Mobility Of Molecular Chains Research Articles

Effect of electron beam irradiation on the crystallization of silk fibroin fiber‐reinforced poly(ε‐caprolactone) biocomposites

AbstractIn the medical industry, ionizing radiation has attracted increasing interest in recent years for the sterilization of biomedical materials due to its high effectiveness at relatively low cost and simple operation. In the study reported here, silk fibroin (SF) fiber was used to prepare novel reinforced poly(ε‐caprolactone) (PCL) biocomposites, and the effect of electron beam irradiation on both non‐isothermal and isothermal crystallization kinetics of the SF/PCL biocomposites was investigated. The models of Ozawa treatment, Avrami analysis and regime theory of crystal growth are applicable for describing the non‐isothermal and isothermal crystallization kinetics of the irradiated PCL and SF/PCL composites. Compared with non‐irradiated PCL and SF/PCL composites, the irradiated specimens exhibit the same crystallization regime (regime II) and similar lateral surface free energy (σ), except for smaller fold surface free energy (σe) and work of chain folding (q). The crosslinked PCL network formed in the irradiation process can act as a nucleation agent and accelerate the primary crystallization of PCL. However, the restriction effect of the crosslinked PCL network on the molecular chain mobility will reduce the overall crystallization rate of PCL, and this restriction effect appears stronger in the non‐isothermal crystallization process than in the isothermal crystallization process. Copyright © 2009 Society of Chemical Industry

Study on a novel ion‐conductive compound plasticizer for soft and antistatic PVC materials

AbstractIon‐conductive plasticizers (ICP) composed of dibutyl phthalate (DBP) and butyl 2‐poly(ethylene glycol) phthalate (BPEGP)/lithium bisoxalato borate (LiBOB) were successfully synthesized. The composites blended of poly(vinyl chloride) (PVC) and ICP were fabricated in a Haake torque rheometer. FTIR, surface resistivity measurement, and mechanical test were used to investigate the comprehensive properties of the PVC/ICP composites. The results show that all the synthesized ICP can reduce the surface resistivity of the PVC/ICP composites to 105 Ω sq−1 orders of magnitude as the content of ICP reaches 50 phr. The increasing temperature enhances both the mobility of PEG molecular chains and the diffusion of lithium cations, and thus effectively improves the antistatic ability of the PVC/ICP compounds. With two exceptions of PVC/ICP compounds which include those made of PEG800 and PEG1000, the temperature dependence of the surface resistivity of PVC/ICP does not obey the Arrhenius relationship. The introduction of ICP into PVC matrix would improve the antistatic ability of the composites remarkably. Meanwhile, the mechanical properties of the composites are reduced to some reasonable extent. POLYM. ENG. SCI., 2010. © 2009 Society of Plastics Engineers

Morphology, rheological behavior, and thermal stability of PLA/PBSA/POSS composites

AbstractOctavinyl POSS (vPOSS) and epoxycyclohexyl POSS (ePOSS) were separately incorporated into the poly(lactic acid)/poly(butylene succinate‐co‐adipate) (PLA/PBSA) blend by melt mixing. Field emission scanning electron microscopy and X‐ray diffraction analysis revealed that vPOSS existed as crystalline aggregates, whereas ePOSS was more uniformly dispersed in the composites. The storage modulus and complex viscosity slightly decreased after the addition of vPOSS, but significantly increased after the addition of ePOSS, indicating the higher melt elasicity and broader processing window of the PLA/PBSA after the addition of ePOSS. The chloroform solutions of PLA/PBSA/ePOSS composites were turbid in appearance, and the extracted POSS showed absorbant peaks assigned to the vibration of OH and CO groups in the Fourier transform infrared spectroscopy analysis, indicating the reactions between ePOSS and the PLA/PBSA. Polarized optical microscopy analysis revealed that the two types of POSS could act as nucleating agents for PLA, and enhance its crystallization ability. Thermal gravimetric analysis showed that the addition of the two types of POSS increased the decomposition temperature and activation energy, consequently retarding the thermal degradation of PLA/PBSA. The retardation of degradation is more significant with the addition of ePOSS, for the reactions reduced the end groups of PLA/PBSA as well as the molecular chain mobility. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci 2009

