Melt rheology of poly(lactic acid): Consequences of blending chain architectures

The rheology of blends of linear and branched poly(lactic acid) (PLA) architectures is comprehensively investigated. Measurement of the melt rheological properties of PLA is complicated by degradation effects but the addition of 0.35 wt% tris(nonylphenyl) phosphite (TNPP) provides excellent stabilization over a range of temperatures. Master curves of dynamic viscosity constructed using time‐temperature superposition show significant dispersion for unstabilized samples; this behavior is accompanied by a loss of molecular weight. TNPP stabilized samples show excellent superposition throughout the entire frequency range and minimal loss in molecular weight. For the linear architecture, the Cox‐Merz rule is valid for a large range of shear rates and frequencies. The branched architecture deviates from the Cox‐Merz equality and blends show intermediate behavior. Both the zero shear viscosity and the elasticity (as measured by the recoverable shear compliance) Increase with increasing branched content. The viscosities of both the unstabilized samples and the TNPP stabilized samples roughly obey a log additivity mixing rule. The recoverable shear compliance is monotonic in blend composition and a mixing rule for this property is also presented. For the linear chain, the compliance is independent of temperature but this behavior is apparently lost for the branched and blended materials. Tensile and thermal properties of the blends are also measured and found to be roughly equal within the statistical error of the experiments. The results suggest that excellent control over rheological behavior of PLA is possible through blending chain architectures without compromising mechanical properties.     

Synthesis and characterization of soluble poly(arylene ether ketone)s with high glass transition temperature based on 3,6‐bi(4‐fluorobenzoyl)‐N‐alkylcarbazole

3,6‐bi(4‐fluorobenzoyl)‐N‐methylcarbazole and 3,6‐bi(4‐fluorobenzoyl)‐N‐ethylcarbazole were synthesized and used to prepare poly(arylene ether ketone)s (PAEKs) with high glass transition temperatures (T_g) and good solubility. High molecular weight amorphous PAEKs were prepared from these two difluoroketones with hydroquinone, phenolphthalein, 9,9‐bis(4‐hydroxyphenyl)fluorene and 4‐(4‐hydroxylphenyl)‐2,3‐phthalazin‐1‐one, respectively. All these polymers presented high thermal stability with glass transition temperatures being in the range 239–303 °C and a 5% thermal weight loss temperature above 460 °C. Compared with the T_g of phenolphthalein‐based PAEK (PEK‐C), fluorene‐based PAEK (BFEK) and phthalazinone‐based PAEK (DPEK) not containing a carbazole unit, these polymers presented a 30–50 °C increase in T_g. Meanwhile, PAEKs prepared from N‐ethylcarbazole difluoroketone showed good solubility in ordinary organic solvents, and all polymers exhibited excellent resistance to hydrochloric acid (36.5 wt%) and sodium hydroxide (50 wt%) solutions. In particular, phthalazinone‐based PAEK bearing N‐ethylcarbazole afforded simultaneously a T_g of 301 °C with good solubility. Tensile tests of films showed that these polymers have desirable mechanical properties. The carbazole‐based difluoroketones play an important role in preparing soluble PAEKs with high T_g by coordinating the relationship between chain rigidity resulting from the carbazole unit and chain distance from the side alkyl. © 2014 Society of Chemical Industry     

Synthesis and properties of copolymers of poly(ether ketone ketone) and poly(ether amide ether amide ether ketone ketone)

Poly(aryl ether ketone)s (PAEKs) are a class of high‐performance engineering thermoplastics known for their excellent combination of chemical, physical and mechanical properties, and the synthesis of semicrystalline PAEKs with increased glass transition temperatures (T_g) is of much interest. In the work reported, a series of novel copolymers of poly(ether ketone ketone) (PEKK) and poly(ether amide ether amide ether ketone ketone) were synthesized by electrophilic solution polycondensation of terephthaloyl chloride with a mixture of diphenyl ether and N,N′‐bis(4‐phenoxybenzoyl)‐4,4′‐diaminodiphenyl ether (BPBDAE) under mild conditions. The copolymers obtained were characterized using various physicochemical techniques. The copolymers with 10–35 mol% BPBDAE are semicrystalline and have markedly increased T_g over commercially available poly(ether ether ketone) and PEKK due to the incorporation of amide linkages in the main chain. The copolymers with 30–35 mol% BPBDAE not only have high T_g of 178–186 °C, but also moderate melting temperatures of 335–339 °C, having good potential for melt processing. The copolymers with 30–35 mol% BPBDAE have tensile strengths of 102.4–103.8 MPa, Young's moduli of 2.33–2.45 GPa and elongations at break of 11.7–13.2%, and exhibit high thermal stability and good resistance to organic solvents. Copyright © 2010 Society of Chemical Industry     

