Rheological study on poly-D(-)(3-hydroxybutyrate) and its blends with poly(ethylene oxide)

Aspects of thermal, morphological, and rheological properties of biodegradable poly-D(-)(3-hydeoxybutyrate) (PHB) blended with poly(ethylene oxide) (PEO) have been studied. Thermal properties and morphology of the blends were examined by scanning electron microscopy and differential scanning calorimetry, respectively. A rotational theometer with parallel plate geometry was also adopted to investigate the rheological properties of these blends. In addition, dynamic ciscoelasticity was measured by a Rheovibron as functions of time and temperature. From these measurements, PHB and PEO were observed to be miscible in the melt state. In the case of the blend systen 80/20 PHB/PEO by weight, the vacant domains of the PHB were filled with PEO particles, and this morphological state enhanced the rheological properties. Furthermore, PHB and its blends were found to have high crystallinities, but to have unstable thermal behavior about T_m.     

Processability modifications of poly(3‐hydroxybutyrate) by plasticizing,blending, and stabilizing

Poly(3‐hydroxybutyrate) (PHB) was plasticized with dioctyl (o‐)phthalate, dioctyl sebacate, and acetyl tributyl citrate (ATBC). The thermal properties, mechanical properties, and melt flow ability were studied with differential scanning calorimetry, thermogravimetric analysis, a universal material testing machine, and a melt flow indexer. ATBC was revealed to be an efficient plasticizer, reducing the glass‐transition temperature and increasing the thermoplasticization ability of PHB. We also blended poly(3‐hydroxybutyrate‐co‐hydroxyhexanoate) (PHBHHx) and poly(3‐hydroxybutyrate‐co‐4‐hydroxybutyrate) [P(3/4HB)] with PHB, ATBC, and antioxidant 1010 to overcome the brittleness of PHB and improve the melt flow stability of the materials. PHBHHx did little to improve the thermal processing but increased the fluidity of PHB, and P(3/4HB) toned the toughness of PHB. The addition of antioxidant 1010 enhanced the thermal stabilization of PHB. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Effect of additives on the melt rheology and thermal degradation of poly[(R)‐3‐hydroxybutyric acid]

Thermal degradation of poly[(R)−3‐hydroxybutyric acid] (PHB) during melt mixing results in random chain scission that produces shorter polymer chains containing crotonic and carboxyl end groups. One way of preventing this serious reduction of molar mass is to add agents that react with at least two of the newly generated end groups. Different types of commercially available additives known to react with carboxyl group, namely bis(3,4‐epoxycyclohexylmethyl) adipate (BECMA), 2,2'‐bis(2‐oxazoline) (BOX), trimethylolpropane tris(2‐methyl‐1‐aziridinepropionate) (PETAP), triphenyl phosphate (TPP), tris(nonylphenyl) phosphate (TNPP), polycarbodiimide (PCDI), and poly(methyl metharylate‐co‐glycidyl methacrylate) (GMA.MMA) were mixed with PHB by cocasting from solution in chloroform. Dynamic rheology as well as measurements of molar masses before and after dynamic analysis was used to evaluate the effect of the additives on the melt stability of PHB. Measurements of the dynamic shear modulus and the molar mass of molten PHB with the additives PCDI and GMA.MMA showed a minor improvement on the thermal stability. Furthermore, TPP and TNPP did not affect the thermal stability of PHB, whereas the presence of BECMA, BOX, and PETAP gave a strong decrease of the dynamic modulus compared with neat PHB. © 2014 The Authors Journal of Applied Polymer Science Published by Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 41836.     