Isothermal crystallization kinetics of silk fibroin fiber‐reinforced poly(ε‐caprolactone) biocomposites

AbstractBACKGROUND: Poly(ε‐caprolactone) (PCL) has attracted great attention due to its wide applications for pharmaceutical controlled released systems and implanted polymer devices. In this study, silk fibroin fiber (SF) obtained from degumming treatment of silk was used to prepare novel reinforced PCL biocomposites. The isothermal crystallization behavior of these composites was investigated using differential scanning calorimetry measurements.RESULTS: With a decrease of isothermal crystallization temperature (Tc) and an increase of fiber filler, the crystallization time of the SF/PCL composites becomes shorter, the crystallization rate constant (K) increases and the Avrami exponent (n) gradually decreases (being between 1 and 2). The crystallization of PCL and SF/PCL composites occurs in the same regime. With the gradual addition of fiber, lateral surface free energy (σ) is nearly unchanged, but fold surface free energy (σe) decreases.CONCLUSION: Heterogeneous nucleation is dominant and different growth morphologies coexist during the isothermal crystallization process of the SF/PCL hybrid systems. Although the introduction of SF obviously increases the overall crystallization rate of PCL, the growth rate constant and nucleation constant of PCL are reduced because of the confinement effect of fiber network structures on the molecular mobility of polymer molecular chains. Copyright © 2009 Society of Chemical Industry

Role of boric acid in the formation of poly(vinyl alcohol)–iodine complexes in undrawn films

The role of boric acid in the formation of poly(vinyl alcohol) (PVA)–iodine complexes in undrawn films has been investigated by using wide-angle X-ray diffraction (WAXD) and high-resolution solid-state 13C NMR spectroscopy. From UV–vis absorption spectroscopy, it is confirmed that boric acid is necessary for the formation of the complexes in films that are treated with I 2/KI aqueous solutions at relatively low I 2 concentrations. The WAXD profiles indicate that, irrespective of the presence of iodine, crystallite sizes perpendicular to the chain axis become smaller by the addition of boric acid in the swelling media. Moreover, small crystallites and surficial parts of larger crystallites may be partially dissolved in the swelling process with water and boric acid suppresses the re-crystallization in the drying process with or without iodine. The 13C spin–lattice relaxation time analysis reveals that there exist two components called the mobile and the less mobile components in the films and the latter component, which contains the complexes and the crystalline component, is increased in the fraction by the presence of boric acid. The evaluation of the CH resonance line shows that some of the intermolecular hydrogen bonds are broken by boric acid, which increases the intramolecular hydrogen bonds. The CH 2 lineshape analysis also reveals that the gauche fraction is appreciably increased in the less mobile component by the addition of boric acid. These facts suggest that boric acid may promote the formation of PVA–iodine complexes particularly in the surficial areas of the crystallites probably by reducing the molecular mobility of the PVA chains by causing cross-linking among them.

ものづくりを支える分析技術 耐衝撃性ポリマーアロイ

We have already represented that high impact mechanism of polyketone/polyamide alloy (PK/PA) is enhanced by the moisture absorption. It was thought the high impact mechanism depends on ductility caused by the moisture absorption of the alloy. This time we have investigated the nano-meter level phase separation structure of PK/PA alloys by using a TEM, an EELS and a 3D-TEM observation. It is found that the PK rich phase and the PA rich one form their co-continuous structure. Surprisingly, the three-dimensional lamella network structure is extended in the PK rich phase. Next, we have carried out SAXS measurements to evaluate lamella network structure. Moreover, the interaction and the mobility of PK and PA molecular chain of the wet and dry polymer alloy have been investigated by using solid-state high resolution NMR techniques. It was found that the moisture absorption enhances the molecular mobility of PA, and flexibility is given to the polymer alloy. The above-mentioned results revealed that the co-continuous structure and the higher-order structure are closely related to the impact properties.