Crystallization,rheological behavior and mechanical properties of poly(vinylidene fluoride) composites containing graphitic fillers: a comparative study

The effect of three kinds of graphitic fillers with distinct morphologies, natural graphite sheets (NGs), chemically reduced graphite oxide sheets (CRGs) and thermally reduced graphite oxide sheets (TRGs), on the crystallization, rheological behavior and mechanical properties of poly(vinylidene fluoride) (PVDF)‐based composites has been investigated comparatively. NGs exhibit smooth surface and multilayer‐stacked structure; most CRGs are in the form of aggregates that are restacked during reduction; while TRGs show a wrinkled topography of relatively thin graphene sheets. The introduction of these graphitic fillers into the PVDF matrix contributes differently to the crystallization, rheological behavior and mechanical properties of the composites. Among them, TRGs show the greatest strengthening effect, as revealed by rheological and dynamic mechanical responses. Compared with chemical reduction technology, thermal reduction is a more economical, environmentally friendly and scalable approach to prepare functionalized graphene sheets. Copyright © 2012 Society of Chemical Industry     

Novel copoly(ether ether ketone)s with pendant phenyl groups: synthesis and characterization

In order to obtain poly(ether ether ketone)s having enhanced solubility and processability without extreme loss of other properties, a series of copoly(ether ether ketone)s (Co‐PEEKs) with pendant phenyl groups were synthesized from 1,1‐bi(4‐hydroxyphenyl)‐1‐phenylethane (ph‐BPA), hydroquinone and 4,4′‐difluorobenzophenone via aromatic nucleophilic substitution reaction. The structures and properties of the Co‐PEEKs were characterized using Fourier transform infrared and ¹H NMR spectroscopies, differential scanning calorimetry, thermogravimetric analysis, wide‐angle X‐ray diffraction and solubility testing. These Co‐PEEKs have inherent viscosities in the range 0.14–1.09 dL g^?1, and their number‐average and weight‐average molecular weights reach 72 659 and 163 400 g mol^?1, respectively. The Co‐PEEK with the lowest content of ph‐BPA has a semi‐crystalline nature and is only soluble in 98% sulfuric acid. However, with an increase of ph‐BPA in the Co‐PEEKs, they become amorphous and readily soluble in a wide range of organic solvents and can afford tough films. These Co‐PEEKs have glass transition temperatures of 137–180 °C depending on the content of ph‐BPA. All the Co‐PEEKs have initial degradation temperatures above 480 °C in nitrogen atmosphere. Thus, these Co‐PEEKs with excellent thermal stability, good solubility and processability have potential for use in high‐performance films, coatings, hollow fiber membranes, etc. Copyright © 2011 Society of Chemical Industry     

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     

Thermal and rheological properties of poly(phenylene sulfide) and poly(ether etherketone) resins and composites

Poly(phenylene sulfide) (PPS) and poly(ether etherketone) (PEEK) are high performance engineering thermoplastics with a unique combination of excellent environmental, mechanical, and thermal properties. Research on the thermal and rheological properties of PPS and PEEK resins and carbon fiber reinforced prepregs are described. Experimental studies of the dynamic viscoelasticity and thermal properties of these materials are summarized. The effects of processing cycles and environment on the thermal and rheological properties are discussed. The effects of the processing environment and the addition of carbon fiber on the thermal stability are reported. Crosslinking of poly(phenylene sulfide) in air, enhancing thermal stability, is also investigated.     

Synthesis and characterization of poly(urethane‐ether)s from calcium salt of p‐hydroxybenzoic acid

The synthesis and characterization of calcium‐containing poly(urethane‐ether)s, having ionic links in the main chain, is reported. Calcium salt of p‐hydroxybenzoic acid (HBA‐Ca) was prepared from p‐hydroxybenzoic acid (HBA) and used as the chain extender in the preparation of calcium‐containing poly(urethane‐ether)s. Poly(urethane‐ether)s, having two different compositions, were prepared by varying the mole ratios of poly(tetramethylene glycol), hexamethylene diisocyanate, and HBA‐Ca. The synthesized poly(urethane‐ether)s were characterized by infrared spectroscopy, thermogravimetric analysis, and dynamic mechanical analysis. The presence of calcium in the polymer chain was confirmed by energy‐dispersive X‐ray analysis. The inherent viscosity of metal‐containing polymers decreased with the increase in the metal content of the polymer. The introduction of metal into the polymer lowers the thermal stability of the polymers as indicated by the decreased initial decomposition temperature. The glass transition temperature (T_g) and the storage modulus of the metal‐containing polymers increase with the increase in metal content presumably due to the formation of physical crosslink's in the polymer. From the mechanical studies of the polymer, it was observed that the metal‐containing polymers exhibit high tensile strength and modulus. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011.     