Imaging of nonlinear optical response in biopolyesters via second harmonic generation microscopy and its dependence on the crystalline structures

Nonlinear optical response in various polyhydroxyalkanoates (PHAs) was investigated via second harmonic generation microscopy (SHGM). It was revealed that the second harmonic generation (SHG) efficiency depended on both the polymer chemical structure and the crystalline structure. Among the PHAs studied, the microbial polyesters, poly(R-3-hydroxybutyrate) (PHB) and poly(R-3-hydroxyvalerate) (PHV) showed strongest SHG activity, which could be attributed to hydrogen bonding that enhanced hyperpolarizability of the carbonyl groups in the crystalline lamellar core, and the noncentrosymmetric arrangement of the SHG moieties. The β- and γ-type poly(β-propiolactone) demonstrated different SHG efficiency due to the different packing scheme of the chain stems in the crystal lattice despite the same chain conformation. In addition, SHG response in the banded spherulite varied with the lamellar orientation. Furthermore, SHGM was applied for 3-D imaging of PHB spherulite in PHB/poly(?-caprolactone) blends via optical sectioning of the thick film at different depths. For PHB/poly(l-lactide) (PLLA) blends, SHGM revealed that the PHB twisting lamellae formed from the melt confined between the preformed PLLA twisting lamellae had the same twisting period as the latter, which could not be observed under polarized optical microscope. Due to the advantages, SHGM is expected to find more applications in characterization of nonlinear optical (NLO) materials with heterogeneous structures.     

Unique orientation textures formed in miscible blends of poly(vinylidene fluoride) and poly[(R)-3-hydroxybutyrate]

The oriented crystallization of poly[(R)-3-hydroxybutyrate] (PHB) in the miscible blends with poly(vinylidene fluoride) (PVDF) was investigated with various compositions. The PVDF/PHB blend films were prepared by solution casting and subsequent melt-quenching in ice water. Oriented films of the blends were prepared by uniaxially stretching the melt-quenched film at 0 °C in ice water using a hand-operated stretching apparatus. The oriented blend films were heat-treated at a fixed length in order to crystallize PHB in the oriented state. The crystal orientation and the lamellar textures of the obtained samples were studied with wide-angle X-ray diffraction (WAXD), and small-angle X-ray scattering (SAXS), respectively. The SAXS measurements showed that a considerable amount of molecular chains of PHB are excluded from the lamellar stacks of PVDF and exist in the interfibrillar regions in the oriented films of the blends. The cold crystallization of PHB in the interfibrillar region results in the orientation of PHB crystals, and the type of crystal orientation depends upon the composition of the blends. For the PVDF/PHB=4/6-7/3 blends, the crystal a-axis of PHB is highly oriented parallel to the drawing direction and the crystal c-axis (molecular chain axis) in PHB crystals is perpendicular to the drawing direction, i.e. orthogonal to the chain axis of the crystals of PVDF. It is considered that the a-axis orientation is induced by the confinement of crystal growth in the interfibrillar nano-domains. For the PVDF/PHB=2/8-3/7 blends, however, the crystal c-axis of PHB is primarily oriented in the drawing direction, suggesting that the stressed molecular chains of PHB are crystallized with the molecular orientation retained.     

The Role of Short-Chain Conjugated Poly-(R)-3-Hydroxybutyrate (cPHB) in Protein Folding

Poly-(R)-3-hydroxybutyrate (PHB), a linear polymer of R-3-hydroxybutyrate (R-3HB), is a fundamental constituent of biological cells. Certain prokaryotes accumulate PHB of very high molecular weight (10,000 to >1,000,000 residues), which is segregated within granular deposits in the cytoplasm; however, all prokaryotes and all eukaryotes synthesize PHB of medium-chain length (~100–200 residues) which resides within lipid bilayers or lipid vesicles, and PHB of short-chain length (<12 residues) which is conjugated to proteins (cPHB), primarily proteins in membranes and organelles. The physical properties of cPHB indicate it plays important roles in the targeting and folding of cPHB-proteins. Here we review the occurrence, physical properties and molecular characteristics of cPHB, and discuss its influence on the folding and structure of outer membrane protein A (OmpA) of Escherichia coli.     