The thickness dependence of elastic modulus of organosilane interphases

AbstractSeries of organosilanes with varying molecular structure was deposited onto E glass. Solution coating and rf plasma enhanced Chemical Vapor Deposition (PE‐CVD) techniques were used. Thickness of the deposited layers varied from 30 nm to 106 nm. Vibrational piezoelectric resonator technique and the speed of Rayleigh wave measurement were used to determine elastic modulus of the layers deposited on the glass substrate as a function of layer thickness. In all cases, increase of the Young modulus, E, of the organosilane layer with decreasing layer thickness was observed. Solution deposited layers exhibited always significantly lower elastic moduli compared to the layers deposited using PE‐CVD technique. Elastic moduli of deposited layers increased with increasing hydrocarbon chain rigidity at comparable chain length. Chlorosilane interlayers possessed always significantly greater elastic modulus compared to their ethoxy‐analogues. The observed increase of E with the decreasing layer thickness was ascribed to the reduction of the molecular mobility of chains near solid surface compared to their mobility in the bulk. It was shown that increasing the bond strength between the deposited layer and the solid E‐glass substrate resulted in immobilized region with constraints imposed by the surface spanning into a distance from the surface. This was in agreement with current models of reinforcement mechanism in nanocomposites based on the idea of immobilized entanglements. It was shown that the deposition technique plays important role in controlling the structure and properties of the deposited interphase. POLYM. COMPOS., 2008. © 2008 Society of Plastics Engineers

Influence of molecular weight on the electrification of linear polyethylenes during extrusion: Identification of two different mechanisms for charge generation

AbstractThe phenomenon of electrification is the accumulation of electric charge in a material. Polymers may become electrified when subjected to intense friction during their processing or under working conditions and the accumulated electric charge may change their adhesion and friction properties. In this work, a study of the influence of molecular weight and chain mobility on the electrification of linear low‐density polyethylenes under continuous extrusion is presented. The use of different die materials, polymer processing additives, as well as slip and no slip flow conditions allowed the identification of two different mechanisms for electric charge generation in the melts; namely, the stripping of an electrical double layer acting in the absence of slip, and dynamic frictional electrification, or tribocharging acting under strong slip conditions. The magnitude of the electric charge was found to increase with polymer molecular weight and die length, and exhibited a local maximum as a function of the average velocity of the melt in both cases. The height of the maximum increased along with the molecular mobility. The experimental results were compared with the numerical solution of the equation of continuity for charge transport and it is shown that it does not describe the experimental results because it does not consider the additional mechanism of charge generation introduced by strong slip at the die wall. POLYM. ENG. SCI., 2008. © 2007 Society of Plastics Engineers

Thickness dependence of elastic modulus of polycarbonate interphase

The oligomer of bis-phenol A (oligo-PC) with M w = 1300 and bis-phenol A polycar-bonate (PC) with M w = 20 000 were deposited onto E-glass surface using SiCl4 as the grafting and cross-linking agent. Thickness of the deposited layers was varied from 30 to 106 nm and the layers were investigated as prepared and after thermal annealing at 245°C for 10 min in the air. Vibrational piezoelectric resonator technique and the speed of Rayleigh wave measurement were used to determine elastic moduli of the ultra thin layers deposited on flat E-glass substrate as a function of their thickness. In all cases, increase of the Young modulus of the interphase, E i, with decreasing layer thickness, t i, was observed. At a given thickness, the E i of PC layer was significantly lower than that for the oligo-PC layer. Thermal annealing of the deposited PC layer resulted in a significant increase of its E i compared to the as received layer. No significant change was observed for oligo-PC interphases. Increase of the shear strength of the interface, τ a, with reducing interphase thickness, t i, was observed. The observed increase of E i with the decreasing t i was ascribed to the reduction of the molecular mobility of chains near solid surface compared to their mobility in the bulk. Most probably, the observed increase of E i after thermal annealing of PC was caused by rearrangement of both segment density distribution in individual PC coils near the solid surface and cooperative rearrangements of multiple PC chains. Since the oligomers attached to the surface attained presumably more regular extended conformations with lower conformation entropy compared to the PC random coils, the effect of thermal annealing was negligible. In agreement with theoretical predictions, increase of E i at the same extent of interfacial interactions resulted in the observed increase of the τ a measured using the single embedded fiber test.

