drastically after birefringence reaches the value of about 0.075. A comparison with the data of other researchers will clearly present the effects of molecular weight on the properties of PET filaments spun at high speed, for example, the take‐up velocity range of the steep increase in density for high molecular weight PET is lower than that for low molecular weight PET by about 1 km/min. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 71: 1283–1291, 1999     

Chain extension reaction in solid‐state polymerization of recycled PET: The influence of 2,2′‐bis‐2‐oxazoline and pyromellitic anhydride

Conventional and chain extended‐modified solid‐state polymerization (SSP) of postconsumer poly(ethylene terephthalate) (PET) from beverage bottles was investigated. SSP was carried out at several temperatures, reaction times, and 2,2′‐bis‐2‐oxazoline (OXZ) or pyromellitic anhydride (ANP) concentrations. The OXZ was added by impregnation with chloroform or acetone solution. Higher molecular weights were reached when the reaction was carried out with OXZ, resulting in bimodal distribution. The molecular weights of the flakes reacted at 230°C for 4 h were 85,000, 95,000, and 100,000 for samples impregnated with 0, 0.5, and 1.25 wt % OXZ solution, respectively. In the case of reactions with ANP, branched chains were obtained. The thermal and thermal‐mechanical‐dynamic properties of these high‐molecular‐weight recycled PET were determined. For OXZ‐reacted samples, the reduction of crystallinity was observed as the reaction time was increased, becoming evident the destruction of the crystalline phase. The chain extended samples did not show changes in thermal relaxations or thermal degradation behavior. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Chain extenders for polyester. II. Reactivities of carboxyl-addition-type chain extenders; bis cyclic-imino-ethers

The reaction behavior of such bis cyclic-imino-ethers as 2, 2′-bis(2-oxazoline), which had been proved in the previous paper to be an effective chain extender to couple carboxyl terminals of linear polyesters through addition reaction, has been studied to evaluate their practical applicability as the chain extenders for poly(ethylene terephthalate) and poly(butylene terephthalate). It has been observed that a wide range of excess use of 2,2′-bis(2-oxazoline) resulted in polyesters of almost similar molecular weight. In addition, when excess amounts of the chain extender were added and the reaction conditions were fixed, the ratio of the coupled carboxyl terminals to the initial carboxyl terminals became constant regardless of the initial molecular weight and carboxyl content (CV). The results indicate that the chain-extended polyesters possess predetermined molecular weight and CV, both of which depend only on the molecular weight and CV of the initial polymers, and not on the amount of the chain extender added.     

Structural investigations of poly(ethylene terephthalate)‐graft‐polystyrene copolymer films

Structural investigations of poly(ethylene terephthalate)‐graft‐polystyrene (PET‐g‐PS) films prepared by radiation‐induced grafting of styrene onto commercial poly(ethylene terephthalate) (PET) films were carried out by FTIR, X‐ray diffraction (XRD), and differential scanning calorimetry (DSC). The variation in the degree of crystallinity and the thermal characteristics of PET films was correlated with the amount of polystyrene grafted therein (i.e., the degree of grafting). The heat of melting was found to be a function of PET crystalline fraction in the grafted films. The grafting is found to take place by incorporation of amorphous polystyrene grafts in the entire noncrystalline (amorphous) region of the PET films and at the surface of the crystallites. This results in a decrease in the degree of crystallinity with the increase in the degree of grafting, attributed to the dilution of PET crystalline structure with the amorphous polystyrene, without almost any disruption in the inherent crystallinity. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 84: 1949–1955, 2002; DOI 10.1002/app.10515     

Poly(ethylene terephthalate)/polypropylene microfibrillar composites. III. Structural development of poly(ethylene terephthalate) microfibers