Rheology of poly(propylene)/clay nanocomposites

The linear and nonlinear shear rheological behaviors of poly(propylene) (PP)/clay (organophilic‐montmorillonite) nanocomposites (PP/org‐MMT) were investigated by an ARES rheometer. The materials were prepared by melt intercalation with maleic anhydride functionalized PP as a compatibilizer. The storage moduli (G′), loss moduli (G″), and dynamic viscosities of polymer/clay nanocomposites (PPCNs) increase monotonically with org‐MMT content. The presence of org‐MMT leads to pseudo‐solid‐like behaviors and slower relaxation behaviors of PPCN melts. For all samples, the dependence of G′ and G″ on ω shows nonterminal behaviors. At lower frequency, the steady shear viscosities of PPCNs increase with org‐MMT content. However, the PPCN melts show a greater shear thinning tendency than pure PP melt because of the preferential orientation of the MMT layers. Therefore, PPCNs have higher moduli but better processibility compared with pure PP.© 2003 Wiley Periodicals, Inc. J Appl Polym Sci 91: 2427–2434,2004     

Peroxide induced cross‐linking by reactive melt processing of two biopolyesters: Poly(3‐hydroxybutyrate) and poly(l‐lactic acid) to improve their melting processability

Poly(3‐hydroxybutyrate) (PHB) and poly(l ‐lactic acid) (PLLA) were individually cross‐linked with dicumyl peroxide (DCP) (0.25–1 wt %) by reactive melt processing. The cross‐linked structures of the polymer gel were investigated by nuclear magnetic resonance (NMR) and Fourier transform infrared (FTIR) spectroscopies. The size of the polymer crystal spherulites, glass transition temperature (T_g), melting transition temperature (T_m), and crystallinity were all decreased as a result of cross‐linking. Cross‐linking density (ν_e) was shown to increase with DCP concentration. Based on parallel plate rheological study (dynamic and steady shear), elastic and viscous modulus (G″ and G′), complex viscosity (η^*) and steady shear viscosity (η) were all shown to increase with cross‐linking. Cross‐linked PHB and PLLA showed broader molar mass distribution and formation of long chain branching (LCB) as estimated by RheoMWD. Improvements in melt strength offer bioplastic processors improved material properties and processing options, such as foaming and thermoforming, for new applications. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 41724.     

Effect of monomer composition on the rheological properties of poly(p-oxybenzoate-co-ethylene terephthalate)s

Summary Effect of monomer composition on the dynamic viscoelastic properties and the steady flow properties of thermotropic liquid crystalline poly (p-oxybenzoate-co-ethylene terephthalate)s in the fluid state have been investigated as compared with the isotropic melt of the copolyester including 28 mol% p-oxybenzoate unit (POB). The liquid crystalline copolyesters show the rheological transition temperature, which increases with increasing the content of POB unit. Above the transition temperature, all the thermotropic copolyesters exhibit much higher compliance and much more shear-thinning behavior of the apparent viscosity than the isotropic melt of the non-liquid crystalline copolyester.     

二异氰酸酯对聚碳酸亚丙酯熔体流变性能的影响

以4,4-二苯基甲烷二异氰酸酯（MDI）为扩链剂,在转矩流变仪上通过一步法对聚碳酸亚丙酯（PPC）进行了熔融扩链改性。结果表明,随着MDI用量的增加,扩链反应峰和平衡扭矩逐渐增大、平衡时间不断延长;红外光谱分析表明,扩链改性后的PPC在1600 、1535 cm-1处分别出现了苯环的骨架振动吸收峰和-NH的特征吸收峰;旋转流变分析表明,扩链改性后PPC的储能模量、损耗模量和复数黏度均随MDI用量的增加而增加;从Cole-Cole曲线可以看出,随着MDI用量的增加,扩链改性后PPC的相对分子质量逐渐增加,相对分子质量分布变宽,支化度提高;应力松弛测试结果表明,随着MDI用量的增加,松弛时间逐渐增加。     

Functionalization of MWCNT with P(MMA-co-S) copolymers via ATRP: Influence on localization of MWCNT in SAN/PPE 40/60 blends and on rheological and dielectric properties of the composites