Study on the viscoelastic properties of the epoxy surface by means of nanodynamic mechanical analysis

AbstractThe viscoelastic properties of the epoxy surface have been investigated by nanodynamic mechanical analysis (nano‐DMA). Both a Berkovich tip and a conospherical tip were used under the condition of different forces (i.e., different penetration depths) in the frequency range of 10–200 Hz. Loss tangent and storage modulus are characteristics that describe the viscoelastic properties. The effect of force frequency, penetration depth, and tip shape on the viscoelastic properties is studied and discussed according to the features of microstructures and mobility of molecular chains. The experimental results show important variations when the penetration depth is shallow (<30 nm). As the depth becomes deeper, the results tend to be stable and become almost constant over 120 nm. The two kinds of indenter tip can cause a slight difference of the storage modulus. A “master curve” of the storage modulus as a function of force frequency is established. © 2007 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 46: 281–288, 2008

Filled Elastomers: Characteristics and Properties of Interfaces and Interphases, and Their Role in Reinforcement Processes

The dispersion of fillers in polymers is generally associated with an improvement of at least some of the properties (mechanical, thermal, electrical, etc.) of the corresponding macromolecular material. These phenomena are known to result from the interactions, which take place at the molecular level between the polymer and the surface of the filler and result in the formation of a so‐called interphase. It is, thus, of the utmost importance to be in a position to assess the characteristics of the latter. In this article, we will report on the particular case of elastomers interacting with reinforcing fillers—such as carbon black or silica—the information which may be provided by approaching the segmental mobility of a polymer in close proximity to a solid surface. In this respect, we will discuss the effect of compounding conditions on the adsorption of rubber chains (amount of adsorbed polymer, possible chain conformations, intensity of adsorption, filler/polymer networking) and examine the thermodynamic state of the corresponding elastomer by assessing the molecular mobility of the macromolecular chains through solid‐state NMR spectrometry, physical aging processes, and so on.

Synthesis of nano-sized TiO 2/poly(AA- co-MMA) composites by heterocoagulation and blending with PET

Nano-sized TiO 2 or SiO 2/TiO 2 particles were prepared by hydrolysis and condensation reactions in aqueous media, followed by mixing with poly(AA- co-MMA) latex to form different composites, then blending with poly(ethylene terephthalate), PET. The TGA results of composites indicated that negative charged latexes had greater interaction with TiO 2/ or SiO 2/TiO 2 particles through strong electrostatic forces, while cationic latexes incorporated with TiO 2 or SiO 2/TiO 2 particles by pH induced coagulation, carbonyl group chelation and hydrogen bonding. The soapless latex polymer particles showed lower ability of adsorption to TiO 2 particles due to the decrease of total surface area of these larger particles. If SiO 2/TiO 2 particles were used instead of TiO 2 particles, unexpected high adsorption result was observed. Morphology results observed by SEM showed that PET blended with positive charged composites was more homogeneous than PET blended with negative charged composites. DSC results also indicated that the T g of PET was increased, melting temperatures ( T m or T m ′ ) were increased, and the temperature range of crystallization was narrowed after blending with the composites. The presence of composites affected the mobility and packing of PET molecular chains therefore changing the thermal properties of PET.