Branched phenyl‐s‐triazine moieties to enhance thermal properties of phthalonitrile thermosets

Heat‐resistant materials have made tremendous progress in marine, aerospace and microelectronic fields. Herein, a new class of phthalonitrile resins, branched poly(biphenyl ether triphenyl‐s‐triazine) phthalonitriles, were successfully synthesized via a two‐step, one‐pot reaction, on the basis of 2,4,6‐tris(4‐fluorophenyl)‐1,3,5‐triazine and 4,4′‐biphenol. 4,4′‐Diaminodiphenylsulfone was employed to facilitate the curing reaction, and successful realization of curing behavior was concluded from rheological and differential scanning calorimetric studies, indicating the obtained resins possess favorable processability. The relationship between concentration of reactants and properties of the resins was systematically studied. After thermal curing, the E‐glass fiber‐reinforced composite, prepared with a concentration of reactants of 0.15 g mL^?1, shows an admirable glass transition temperature of 480 °C and commendable thermal stability with 5% weight loss temperature in nitrogen of 563 °C, suggesting that the improvement of the thermal properties stems from the branched structure and the phenyl‐s‐triazine units. © 2017 Society of Chemical Industry     

Effect of LCP and rPET as reinforcing materials on rheology,morphology, and thermal properties of in situ microfibrillar‐reinforced elastomer composites

Microfibrillar‐reinforced elastomer composites based on two dispersed phases, liquid crystalline polymer (LCP) and recycled poly(ethylene terephthalate)(rPET), and styrene‐(ethylene butylene)‐styrene (SEBS) were prepared using extrusion process. The rheological behavior, morphology, and thermal stability of SEBS/LCP and SEBS/rPET blends containing various dispersed phase contents were investigated. All blends and LCP exhibited shear thinning behavior, whereas Newtonian fluid behavior was observed for rPET. The incorporation of both LCP and rPET into SEBS significantly improved the processability by bringing down the melt viscosity of the blend system. The fibrillation of LCP dispersed phase was clearly observed in as‐extruded strand with addition of LCP up to 20–30 wt %. Although the viscosity ratio of SEBS/rPET system is very low (0.03), rPET domains mostly appeared as droplets in as‐extruded strand. The results obtained from thermogravimetric analysis suggested that an addition of LCP and rPET into the elastomer matrix improved the thermal resistance significantly in air but not in nitrogen. The simultaneous DSC profiles revealed that the thermal degradation of all polymers examined were endothermic and exothermic in nitrogen and in air, respectively. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Kinetic study of the thermal degradation of poly(aryl ether ketone)s containing 2,7‐naphthalene moieties

The degradation of poly(aryl ether ketone) containing 2,7‐naphthalene moieties was subjected to dynamic and isothermal thermogravimetry in nitrogen and air. The dynamic experiments showed that the initial degradation temperature, temperature for 5% weight loss, and temperature corresponding to the maximum degradation rate of poly(aryl ether ketone) containing 2,7‐naphthalene moieties were a little higher than those of poly(ether ether ketone) and almost independent of the 2,7‐naphthalene moiety content. The thermal stability of poly(aryl ether ketone) containing 2,7‐naphthalene moieties in air was substantially less than that in nitrogen, and the degradation mechanism was more complex. The results obtained under the isothermal conditions were in agreement with the corresponding results obtained in nitrogen and air under the dynamic conditions. In the dynamic experiments, the apparent activation energies for the degradation processes were 240 and 218 kJ/mol in nitrogen and air for the second reaction stage as the heating rate was higher than 5°C/min. In the isothermal experiments, the apparent activation energies for the degradation processes were 222 and 190 kJ/mol in nitrogen and air, respectively. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Thermal degradation of polymers. XVII. Thermal analysis of polyquinazolones and related systems

The thermal characterization of a series of polyquinazolones, poly(quinazolone diones), and polybenzoxazinones by thermal analytical techniques (TG, DSC) is described. Comparative thermal stability measurements by dynamic and isothermal TG in air and N₂ are critically discussed. Kinetic studies by isothermal TG in air and nitrogen leading to activation energies are described. The inherent difficulties in comparative thermal stability studies on complex polymer systems are discussed in terms of their structural and compositional variables and their effect on the assessment parameters used.     