In this work, the localization of functionalized multi-walled carbon nanotubes (MWCNT) with random copolymers of methyl methacrylate and styrene (P(MMA-co-S)) in poly(styrene-co-acrylonitrile)/poly(2, 6-dimethyl-1,4-phenylene ether) blends (SAN/PPE) and its influence on morphological, rheological and dielectric properties of the composites were investigated. P(MMA-co-S) copolymers were grafted onto MWCNT via atom transfer radical polymerization (ATRP). The molecular weight of the copolymers was adjusted by controlling the time of reaction. In SAN/PPE blends, MWCNT grafted with low molecular weight copolymers were predominantly located at the interface of the blend and a few individual tubes were dispersed in the PPE phase. Aggregation of MWCNT was observed nearby the interfacial region because of micellization of grafted copolymers. Aggregation was more pronounced with increasing molecular weight of the grafted P(MMA-co-S) copolymer. In the melt, the composite containing MWCNT with low molecular weight copolymers had higher dynamic moduli than the one with pristine MWCNT. An increasing molecular weight of grafted copolymer led to a softening effect which resulted in a reduction of the moduli of the composite. Although a pronounced enhancement was observed for the composites with pristine MWCNT, only a small increase in electrical conductivity was achieved by adding functionalized MWCNT owing to the poor network formed by functionalized MWCNT in the blends.     

Rheological and thermal behaviors of commercial poly(aryletherketone)s

The mechanical properties and thermal stability of several grades of poly(aryletherketone)s (PAEKs) were investigated using thermal, rheological, and dynamic mechanical characterization. Detailed rheological characterization revealed that several grades of poly(etheretherketone) (PEEK) exhibit relaxation behavior characteristic of a long‐chain branched structure. The potentially branched PEEKs showed greater mechanical damping behavior than the linear‐chain PEEKs. The molecular weight dependence on zero‐shear viscosity for several linear‐chain polymers indicates that the PEEKs behave as rigid chains in the melt. Differences in chain structure do not significantly influence dynamic mechanical behavior in the solid state but affect stability at elevated temperatures. The potentially branched PEEKs are most susceptible to oxidation in air, but exhibit much greater stability in nitrogen. Poly(etherketone) is highly susceptible to degradation in both air and nitrogen environments. Implications of this study for development of high‐performance PAEKs are discussed. POLYM. ENG. SCI. 2013. © 2012 Society of Plastics Engineers     

Thermal, morphological and rheological characterization of poly(acrylic acid-g-styrene) amphiphilic graft copolymers

A family of amphiphilic poly(acrylic acid-g-styrene), P(AA-g-S), graft copolymers has been prepared by quantitative hydrolysis from poly(tert-butyl acrylate-g-styrene), P(tBA-g-S), precursors and evaluated by ¹H NMR and FTIR. The thermal characterization of these copolymers as a function of the number of grafted repeat units has been performed by thermogravimetric analysis, TGA, differential scanning calorimetry, DSC, and dynamic mechanical experiments. A higher thermal stability of the PAA main chain was observed by TGA as incompatible PS is grafted onto it. Small-angle X-ray scattering, SAXS, measurements have confirmed the existence of phase separation in the graft copolymers and the morphological behavior was analyzed. An increase on microdomains size is observed when the number of grafts diminishes. Moreover, the presence of polar functional groups in the backbone chain leads to the formation of hydrogen bonds giving rise to a substantial modification of the linear viscoelastic response compared with that exhibited by the unhydrolyzed precursory copolymers, as observed by analysis of melt rheological measurements.     

Small-angle X-ray scattering and linear melt rheologyof poly(tert-butyl acrylate-g-styrene) graft copolymers