Effect of structure and conformational composition on the transport behavior of poly(ether imides)

With the example of two isostructural poly(ether imides), the effects of isopropylidene and hexafluoroisopropylidene groups and hydrogen bonding with chloroform on changes in geometry and energy parameters of polymer chains have been analyzed. The relationship between changes in the geometry characteristics of polymer chains and the gas-separation behavior of films cast from these poly(ether imides) has been established. It has been shown that an increase in permeability is related to a rise in rotation barriers and, consequently, to enhancement of chain rigidity, while the improvement of gas-separation selectivity is associated with a reduction in the amount of isoenergy conformers and an increase in the conformational uniformity of polymer chains. As was detected by FTIR spectroscopy and confirmed by quantum-chemical calculations, the conformational nonuniformity and the small-scale mobility of poly(ether imide) chains are possible only in the Ph-O-Ph′ fragment. The data obtained are applicable for estimation of the role of molecular mobility of polymer chains in the mechanism of gas or penetrant transfer through the polymer film and for predicting the transport behavior of polymers from this family. With the example of two other poly(ether imides), the prediction is confirmed by the experimental data on gas separation.

Cotton Fibers Encapsulated with Homo- and Block Copolymers: Synthesis by the Atom Transfer Radical Polymerization Grafting-From Technique and Solid-State NMR Dynamic Investigations

Cotton fibers were modified by surface-initiated atom transfer radical polymerization of ethyl acrylate (EA) followed by copolymerization with styrene. Either ethyl 2-bromopropionate as a sacrificial free initiator or Cu(II) as a deactivator was used to optimize the EA grafting yield and to preserve the livingness of the chain ends for the subsequent growth of a poly(styrene) (PSty) block from the poly(ethyl acrylate) (PEA) grafts. The polymer-encapsulated cotton fibers were analyzed by Fourier transform infrared spectroscopy, scanning electron microscopy, differential scanning calorimetry (DSC), thermogravimetric analysis, and solid-state NMR (high-resolution 13C cross-polarization magic angle spinning, 1H spin-lattice relaxation times, and 1H free induction decay analysis NMR). The latter allowed the detection of the dynamic modifications associated with the presence of homo- and block copolymer grafts. In particular, the results of the DSC and NMR investigations suggest a heterogeneous morphology of the g-PEA-b-PSty grafted skin, which could be described as an inner layer of g-PEA sandwiched between the semicrystalline cellulose of the core fiber and the high glass transition temperature PSty of the covalently linked outer layer. Such morphology results in a reduced molecular mobility of the PEA chains.

Surface and interface viscoelastic behaviors of thin polymer films investigated by nanoindentation

Nanoindentation experiments were performed on poly(methyl methacrylate) films deposited on Si(100) substrates to investigate the effects of film thickness, loading rate, and molecular weight on the surface and interface viscoelastic behaviors. The film stiffness increased with the indentation depth due to the increase of the contact area and the effect of the rigid substrate. The film thickness and loading rate exhibited strong effects on the film stiffness, while the molecular weight effect was secondary. For film thickness greater than the unperturbed radius of gyration, the stiffness variation across the film thickness demonstrated the existence of three regimes of different viscoelastic behaviors. The loading rate effect on the viscoelastic behavior of the indented polymer films is interpreted in terms of the confinement between the indenter and the substrate surfaces that restricted the molecular chain mobility in the vicinity of the film/substrate interface. The through-thickness variation of the film stiffness (modified to exclude the viscous component) is examined in the context of a previous indentation model. The nanoscale viscoelastic behavior of the thin polymer films observed in this study has important implications in polymer nanostructuring and nanopatterning.

Viscoelastic properties of polymer surfaces investigated by nanoscale dynamic mechanical analysis

The viscoelastic properties of polymer surfaces were investigated by nanoscale dynamic mechanical analysis (nano-DMA) involving contact force modulation in the frequency range of 10–200Hz. Nano-DMA experiments were performed with a Berkovich diamond tip of nominal radius of curvature equal to ∼100nm under a mean contact force of 8–10μN and alternating force equal to 2% of the mean force. Variations in the loss tangent, storage modulus, and loss modulus of low- and high-density polyethylene and ultrahigh molecular weight polyethylene with the force frequency demonstrated significantly different viscoelastic behaviors for shallow depths (<40nm) than for relatively large depths (i.e., 75–100nm). The effects of alternating force frequency and indentation depth on the viscoelastic properties of the different polyethylene materials are interpreted in terms of the microstructure characteristics and the molecular chain mobility at the polymer surfaces. The results show that nano-DMA is an effective technique for nanoscale studies of the viscoelastic behavior of polymer surfaces.