Poly(ethylene terephthalate) was extruded, solid‐state‐drawn, and annealed to simulate the structure of poly(ethylene terephthalate) microfibers in a poly(ethylene terephthalate)/polypropylene blend. Differential scanning calorimetry and wide‐angle X‐ray scattering analyses were conducted to study the structural development of the poly(ethylene terephthalate) extrudates at different processing stages. The as‐extruded extrudate had a low crystallinity (～ 10%) and a generally random texture. After cold drawing, the extrudate exhibited a strong molecular alignment along the drawing direction, and there was a crystallinity gain of about 25% that was generally independent of the strain rates used (0.0167–1.67 s^?1). 2θ scans showed that the strain‐induced crystals were less distinctive than those from melt crystallization. During drawing above the glass‐transition temperature, the structural development was more dependent on the strain rate. At low strain rates, the extrudate was in a state of flow drawing. The resultant crystallinity hardly changed, and the texture remained generally random. At high strain rates, strain‐induced crystallization occurred, and the crystallinity gain was similar to that in cold drawing. Thermally agitated short‐range diffusion of the oriented crystalline molecules was possible, and the resultant crystal structure became more comparable to that from melt crystallization. Annealing around 200°C further increased the crystallinity of the drawn extrudates but had little effect on the texture. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 104: 137–146, 2007     

Transesterification reactions in triphenyl phosphite additivated‐poly(ethylene terephthalate)/poly(ethylene naphthalate) blends

The occurrence of transesterification reactions in poly(ethylene terephthalate) (PET)/poly(ethylene naphthalate) (PEN) blends prepared in presence of triphenyl phosphite (TPP) was investigated. When PEN was processed with TPP, which is a known chain extender for PET, chain extension reactions also took place. Torqueprocessing time curves obtained during preparation of 75/25 PET/PEN blends containing TPP, showed a build‐up profile followed by a fast decrease that was interpreted as chain extension between blend components and degradation due to phosphite residues formation, respectively. Although transesterification inhibition was expected, this type of reaction was not suppressed by TPP.     

Effect of cyclotrimerization of bisphenol‐A dicyanate monomer on poly(ethylene terephthalate) chain extension

The engineering application of poly(ethylene terephthalate) (PET) was limited by its low melt viscosity and strength. Numerous chain extenders were used to enlarge the molecular weight so as to overcome these shortcomings including bisphenol‐A dicyanate (BADCy), which was proven effective in one of our previous work. It was considered that tri‐mer of BADCy through cyclotrimerization might strengthen the effectiveness in chain extender for PET, and the effect of BADCy tri‐mer was studied in this work. With increasing the cyclotrimerization reaction temperature of BADCy monomer, the conversion to tri‐mers was increased. With a fraction of BADCy tri‐mer in the chain extender, the modified PET exhibited higher melt torque, intrinsic viscosity, melt modulus, and melt viscosity than those modified by BADCy monomer alone. BADCy tri‐mer had a positive effect on the chain extension of PET. However, the fraction of tri‐mers in the monomer/tri‐mer mixture should be limited to a certain value; otherwise, the chain extension would be weakened. POLYM. ENG. SCI., 2011. © 2011 Society of Plastics Engineers     

Radiation‐induced crosslinking of acetylene‐impregnated polyesters. II. Effects of preirradiation crystallinity,molecular structure,and postirradiation crosslinking on mechanical properties

Electron beam‐irradiated crosslinking has been studied in a series of acetylene‐impregnated polyesters and amorphous copolyesters, including poly(ethylene terephthalate) (PET), poly(butylene terephthalate) (PBT), poly(cyclohexane dimethylene terephthalate) (PCDT), and poly(cyclohexane dimethylene terephthalate‐co‐ethylene terephthalate) (P(CDT‐co‐ET)) having 29 and 60 wt % ethylene terephthalate (ET). The extent of crosslinking was observed by gel fraction measurements and was found to be significantly influenced by the aliphatic chain content of the polyesters (PET < PBT < PCDT). In addition, as the preirradiation crystallinity of the polyesters was reduced, the extent of acetylene‐enhanced crosslinking was greatly raised. Decreases in the postirradiation crystalline melting temperature and degree of crystallinity were observed in all the polyesters, using differential scanning calorimetry measurements. Particularly significant findings have been the shift in the glass‐transition temperatures (Tg) to higher temperatures and the decrease in loss tangents at higher temperatures, both of which confirm that crosslinking has taken place. The storage moduli (E′) in the rubbery plateau region of PCDT and P(CDT‐co‐ET) were significantly affected by irradiation dose. Increased network tightness in postirradiated PBT and PCDT films was also inferred from melt‐rheology measurements, in which stress relaxed more slowly following a stepped strain. Improvements in the mechanical properties of the irradiated polyesters and copolyesters were clearly evidenced by the increased modulus at higher temperatures, observed using dynamic mechanical thermal analysis and melt‐rheology methods. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 100: 4476–4490, 2006     