Synthesis and properties of aromatic polyimide,poly(benzoxazole imide), and poly(benzoxazole amide imide)

Two series of heterocyclic aromatic polymers were synthesized from 4,4′‐(4,4′‐isopropylidenediphenoxy)bis(phthaltic anhydride) and 2,2′‐bis(3,4‐dicarboxyphenyl)hexafluoropropane dianhydride by two‐step method. The inherent viscosities were in the range of 24–45 cm³/g. The effects of the rigid benzoxazole group in the backbone of copolymer on the thermal, mechanical, and physical properties were investigated. These polymers exhibit good thermal stability. The temperatures of 5% weight loss (T₅) of these polymers are in the range of 403–530°C in air and 425–539°C in nitrogen. The chard yields of these polymers are in the range of 15–24% in air and 54–61% in nitrogen. These polymers also have high glass‐transition temperatures and a low coefficient of thermal expansion and good mechanical properties. The poly(benzoxazol imide) has a higher tensile strength and modulus than those of neat polyimide. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Blends of high density polyethylene with branched poly(styrene‐co‐dodecyl acrylate): Rheological,mechanical, and thermal properties

Branched poly(styrene‐co‐dodecyl acrylate) (BPSDA) was prepared by the atom transfer radical copolymerization of styrene with dodecyl acrylate using p‐cholomethyl styrene as initiator‐monomer (inimer) and CuCl/Bpy (2,2′‐bipyridine) complex as catalyst. The remarkable discrepancies between the molecular weight determined by gel permeation chmotagraphy and multiangel laser light scattering reveals the highly branched structure of the resulting copolymer. Furthermore, the composition was analyzed by hydrogen nuclear magnetic resonance (¹H NMR), which is consistent with the feed ratio of monomers. Blending of the branched product with high density polyethylene (HDPE) was attempted in haake mixer. The rheological, mechanical, and thermal stability properties of the resulting blends were studied. Compared with pure HDPE, the complex viscosity of blend with addition of 4 wt % BPSDA decreased by 15.9%. While the elongation at break decreased by 5.5% and tensile strength decreased by 4.2%. SEM (scanning electron microscopy) revealed that the average particle size of disperse phase in HDPE/4% BPSDA blend is 0.45 μm in diameter. Differential scanning calorimetry characterization showed that the addition of BPSDA accelerated the relative crystallization rate but decreased the final absolute degree of crystallinity. No obvious change of thermal stability of the blends was observed relative to pure HDPE. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Rheology and extrusion foaming of chain‐branched poly(lactic acid)

In this study, the effect of macromolecular chain‐branching on poly(lactic acid) (PLA) rheology, crystallization, and extrusion foaming was investigated. Two PLA grades, an amorphous and a semi‐crystalline one, were branched using a multifunctional styrene‐acrylic‐epoxy copolymer. The branching of PLA and its foaming were achieved in one‐step extrusion process. Carbon dioxide (CO₂), in concentration up to 9%, was used as expansion agent to obtain foams from the two PLA branched using chain‐extender contents up to 2%. The foams were investigated with respect to their shear and elongational behavior, crystallinity, morphology, and density. The addition of the chain‐extender led to an increase in complex viscosity, elasticity, elongational viscosity, and in the manifestation of the strain‐hardening phenomena. Low‐density foams were obtained at 5–9% CO₂ for semi‐crystalline PLA and only at 9% CO₂ in the case of the amorphous PLA. Differences in foaming behavior were attributed to crystallites formation during the foaming process. The rheological and structural changes associated with PLA chain‐extension lowered the achieved crystallinity but slightly improved the foamability at low CO₂ content. POLYM. ENG. SCI., 2010. © 2009 Society of Plastics Engineers     

Role of 2‐hydroxyethyl end group on the thermal degradation of poly(ethylene terephthalate) and reactive melt mixing of poly(ethylene terephthalate)/poly(ethylene naphthalate) blends

In an attempt to minimize the acetaldehyde formation at the processing temperatures (280–300°C) and the outer–inner transesterification reactions in the poly (ethylene terephthalate) (PET)–poly(ethylene naphthalate) (PEN) melt‐mixed blends, the hydroxyl chain ends of PET were capped using benzoyl chloride. The thermal characterization of the melt‐mixed PET–PEN blends at 300°C, as well as that of the corresponding homopolymers, was performed. Degradations were carried out under dynamic heating and isothermal conditions in both flowing nitrogen and static air atmosphere. The initial decomposition temperatures (T_i) were determined to draw useful information about the overall thermal stability of the studied compounds. Also, the glass transition temperature (T_g) was determined by finding data, indicating that the end‐capped copolymers showed a higher degradation stability compared to the unmodified PET and, when blended with PEN, seemed to be efficient in slowing the kinetic of transesterification leading to, for a finite time, the formation of block copolymers, as determined by ¹H‐NMR analysis. This is strong and direct evidence that the end‐capping of the ? OH chain ends influences the mechanism and the kinetic of transesterification. POLYM. ENG. SCI., 2012. © 2012 Society of Plastics Engineers     

