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Semicrystalline Polymers (semicrystalline + polymer)

Distribution by Scientific Domains

Polymers and Materials Science	87%
Chemistry	12%

Selected Abstracts

High-Throughput Screening of the Influence of Thermal Treatment on the Mechanical Properties of Semicrystalline Polymers: A Case Study for iPP

MACROMOLECULAR RAPID COMMUNICATIONS, Issue 1 2004
Konrad Schneider
Abstract Summary: High-throughput screening is a convenient tool to determine the influence of parameters, such as composition or processing conditions on certain materials' properties. In the present study, iPP was used to construct a combinatorial library made from a processing temperature gradient requiring only a minimised amount of material. Clear changes in the crystalline modification and crystal morphology of the iPP, and their impact on mechanical properties have been identified. The construction of a combinatorial library to study the effect of thermal history upon the properties of polymers. [source]

Triple-Shape Polymeric Composites (TSPCs)

ADVANCED FUNCTIONAL MATERIALS, Issue 16 2010
Xiaofan Luo
Abstract In this paper, the fabrication and characterization of triple-shape polymeric composites (TSPCs) that, unlike traditional shape memory polymers (SMPs), are capable of fixing two temporary shapes and recovering sequentially from the first temporary shape (shape 1) to the second temporary shape (shape 2), and eventually to the permanent shape (shape 3) upon heating, are reported. This is technically achieved by incorporating non-woven thermoplastic fibers (average diameter ,760 nm) of a low- Tm semicrystalline polymer into a Tg -based SMP matrix. The resulting composites display two well-separated transitions, one from the glass transition of the matrix and the other from the melting of the fibers, which are subsequently used for the fixing/recovery of two temporary shapes. Three thermomechanical programming processes with different shape fixing protocols are proposed and explored. The intrinsic versatility of this composite approach enables an unprecedented large degree of design flexibility for functional triple-shape polymers and systems. [source]

Online pressure,volume,temperature measurements of polypropylene using a testing mold to simulate the injection-molding process

JOURNAL OF APPLIED POLYMER SCIENCE, Issue 1 2010
Jian Wang
Abstract To obtain accurate prediction of service performance and service life of polymers and to optimize the processing parameters, a modified online measurement was used to measure the pressure,volume,temperature (PVT) properties of polymers under certain processing conditions. The measurement was based on an injection molding machine, and it was used to obtain the PVT data of polymers directly with a special testing mold under normal processing conditions. The PVT properties of a semicrystalline polymer, polypropylene, were measured through both an online testing mold and a conventional piston,die dilatometer. The PVT properties were correlated by a modified two-domain Tait equation of state. The differences between the two groups of PVT data measured were investigated, and relative differences, especially in the rubbery state because of different cooling or heating measuring modes and sample forms, were observed. Numerical simulations of injection-molding processes were carried out by Moldflow software with both of the types of PVT data. The resulting online PVT data exhibited improvement in the accurate prediction of shrinkage and warpage. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010 [source]

Synthesis and Characterization of a Novel Degradable Aliphatic Polyester that Contains Monomeric Lactate Sequences

MACROMOLECULAR RAPID COMMUNICATIONS, Issue 8 2006
Congming Xiao
Abstract Summary: A novel degradable aliphatic polyester that contains monomeric lactate sequences is synthesized via melt-polycondensation of ethylene glycol lactate diol (EGLD) with succinic anhydride without the use of catalyst. The structure of the EGLD precursor and the polyester are verified with FT-IR and 1H NMR spectra. Gel permeation chromatography reveals that the weight-average molecular weight of the polyester is 5.5,×,104 with a polydispersity index (PDI) of 1.7. Differential scanning calorimetry profiles reveal that the polyester is a semicrystalline polymer with a glass transition temperature of ,12,°C and melting temperature of 101,°C. The weight loss percentage of the polyester after immersing for 208 d in active sludge is 2.7%, which suggests degradation has occurred. The synthesis route of the polyester synthesized here (see inset for structure). [source]

Strain-Controlled Tensile Deformation Behavior and Relaxation Properties of Isotactic Poly(1-butene) and Its Ethylene Copolymers