Copolymers based on poly(butylene terephthalate) and polycaprolactone‐block‐polydimethylsiloxane‐block‐polycaprolactone

A series of novel thermoplastic elastomers, based on poly(butylene terephthalate) (PBT) and polycaprolactone‐block‐polydimethylsiloxane‐block‐polycaprolactone (PCL‐PDMS‐PCL), with various mass fractions, were synthesized through melt polycondensation. In the synthesis of the poly(ester‐siloxane)s, the PCL blocks served as a compatibilizer for the non‐polar PDMS blocks and the polar comonomers dimethyl terephthalate and 1,4‐butanediol. The introduction of PCL‐PDMS‐PCL soft segments resulted in an improvement of the miscibility of the reaction mixture and therefore in higher molecular weight polymers. The content of hard PBT segments in the polymer chains was varied from 10 to 80 mass%. The degree of crystallinity of the poly(ester‐siloxane)s was determined using differential scanning calorimetry and wide‐angle X‐ray scattering. The introduction of PCL‐PDMS‐PCL soft segments into the polymer main chains reduced the crystallinity of the hard segments and altered related properties such as melting temperature and storage modulus, and also modified the surface properties. The thermal stability of the poly(ester‐siloxane)s was higher than that of the PBT homopolymer. The inclusion of the siloxane prepolymer with terminal PCL into the macromolecular chains increased the molecular weight of the copolymers, the homogeneity of the samples in terms of composition and structure and the thermal stability. It also resulted in mechanical properties which could be tailored. Copyright © 2010 Society of Chemical Industry     

Preparation and properties of microcapsule with EVA core‐PU shell structure

Microcapsule with poly(ethylene‐co‐vinylacetate) (EVA) core‐polyurethane (PU) shell structure was synthesized by interfacial polymerization in aqueous polyol dispersion with ethylene diamine as the chain extender of toluene diisocyanate in poly(vinyl alcohol) aqueous solution as the stabilizing agent. The effects of polyol constituent on the average particle size and distributions, morphologies, color strength, and friction fastness of core‐shell particles were investigated to design microcapsule. The friction fastness of printed fabrics with EVA core‐PU shell microcapsules became the increase to 4–5 grades. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 103: 893–902, 2007     

Chain extension of recycled poly(ethylene terephthalate) with 2,2′‐(1,4‐phenylene)bis(2‐oxazoline)

The present work provides improved recycled high molecular weight poly(ethylene terephthalate) (PET) by chain extension using 2,2′‐(1,4‐phenylene)bis(2‐oxazoline) (PBO) as the chain extender. PBO is a very reactive compound toward macromolecules containing carboxyl end groups but not hydroxyl end groups. In the case of PET, where both species are present, for even better results, phthalic anhydride (PA) was added in the initial sample, before the addition of PBO. With this technique, we succeeded in increasing the carboxyl groups by reacting PA with the hydroxyl terminals of the starting polymer. From this modification of the initial PET sample, PBO was proved an even more effective chain extender. So, starting from a recycled PET with intrinsic viscosity [η] = 0.78, which would be [η] = 0.69 after the aforementioned treatment without a chain extender or M̄_n = 19,800, we prepared a PET grade having [η] = 0.85 or M̄_n = 25,600 within about 5 min. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 77: 2206–2211, 2000     

Effect of structure modification on rheological properties of biodegradable poly(ester‐urethane)