The kinetics of thermal degradation and the structure of bisphenol-A epoxy binder modified by active plasticizer

The kinetics of thermal degradation and the molecular mobility of a bisphenol-A epoxy binder obtained by curing the oligomer ED-20 in the presence of various amounts of epoxidized diethylene glycol as an active plasticizer were studied. It was shown that polyepoxies modified with this plasticizer formed a one-phase system; as the plasticizer mass fraction is increased, the properties of the binder change—the glass transition temperature decreases while the spin-spin relaxation times and the rate constants of thermal degradation increase, a result that is due to an increase in the length and molecular mobility of interjunction chains in modified samples.

Crystallization Behaviour and Mechanical Properties of Polypropylene Copolymer/Silicon Dioxide Nanocomposites

Polypropylene copolymer (co-PP)/silicon dioxide (SiO2) nanocomposites were prepared by melt extrusion in a twin-screw extruder. The isothermal crystallization behaviour of co-PP/SiO2 composites was investigated by differential scanning calorimetry. The SiO2 restricted the mobility of the co-PP molecular chains and retarded the crystallization of the co-PP component in the co-PP/SiO2 composites. A small amount of SiO2 (3 phr) could increase the tensile strength and elongation at break of the co-PP/SiO2 composites, and a high loading of SiO2 could decrease the tensile strength and elongation at break. Results of thermogravimetric analysis indicated that a small amount of SiO2 could greatly improve the thermal stability.

Investigation of soft segments of thermoplastic polyurethane by NMR, differential scanning calorimetry and rebound resilience

The microscopic and macroscopic properties of a series of thermoplastic polyurethane (TPU) samples with different content in the hard segments and different molecular weight of the soft segments were investigated. Proton NMR transverse magnetization relaxation, DSC and rebound resilience techniques were used to characterize their molecular chain mobility, phase composition, glass transition temperature and angle of rebound. The increase of the hard segments content at the same molecular weight soft segments leads to an increase of the glass transition temperature as determined by DSC and to a decrease of the angle of rebound as determined by rebound resilience. These quantities can be correlated to the decrease in the effective transverse relaxation rates of the soft segments and to the increase of the relative fraction of the hard segments as determined by NMR. By increasing the molecular weight of the soft segments at the same content of the hard segments, the glass transition temperature and the angle of rebound decrease and the effective transverse relaxation time of the soft phase increases.

The linear viscoelastic properties of copolypropylene–clay nanocomposites

AbstractThe linear viscoelastic properties of copolypropylene (cPP)–clay nanocomposites (cPPCNs) prepared by melt intercalating with different amounts of clay were extensively examined by rheological measurements. Meanwhile, the clay effects on the cPP confinements were first estimated by calculating the activation energy of different cPP moving units, including the whole molecular chain, the chain segment, and smaller unit such as chain link. The results showed that the stability of cPPCNs melts wrecked when the clay loading was above 5 wt %. An increase in clay loading of cPPCNs gave rise to a strong low frequency solid‐like response (G′ > G″). Unlike the matrix polymer, cPPCN5 (with 5 wt % clay) exhibited a relaxation plateau as relaxation time prolonged above 100 s, and displayed a maximal linear modulus. The variations of the activation energy of different cPP moving units revealed that the mobility of cPP molecular chains was restricted by clay layers, while these restrictions were not only related to the clay loadings but also largely depended on the clay dispersion status in the matrix. The motions of cPP chain segments were greatly limited at 3–5 wt % loading of clay, but drastically activated with the addition of 7 wt % clay due to the increasing stacks of clay layers within the matrix. However, it was found that the presence of clay had little effect on the mobility of small cPP moving units such as chain links. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 99: 1523–1529, 2006