MACROMOLECULAR SYMPOSIA, Issue 1 2004
Mahmoud Al-Hussein
Abstract The tensile deformation behaviour of poly(1-butene) and two of its ethylene copoloymers was studied at room temperature. This was done by investigating true stress-strain curves at constant strain rates, elastic recovery and stress relaxation properties and in-situ WAXS patterns during the deformation process. As for a series of semicrystalline polymers in previous studies, a strain-controlled deformation behaviour was found. The differential compliance, the recovery properties and the stress relaxation curves changed simultaneously at well-defined points. The strains at which these points occurred along the true stress-strain remained constant for the different samples despite their different percentage crystallinities. The well-defined way in which the different samples respond to external stresses complies with the granular substructure of the crystalline lamellae in a semicrystalline polymer. [source]

Conventional and nanometric nucleating agents in poly(,-caprolactone) foaming: Crystals vs. bubbles nucleation

POLYMER ENGINEERING & SCIENCE, Issue 2 2008
Carlo Marrazzo
The aim of this article was to investigate the nucleating ability of different nucleating agents for the foaming of poly(,-caprolactone), a biodegradable, semicrystalline polymer. In particular, the efficiency of the nucleating agent in inducing the formation of the gaseous phase has been compared to the efficiency in inducing the formation of the crystalline phase. In effect, in foaming of semicrystalline polymers, bubble nucleation and crystal nucleation are concurrent and somehow interacting phenomena. Here, these two aspects have been evidenced and clarified. Foams were prepared by using a batch process with the pressure quench method, with nitrogen and carbon dioxide as the blowing agents. Conventional and novel nucleating agents were used: talc has been compared to several novel nanometric particles of different geometries and dimensions, such as titanium dioxide and alumina powders, exfoliated and intercalated clays, and carbon nanotubes. Foam densities and morphologies, in terms of number of cells per initial unit volume, were measured and found to depend both on crystalline phase nucleation and gaseous phase nucleation. In fact, the different nucleating agents, depending on shape, dimension, and surface functionalization, selectively nucleated the crystallites and/or the bubbles, affecting, respectively, bubble growth (and, hence, final foam density) and bubble nucleation (and, hence, cell number density,morphology). POLYM. ENG. SCI., 2008. © 2007 Society of Plastics Engineers [source]

A uniform phenomenological constitutive model for glassy and semicrystalline polymers

POLYMER ENGINEERING & SCIENCE, Issue 8 2001
Y. Duan
A phenomenological constitutive model is proposed on the basis of four models: the Johnson-Cook model, the G'Sell-Jonas model, the Matsuoka model, and the Brooks model. The proposed constitutive model has a concise expression of stress dependence on strain, strain rate and temperature. It is capable of uniformly describing the entire range of deformation behavior of glassy and semicrystalline polymers, especially the intrinsic strain softening and subsequent orientation hardening of glassy polymers. At least three experimental stress-strain curves including variation with strain rate and temperature are needed to calibrate the eight material coefficients. Sequential calibration procedures of the eight material coefficients are given in detail. Predictions from the proposed constitutive model are compared with experimental data of two glassy polymers, polymethyl-methacrylate and polycarbonate under various deformation conditions, and with that of the G'Sell-Jonas model for polyamide 12, a semicrystalline polymer. [source]

Hydroxyapatite as a filler for biosynthetic PHB homopolymer and P(HB,HV) copolymers

POLYMER INTERNATIONAL, Issue 7 2003
Antje Bergmann
Abstract This paper deals with some of the fundamental problems encountered when using a semicrystalline polymer as the matrix phase for a particulate-filled composite. As our model system we adopted poly-(R)-3-hydroxybutyrate, PHB, and two copolymers of (R)-3-hydroxybutyrate and (R)-3-hydroxyvalerate, P(HB,HV), for the matrix phase, and the mineral calcium hydroxyapatite as a particulate filler. The structure and properties of compression-moulded films of various compositions were investigated by polarized light microscopy, wide-angle X-ray scattering and mechanical testing. It was found that the degree of crystallinity of the matrix was lower in filled samples, and that the spherulitic crystallization of the matrix appeared to cause the filler particles to form agglomerates, which would not be as effective a reinforcement as finely dispersed primary filler particles. The tensile strength, strain-to-break and tensile modulus of samples of different compositions were analysed using well-known theories for composite behaviour. Copyright © 2003 Society of Chemical Industry [source]