Properties of poly(butylene terephthalate) chain‐extended by epoxycyclohexyl polyhedral oligomeric silsesquioxane

Epoxycyclohexyl polyhedral oligomeric silsesquioxane (epoxy–POSS) was used to prepare a chain‐extended poly(butylene terephthalate) (PBT) with a twin‐screw extruder. The effect of epoxy–POSS on the melt flow index, mechanical properties, rheological behavior, and thermal properties of chain‐extended PBT was investigated. PBT had an intrinsic viscosity of 1.1 dL/g and a carboxy1 content of 21.6 equiv/10⁶ g, but the PBT chain‐extended with 2 wt % epoxy–POSS had an intrinsic viscosity of 1.7 dL/g and a carboxy1 content lower than 7 equiv/10⁶ g. After the addition of epoxy–POSS, the melt flow index of PBT dramatically decreased, the elongation at break increased greatly, the tensile strength increased slightly, and the thermal stability was also improved. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Synthesis of new superhydrophobic nanosilica and investigation of their performance in reinforcement of polysiloxane

We reported a new facile method to synthesize superhydrophobic nanosilica using glycidoxypropyltrimethoxysilane and dodecylamine as treatment agents. Also, we systemically investigate their performance in reinforcement of poly(dimethylsiloxane) (PDMS) rubber. Fourier transform infrared spectrum, contact angle (CA) and thermogravimetric analysis (TGA) measurements were used to characterize the modified nanosilica. Results show that the inherent hydrophilicity of parent nanosilica surface can be greatly altered through this modification method. The CA of as‐prepared superhydrophobic nanosilica can reach 160.2°. The properties of as‐prepared modified nanosilica‐filled PDMS composites were systemically investigated by dynamic rheological test, scanning electron microscopy, TGA, dynamic mechanical analysis. These as‐prepared superhydrophobic nanosilica exhibit uniform dispersion in the PDMS matrix, and their composites also show good mechanical properties and distinct advantage on thermal stability compared with those of the pure silica‐filled PDMS composites. Also described is the probable mechanism for the reinforcement of as‐prepared superhydrophobic nanosilica‐filled PDMS. POLYM. COMPOS., 31:1628–1636, 2010. © 2009 Society of Plastics Engineers     

Rheological behavior of neat and carbon fiber-reinforced poly(ether ketone ketone) for extrusion deposition additive manufacturing

To develop new materials for extrusion additive manufacturing (AM) systems, a fundamental understanding of rheological properties is essential to correlate the effect of processing on material structure and its properties. In this work, the rheological properties of five different grades of neat and carbon fiber (CF)-reinforced poly(ether ketone ketone) are reported. Rheological properties are essential to understand the effect of reinforcing fibers and AM process parameters such as time, temperature, environment, and shear rate on flow behavior during processing. Small-amplitude oscillatory shear tests and steady shear tests indicated neat grades to exhibit less increase in viscosity over time when processed in air than the CF-filled grades. The filled grades showed greater shear thinning and lower sensitivity to temperature. Overall, this rheological analysis provides a broad framework for determining appropriate processing conditions for extrusion deposition AM of such high-temperature polymer systems.     

Synthesis and gas transport properties of novel poly(aryl ether ketone)s with branched structure

Poly(aryl ether ketone)s (PAEKs) based on 2‐(3′‐trifluoromethylphenyl) hydroquinone and 4,4′‐difluorobenzophenone were synthesized and characterized in the presence or absence of 2,4′,6‐trifluorobenzophenone (BB′₂ monomer). The influence of the incorporation of a branched structure (BB′₂ monomer) on the gas transport properties of PAEKs was investigated. The results showed that PAEKs with a branched structure possess a higher permeability and selectivity than PAEKs without a branched structure. Moreover, improvements in the permeability and selectivity were enhanced with increasing content of BB′₂ monomer. This synergistic effect on permeability and selectivity was mainly due to the higher fractional free volume and the unique size and distribution of free volume holes arising from the incorporation of the branched structure. © 2013 Society of Chemical Industry