The morphology and rheological properties have been studied for poly(tert-butyl acrylate-g-styrene), PtBA-g-S, graft copolymers through the analysis of different samples that varied in the number of grafted repeat units. Small-angle X-ray scattering (SAXS) measurements confirmed phase separation in these samples, and showed the presence of disordered microdomains on those copolymers with a grafting number higher than 7. SAXS results have also shown a significant improvement of microdomain segregation with temperature manifesting considerable changes in both intensity, position and full-width half-maximum of the peak q*, which is attributed to the graft-like nature of these systems. The frequency dependence of the dynamic moduli revealed three relaxation mechanisms. The low-frequency (long time) relaxation was identified with the movement of the whole molecule, the relaxation at intermediate time is related to movement of the grafts, and the high-frequency relaxation is like that found in the transition zone of main chain of poly(tert-butyl acrylate), PtBA. The rheological measurements indicated that the introduction of a small amount of polystyrene, PS, grafts in the PtBA backbone is sufficient to modify mechanical behaviour at low frequencies. Comparison of the rheological properties of the graft copolymers with higher PS content showed that the observed changes in the viscoelastic behaviour under shear seems to be related to both the microphase separated microstructure and the number of grafts present in the copolymers.     

Analysis of the drying process of a biopolymer (poly-hydroxybutyrate) in rotating-pulsed fluidized bed

A rotating-pulsed fluidized bed (RPFB) dryer was employed to conduct the drying of poly-hydroxybutyrate (PHB) cohesive granules. Along the experiments, it was possible to identify, visually, 3 different dynamic regimes that were related with the temperature profile, the drying kinetics and the fluid dynamic behavior. The drying kinetics of PHB showed a short constant drying rate period followed by a decreasing drying rate period. The constant drying rate (N_c) and final moisture content (dry basis) were related to the rotation frequency (responsible for the pulsation effect), temperature and velocity of the inlet air. Furthermore, measurements of molecular mass (gel permeation chromatography analysis) and Carr Index (flowability test) on PHB samples were done before and after the drying. The RPFB dryer showed to be appropriate to dry the PHB granules, resulting in an excellent fluid dynamic behavior that provided uniform drying of the solid. The best conditions of drying were identified at 7 Hz of rotation frequency, 90 °C and 0.55 m/s of inlet air temperature and velocity. At these conditions the dried PHB reached final moisture content of 0.56% (wet basis) after 2 h of drying.     

Structure‐rheology responses of polylactide/calcium carbonate composites

Polylactide (PLA) and calcium carbonate (CaCO₃) were melt blended using a twin‐screw extruder. The morphology of PLA/CaCO₃ composites was observed by scanning electronic microscopy. The linear and nonlinear shear rheological behaviors of PLA/CaCO₃ melts were investigated by an advanced rheology expended system. The results show that the CaCO₃ particles are evenly dispersed in the PLA matrix. The incorporation of low CaCO₃ content (<20%) causes the reduction of the storage moduli, loss moduli, and dynamic viscosities whereas high CaCO₃ content (>30%) leads to the increase of the storage moduli, loss moduli, and dynamic viscosities. The composites with high CaCO₃ content show pseudo‐solid‐like behaviors at low frequency. High CaCO₃ content also results in a significant increase of flow activation energy and a dramatic decrease of flow index n, which is in consistent with the more serious shear‐thinning tendency of high‐filled PLA composites melts. The particular rheological responses might be attributed to the formation and destruction of the percolating network. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Melt spinning and annealing of poly(ethylene terephthalate)/p‐hydroxybenzoate liquid crystalline polymer

Poly(ethylene terephthalate)/p‐hydroxybenzoate (PET/PHB) copolymer materials have relatively low melt viscosity because of the 60 mol % PHB material having a value that is lower by approximately two orders of magnitude than the value for PET homopolymer. The structure development during melt spinning and thermal treatment (annealing) of liquid crystalline copolyesters, with a rigid backbone structure, were analyzed through the density, birefringence, X‐ray diffraction, DSC, dynamic viscoelasticity, and tensile testing. As the take‐up velocity increased, the birefringence of PET/PHB as‐spun fiber increased, which indicated that it directly influenced the initial modulus and specific stress. The lateral packing of PHB molecular chain in a copolymer was shown to be loosened in the course of thermal treatment. The thermal treatment slightly increased the crystal orientation factor, whereas total molecular orientation was decreased by annealing. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 94: 1265–1278, 2004     

Thermal and rheological properties of modified polyhydroxybutyrate (PHB)