Biodegradable lactic acid based poly(ester‐urethanes) (PEU) were polymerized and their structure and rheological properties were characterized. The polymerization process comprised two steps: lactic acid monomer was oligomerized to low molecular weight prepolymer, and this was then linked to high molecular weight PEU with chain extender, 1,6‐hexamethylene diisocyanate. The properties of PEU were modified by varying the amount of chain extender from 1.05:1 to 1.35:1 (NCO/OH ratio). The modification was mostly seen in the molecular weight distribution of the polymers, which was broadened from 2.2 to 3.5 as the amount of chain extender was increased. The telechelicity of the prepolymer was found to play an essential role in successful linking of the prepolymer units. In addition, the rheological properties of poly(ester‐urethane) were determined with capillary and dynamic rheometers. All PEU samples were pseudoplastic and broadening of their molecular weight distribution was accompanied by increased viscosity and complex viscosity at low shear rates and increased shear thinning. The temperature dependency of the measurement was pronounced. Rheological measurements also showed that PEU starts to degrade at 100°C and further rise in temperature increases the rate of degradation significantly.     

Molecular structures and physical properties of heat‐drawn conjugate fibers

As‐spun poly(trimethylene terephthalate) (PTT)/poly(ethylene terephthalate) (PET) side‐by‐side conjugate fibers were drawn to investigate the effects of drawing conditions on structure development and physical properties. Effects of draw ratio and heat‐set temperature were observed. In the state of an as‐spun fiber, the molecular orientation of PTT was higher than PET, whereas PET molecular orientation increased remarkably over PTT with increasing draw ratio. Crimp contraction increased sharply at a draw ratio over 2.0, where the crystalline structure of the PET developed sufficiently. A heat‐set temperature of at least 140°C was required to develop sufficient crimp contraction. The crystallinity and orientation of the PET were attributed mainly to the crimp contraction of the drawn fiber. POLYM. ENG. SCI., 2011. © 2010 Society of Plastics Engineers     

Preparation and characterization of high‐molecular‐weight poly(l‐lactic acid) by chain‐extending reaction with phosphites

Poly(l ‐lactic acid) (PLLA) of high molecular weight was prepared by a chain‐extending reaction in a microcompounder. Phosphites were used as chain extenders to increase the molecular weight of the PLLA prepolymer, which was prepared by the bulk polycondensation of l‐lactic acid. The effects of the amount of phosphite, the temperature, and the screw speed on the torque of the PLLA melt were studied. Under the optimal conditions, the molecular weight of PLLA increased from 62,100 to 126,000 g/mol. The chemical structure and crystallinity of PLLA were characterized by Fourier transform infrared spectroscopy, ¹H‐NMR and ¹³C‐NMR, differential scanning calorimetry, and X‐ray diffraction. The mechanical properties of PLLA were measured. The results indicate that triphenyl phosphite (TPPi) was an effective chain extender for PLLA. The role of the TPPi in chain extending is suggested to be an esterification‐promotion agent. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012     

Degradation of crosslinked poly(ester‐urethanes) elastomers in distilled water: Influence of hard segment

Polyurethane elastomers are frequently used in wet conditions. Crosslinked polyurethanes based on poly(ethylene adipate) diol, 4,4′‐diphenylmethane diisocyanate, 1,6 hexane diisocyanate—with different hard‐segment compositions but with the same molecular weight soft segment—were degraded in distilled water at 37°C, in a specific environment; in the dark without exposure to enzymatic conditions and under the continuous circulation of water. The incubation of polymer samples took place over a period of maximum 30 days. The degradation process was evaluated by the changes in mechanical properties and surface relief observed by optical microscopy. The changes in hydrogen bonding were collected through attenuated total reflectance infrared (ATR‐FTIR) spectroscopy which indicated that aliphatic diisocyanates allow for a better formation of hydrogen bonds. The mechanical properties of the degraded films show that the crosslinked polyurethanes containing aromatic diisocyanate suffer a decrease in tensile strength between 33 and 56% depending on the chain extender and hard segment content. The hydrolytic degradation behavior of crosslinked polyurethanes was found to be dependent on the diisocyanate and chain extender structure, as well as on the hard segment content and chemical crosslinks. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012