Bimolecular Crystals of Fullerenes in Conjugated Polymers and the Implications of Molecular Mixing for Solar Cells

ADVANCED FUNCTIONAL MATERIALS, Issue 8 2009
A. C. Mayer
The performance of polymer:fullerene bulk heterojunction solar cells is heavily influenced by the interpenetrating nanostructure formed by the two semiconductors because the size of the phases, the nature of the interface, and molecular packing affect exciton dissociation, recombination, and charge transport. Here, X-ray diffraction is used to demonstrate the formation of stable, well-ordered bimolecular crystals of fullerene intercalated between the side-chains of the semiconducting polymer poly(2,5-bis(3-tetradecylthiophen-2-yl)thieno[3,2- b]thiophene. It is shown that fullerene intercalation is general and is likely to occur in blends with both amorphous and semicrystalline polymers when there is enough free volume between the side-chains to accommodate the fullerene molecule. These findings offer explanations for why luminescence is completely quenched in crystals much larger than exciton diffusion lengths, how the hole mobility of poly(2-methoxy-5-(3,,7,-dimethyloxy)-p-phylene vinylene) increases by over 2 orders of magnitude when blended with fullerene derivatives, and why large-scale phase separation occurs in some polymer:fullerene blend ratios while thermodynamically stable mixing on the molecular scale occurs for others. Furthermore, it is shown that intercalation of fullerenes between side chains mostly determines the optimum polymer:fullerene blending ratios. These discoveries suggest a method of intentionally designing bimolecular crystals and tuning their properties to create novel materials for photovoltaic and other applications. [source]

The continuous cooling transformation (CCT) as a flexible tool to investigate polymer crystallization under processing conditions

ADVANCES IN POLYMER TECHNOLOGY, Issue 2 2009
V. Brucato
Abstract An experimental route for investigating polymer crystallization over a wide range of cooling rates (from 0.01 to 1000°C/s) and pressures (from 0.1 to 40 MPa) is illustrated, using a method that recalls the approach adopted in metallurgy for studying structure development in metals. Two types of experimental setup were used, namely an apparatus for fast cooling of thin films (100,200 ,m thick) at various cooling rates under atmospheric pressure and a device (based on a on-purpose modified injection molding machine) for quenching massive samples (about 1,2 cm3) under hydrostatic pressure fields. In both cases, ex situ characterization experiments were carried out to probe the resulting structure, using techniques such as density measurements and wide-angle x-ray diffraction (WAXD) patterns. The cooling mechanism and temperature distribution across the sample thickness were analyzed. Results show that the final structure is determined only by the imposed thermal history and pressure. Experimental results for isotactic polypropylene (iPP), poly(ethylene terephthalate) (PET), polyamide 6 (PA6), and syndiotactic polystyrene (sPS) are reported, showing the reliability of this experimental approach to assess not only quantitative information but also a qualitative description of the crystallization behavior of different classes of semicrystalline polymers. The present study gives an opportunity to evaluate how the combined effect of the cooling rate and pressure influences the crystallization kinetics for various classes of polymer of commercial interest. An increase in the cooling rate translates into a decrease in crystallinity and density, which both experience a sudden drop around the specific "crystallizability" (or "critical cooling rate") of the material examined. The exception is sPS where competition among the various crystalline modifications determines a minimum in the plot of density vs. cooling rate. As for the effect of pressure, iPP exhibits a "negative dependence" of crystallization kinetics upon pressure, with a decrease of density and degree of crystallinity with increasing pressure, owing to kinetic constraints. PA6 and PET, on the other hand, due to thermodynamic factors resulting in an increase in Tm with pressure, exhibits a "positive dependence" of crystallization kinetics upon pressure. Finally, recent original results concerning sPS have shown that the minimum in the density vs. cooling rate curve shifts toward larger cooling rates upon increasing pressure. © 2009 Wiley Periodicals, Inc. Adv Polym Techn 28:86,119, 2009; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/adv.20151 [source]