With the discussion of sustainability and the increased environmental awareness, the biopolymer poly‐β‐hydroxybutyrate (PHB) has gained more and more attention in recent years. It derives from renewable sources and can degrade in different environments to carbon dioxide and water. A hindrance for its potential application in plastics parts is its brittleness, deficiency in thermal stability and low crystallization rate. To overcome these problems chemical modification of PHB by reactive extrusion was carried out in a solvent‐free one‐step process by means of a twin screw extruder. Thermal and rheological characterization confirmed the branching and partial crosslinking of PHB by the organic peroxide tert.‐butylperoxybenzoate as well as by the reaction assisted multi‐functional coagents triallyl cyanurate and divinylbenzene. The crystallization temperature of the modified PHB could be significantly increased, up to 16 K, accompanied with an enhanced crystallization rate. Rheological studies show a distinct increase in the melt viscosity and the elastic properties dependent on the modifier content. The addition of plasticizers like rapeseed oil or polyethylene glycols (PEG 1500 and PEG 4000), respectively, lead to an increase in melt extensibility and melt viscosity. In case of PHB modified with PEG 1500, degradation reactions could be substantially retarded. POLYM. ENG. SCI., 59:1057–1064, 2019. © 2019 Society of Plastics Engineers     

The Smectic Rheology of a Polysiloxane Side Chain Liquid Crystalline Polymer

The rheology of a side chain liquid crystalline polymer (SLCP) with a polysiloxane backbone was investigated. The dynamic shear moduli of the SLCP in a smectic phase did not show the normal terminal behavior as the homogenous polymeric melts did, and instead, they tended to level off in the low frequency terminal zone. Time–temperature superposition failed for both dynamic moduli in the low frequency terminal zone and the departure from the superposition became more evident in the vicinity of smectic/isotropic transition. The plateau-like moduli in the terminal zone indicated the layer structure of the smectic phase. The steady shear viscosities of the smectic phase exhibited a shear thinning behavior over the shear rates investigated. The shear thinning was lost at low shear rates when the temperature passed the smectic/biphasic border. The shear viscosity and the dynamic moduli showed a divergence in the neighborhood of the smectic/isotropic temperature. The activation energies of the shear viscosity and the moduli were smaller than that of the SLCP with polymethacrylate backbone. The rheological behavior of the SLCP at low frequencies and low shear rates was dominated by the smectogen.     

Dynamic mechanical and rheological properties of metallocene-catalyzed long-chain-branched ethylene/propylene copolymers

The dynamic mechanical and rheological properties of five long-chain branched (LCB) and three linear ethylene/propylene (EP) copolymers were investigated and compared using a dynamic mechanical analyzer (DMA) and an oscillatory rheometer. The novel series of LCB EP copolymers were synthesized with a constrained geometry catalyst (CGC), [C₅Me₄(SiMe₂N^tBu)]TiMe₂, and had various propylene molar fractions of 0.01-0.11 and long-chain branch frequencies (LCBF) of 0.05-0.22. The linear EP copolymers were synthesized with an ansa-zirconocene catalyst, rac-Et(Ind)₂ZrCl₂ (EBI), and contained similar levels of propylene incorporation as the CGC copolymers, but no LCB. In dynamic mechanical analysis, the dynamic storage moduli (G′) and loss moduli (G″) of the copolymers decreased with an increase of propylene molar fraction. The α- and β-transitions of the CGC copolymers were overlaid with each other. High damping (tan δ) values were found with the CGC copolymers at temperatures below 0 °C. In oscillatory rheological analysis, compared to the linear EBI counterparts, the LCB CGC copolymer melts showed higher zero shear activation energies, broader plateaus of δ and larger elastic contributions, which are essential characteristics of LCB polymers. It was found that the long chain branching was the determining factor in controlling rheological properties of the polymer melts while the short chain branching from propylene incorporation played a decisive role in affecting dynamic mechanical properties. This work represents the first rheological evidence of LCB in EP copolymers synthesized with CGC.