Factors affecting the formation of fingering in water-assisted injection-molded thermoplastics

ADVANCES IN POLYMER TECHNOLOGY, Issue 2 2006
Shih-Jung Liu
Abstract Water-assisted injection-molding technology has received extensive attention in recent years, due to the lightweight of plastic parts, relatively low-resin cost per part, faster cycle time, and flexibility in the design and manufacture. However, there are still some unsolved problems that confound the overall success of this technology. One of these is the water "fingering" phenomenon, in which the water bubbles penetrate outside designed water channels and form finger-shape branches. This study has investigated the effects of various processing parameters on the formation of fingering in water-assisted injection-molded thermoplastic parts. Both amorphous and semicrystalline polymers were used to mold the parts. The influence of water channel geometry, including aspect ratio and fillet geometry, on the fingering was also investigated. It was found that water-assisted injection-molded amorphous materials gave less fingering, while molded semicrystalline parts gave more fingering when compared to those molded by gas-assisted injection molding. For the water channels used in this study, the channels with a rib on the top produced parts with the least water fingering. Water fingering in molded parts decreases with the height-to-thickness ratio of the channels. The water pressure, water injection delay time and short-shot size were found to be the principal parameters affecting the formation of water fingering. In addition, a numerical simulation based on the transient heat conduction model was also carried out to help better explain the mechanism for the formation of fingering in water-assisted injection-molded thermoplastics. © 2006 Wiley Periodicals, Inc. Adv Polym Techn 25: 98,108, 2006; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/adv.20062 [source]

Small-angle energy-dispersive X-ray scattering using a laboratory-based diffractometer with a conventional source

JOURNAL OF APPLIED CRYSTALLOGRAPHY, Issue 2 2007
Giuseppe Portale
The use of polychromatic Bremsstrahlung X-rays generated by commercial tubes for energy-dispersive small-angle scattering measurements has not been extensively discussed in the literature, mainly because of some difficulties associated with it. If a suitable experimental setup is chosen and concomitant phenomena are taken into account for correcting the observed X-ray patterns, energy-dispersive small-angle X-ray scattering (SAXS) may become an interesting alternative to conventional measurements based on monochromatic beams. Energy-dispersive SAXS experiments carried out on protein solutions, micelles, semicrystalline polymers and catalytic systems are discussed to illustrate the new opportunities offered by this technique as well as its limitations. [source]

Effect of interfacial strengthening in blends of reclaimed rubber and polypropylene

JOURNAL OF APPLIED POLYMER SCIENCE, Issue 2 2010
S.-H. Zhu
Abstract Thermoplastic vulcanizates (TPVs) were prepared from polypropylene (PP) and reclaimed ground tire rubber crumbs. Three types of interfacial strengthening agents,degraded PP, hydrosilylated PP, and hydrosilylated PP grafted onto styrene,butadiene rubber,were prepared in melt via a stepwise series of reactions and employed to generate various degrees of interfacial adhesion in the aforementioned blends. The incorporation of the interfacial agents resulted in improvements in the mechanical properties of these TPVs, and the rubber particle size remained constant. The PP chain length and the functional groups present in the interfacial agents affected the magnitude of the improvement in the mechanical properties. The interfacial agents were primarily present on the surface of the rubber particles in the blends, as shown by energy-dispersive X-ray spectra. These interfacial agents in the PP/rubber crumb blends led to a unique preyield kink in their stress,strain curves, a plateau, or a sharp turning point in the region of approximately 3% elongation and approximately 4-MPa stress. These kinks were interpreted similarly to the cold flow of semicrystalline polymers in tension. The addition of the interfacial modifiers decreased the shear viscosity and increased the entrance pressure drop in flow through capillary dies, and this was attributed to changes in the elongational viscosity of the blends. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010 [source]

Linear polyurethanes made from naturally occurring tartaric acid

JOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 9 2009
Romina Marín
Abstract Naturally occurring tartaric acid was used as raw material for the synthesis of novel linear polyurethanes (PURs) bearing two carboxylate side-groups in the repeating unit. Aliphatic and aromatic PURs were obtained by reaction in solution of alkyl and benzyl tartrates with hexamethylene diisocyanate and 4,4,-methylene-bis(phenyl isocyanate), respectively. All the novel PURs were thermally stable and optically active. The aliphatic carboxylate-containing PURs had Mw in the 40,70 kDa range, with PD between 2.1 and 2.5; all were semicrystalline polymers with melting temperatures between 100 and 150 °C and Tg in the 50,80 °C range. The aromatic PURs were amorphous materials with molecular weights between 18 kDa and 25 kDa and Tg above 130 °C. Hydrogenolysis of the PUR made from hexamethylene diisocyanate and benzyl tartrate yielded PURs containing up to 40% of free carboxylic side-groups. The tartrate-derived PURs displayed enhanced sensitivity to hydrolysis compared with their unsubstituted 2,6-PUR homologs. The PURs bearing free carboxylic groups were unique in being degraded by water upon incubation under physiological conditions. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 2391,2407, 2009 [source]

Application of Fractionation Techniques to the Study of Olefin Polymerization Kinetics and Polymer Degradation

MACROMOLECULAR SYMPOSIA, Issue 1 2007
Hisayuki Nakatani
Abstract Summary: Temperature rising elution fractionation (TREF) has been regarded as a powerful technique for study of semicrystalline polymers. In this paper, two examples of unique applications of TREF were introduced. One was the study on the influence of extraction of internal donor on the variation of isospecific active sites of a MgCl2 - supported Ziegler catalyst, and the other was the estimation of the relationship between polymer micro-tacticity and degradation rate of isotactic polypropylene (iPP). The former example revealed the conversion from high to low isospecific site by the extraction of internal donors, whereas the latter showed a negative correlation between the level of isotacticity and the degradation rate. These results demonstrated that TREF was useful in these research applications. [source]

Strain-Controlled Tensile Deformation Behavior and Relaxation Properties of Isotactic Poly(1-butene) and Its Ethylene Copolymers

Conventional and nanometric nucleating agents in poly(,-caprolactone) foaming: Crystals vs. bubbles nucleation

Theoretical and experimental studies of anisotropic shrinkage in injection moldings of semicrystalline polymers

POLYMER ENGINEERING & SCIENCE, Issue 6 2006
Keehae Kwon
A novel approach to predict anisotropic shrinkage of semicrystalline polymers in injection moldings was proposed using flow-induced crystallization, frozen-in molecular orientation, elastic recovery, and PVT equation of state. The anisotropic thermal expansion and compressibility affected by the frozen-in orientation function and the elastic recovery that was not frozen during moldings were introduced to obtain the in-plane anisotropic shrinkages. The frozen-in orientation function was calculated from amorphous and crystalline contributions. The amorphous contribution was based on the frozen-in and intrinsic amorphous birefringence, whereas the crystalline contribution was based on the crystalline orientation function, which was determined from the elastic recovery and intrinsic crystalline birefringence. To model the elastic recovery and frozen-in stresses related to birefringence during molding process, a nonlinear viscoelastic constitutive equation was used with temperature- and crystallinity-dependent viscosity and relaxation time. Occurrence of the flow-induced crystallization was introduced through the elevation of melting temperature affected by entropy production during flow of the viscoelastic melt. Kinetics of the crystallization was modeled using Nakamura and Hoffman-Lauritzen equations with the rate constant affected by the elevated melting temperature. Numerous injection molding runs on polypropylene of various molecular weights were carried out by varying the packing time, flow rate, melt temperature, and mold temperature. The anisotropic shrinkage of the moldings was measured. Comparison of the experimental and simulated results indicated a good predictive capability of the proposed approach. POLYM. ENG. SCI., 46:712,728, 2006. © 2006 Society of Plastics Engineers [source]

The effect of annealing on the nonlinear viscoelastic response of isotactic polypropylene

POLYMER ENGINEERING & SCIENCE, Issue 4 2003
Aleksey D. Drozdov
Three series of tensile relaxation tests are performed on isotactic polypropylene at room temperature in the vicinity of the yield point. In the first series of experiments, injection-molded samples are used without thermal pre-treatment. In the second and third series, the specimens are annealed at 130°C for 4 and 24 hours, respectively. Constitutive equations are derived for the time-dependent response of semicrystalline polymers at isothermal loading with small strains. A polymer is treated as an equivalent temporary network of macromolecules bridged by junctions (physical cross-links, entanglements and crystalline lamellae). Under loading, junctions slide with respect to their positions in the bulk material (which reflects the viscoplastic behavior), whereas active strands separate from their junctions and dangling strands merge with the network at random times (which reflects the viscoelastic response). The network is thought of as an ensemble of meso-regions (MRs) with various activation energies for detachment of chains from temporary nodes. Adjustable parameters in the stress-strain relations are found by fitting the observations. The experimental data demonstrate that the relaxation spectrum (characterized by the distribution of MRs with various potential energies) is independent of mechanical factors, but is altered at annealing. For specimens not subjected to thermal treatment, the growth of longitudinal strain does not affect the volume fraction of active MRs and the attempt rate for detachment of chains from their junctions. For annealed samples, the concentration of active MRs increases and the attempt rate decreases with strain. These changes in the time-dependent response are attributed to broadening of the distribution of strengths of lamellae at annealing. [source]

A uniform phenomenological constitutive model for glassy and semicrystalline polymers

Toughening effects of poly(butylene terephthalate) with blocked isocyanate-functionalized poly(ethylene octene)

POLYMER INTERNATIONAL, Issue 8 2009
Ligang Yin
Abstract BACKGROUND: Blocked isocyanate-functionalized polyolefins have great potential for use in semicrystalline polymer blends to obtain toughened polymers. In this study, poly(butylene terephthalate) (PBT) was blended with allyl N -[2-methyl-4-(2-oxohexahydroazepine-1-carboxamido)phenyl] carbamate-functionalized poly(ethylene octene) (POE- g -AMPC). RESULTS: New peaks at 2272 and 1720 cm,1, corresponding to the stretching vibrations of NCO and the carbonyl of NHCON, respectively, in AMPC, appeared in the infrared spectrum of POE- g -AMPC. Both rheological and X-ray photoelectron spectroscopy results indicated a new copolymer was formed in the reactive blends. Compared to uncompatibilized PBT/POE blends, smaller dispersed particle sizes with narrower distribution were found in the compatibilized PBT/POE- g -AMPC blends. There was a marked increase in impact strength by about 10-fold over that of PBT/POE blends with the same rubber content and almost 30-fold higher than that of pure PBT when the POE- g -AMPC content was 25 wt%. CONCLUSION: The blocked isocyanate-functionalized POE is an effective toughener for semicrystalline polymers. Super-toughened PBT blends can be obtained when the POE- g -AMPC content is equal to or more than 15 wt%. Copyright © 2009 Society of Chemical Industry [source]

Thermal properties and non-isothermal crystallization behavior of biodegradable poly(p -dioxanone)/poly(vinyl alcohol) blends

POLYMER INTERNATIONAL, Issue 4 2006
Zhi-Xuan Zhou
Abstract Blends of two biodegradable semicrystalline polymers, poly(p -dioxanone) (PPDO) and poly(vinyl alcohol) (PVA) were prepared with different compositions. The thermal stability, phase morphology and thermal behavior of the blends were studied by using thermogravimetric analysis (TGA), scanning electron microscopy (SEM) and differential scanning calorimetry (DSC). From the TGA data, it can be seen that the addition of PVA improves the thermal stability of PPDO. DSC analysis showed that the glass transition temperature (Tg) and the melting temperature (Tm) of PPDO in the blends were nearly constant and equal to the values for neat PPDO, thus suggesting that PPDO and PVA are immiscible. It was found from the SEM images that the blends were phase-separated, which was consistent with the DSC results. Additionally, non-isothermal crystallization under controlled cooling rates was explored, and the Ozawa theory was employed to describe the non-isothermal crystallization kinetics. Copyright © 2006 Society of Chemical Industry [source]