Non-destructive evaluation of crystallinity and chemical composition by Raman spectroscopy in hydroxyapatite-coated implants

MicroRaman measurements have been performed on a commercially available plasma sprayed hydroxyapatite-coated titanium implant. A double-band structure in the ν₁ vibration mode was clearly identified and attributed to the presence of β-tricalcium phosphate at the metal substrate–hydroxyapatite interface. β-tricalcium phosphate probably results from the specific crystallization mode of the molten hydroxyapatite particles due to rapid cooling during the plasma spray process. The presence of β-tricalcium phosphate can explain the dissolution of the hydroxyapatite coating when exposed to the body fluid for a long period of time due to the high solubility of β-tricalcium phosphate in acidic medium.     

Supermolecular structure of isotactic polypropylene

The crystalline structure, spherulitic crystallization and melting behaviour of isotactic polypropylene (iPP) is comprehensively reviewed, illustrated and discussed. It is demonstrated and summarized how the nucleation, development and growth of the different spherulites depend on the crystallization and melting conditions both in quiescent and sheared melt. Based on the results the microtexture development during real processing conditions is elucidated for selected examples. Several subjects of intense debate on the above topics are clarified using evidence from polarized optical micrography and differential scanning calorimetry.     

A first principles investigation of isotactic polypropylene

Bulk isotactic polypropylene in the α form was studied using density functional theory-based computations. The computed physical structure of this system is in excellent agreement with available experimental data. The electronic band structure, ionization potential, and electron affinity were also determined. The impact of various types of chemical imperfections (including double bond, hydroxyl, and carbonyl defects) on the electronic structure of bulk isotactic polypropylene was considered. The carbonyl defect was found to cause the most significant impact, resulting in the deepest electron and hole traps.     

Microhardness of quenched and annealed isotactic polypropylene

The influence of molecular weight on the microhardness of quenched and subsequently annealed isotactic PP is shown. A clear dependence of microhardness on molecular weight and annealing temperature was detected. Even in the quenched state, where it was difficult to detect morphological differences between the materials, microhardness shows differences. In all states, quenched and annealed, the lower molecular weight samples have the higher hardness values. Up to an annealing temperature of 70 °C the hardness increases only slightly in all samples, above 80 °C a more pronounced increase was observed. For the microhardness of the samples annealed at 140 °C the ratio of the amorphous to the crystalline length is the dominating morphological parameter.     

Non-linear viscoelasticity and viscoplasticity of isotactic polypropylene

Observations are reported in tensile tests with constant cross-head speeds (ranging from 5 to 200 mm/min), relaxation tests (at strains from 0.02 to 0.08), creep tests (at stresses from 15.0 to 25.0 MPa) and recovery tests (after straining up to the maximal strains ranging from 0.04 to 0.12 and subsequent retraction) on isotactic polypropylene at room temperature. A constitutive model is derived for the time- and rate-dependent responses of a semicrystalline polymer at isothermal deformation with small strains. A polymer is treated as an equivalent heterogeneous network of chains bridged by temporary junctions (entanglements, physical cross-links and lamellar blocks). The network is thought of as an ensemble of meso-regions linked with each other. The viscoelastic behavior of the ensemble reflects thermally-induced rearrangement of strands (separation of active strands from temporary junctions and merging of dangling strands with the network). To describe the viscoplastic response, the entire plastic deformation is split into the sum of two components: one of them is associated with sliding of junctions in the non-affine network of chains, while the other accounts for coarse slip and fragmentation of lamellar blocks. Stress–strain relations and kinetic equations for the plastic strains are developed by using the laws of thermodynamics. The constitutive equations involve five material constants that are found by fitting the observations. Fair agreement is demonstrated between the experimental data and the results of numerical simulation.     

Fracture behaviour of virgin and recycled isotactic polypropylene

Fracture behaviour of virgin and six times recycled isotactic polypropylene (PP) has been studied. Instrumented Charpy impact tests have been carried out to characterise the fracture parameters and scanning electron microscopy was used to study the fracture surfaces. Recycled PP presents slightly smaller spherulites and lower fracture toughness than virgin one. Fractography analysis reveals that crazing is the dominant fracture micromechanism for both materials, and that the difference in fracture toughness is a consequence of the smaller plastically deformed volume at the notch tip of the recycled polypropylene.     

Viscoelastic behaviour during the crystallisation of isotactic polypropylene

Morphology and viscoelastic behaviour during the initial stages of crystallisation of isotactic polypropylene were explored as a function of time and angular frequency by light microscopy and dynamic oscillatory rheology. Results were evaluated according to the Krieger-Dougherty and Palierne models for viscoelastic suspensions of spheres. The data obtained from light microscopy were introduced in the rheological models reproducing quite well the viscoelastic response during crystallisation. The Palierne model was able to describe the behaviour of the system, though it was not possible to observe all the model’s features due to a limited angular frequency range. Further, at high filler contents, an ‘equilibrium’ modulus needs to be introduced for the model to fit the experimental data. The exponent required to model the changes occurring in the ‘equilibrium’ modulus over time resembles that of chemical gelation more than physical gelation.     

Crystallization behaviour of isotactic polypropylene blended withtrans-octenylene rubber

The crystallization behaviour of isotactic polypropylene (iPP) blended withtrans-octenylene rubber (TOR) has been investigated by optical microscopy. It is found that crystallization kinetical parameters like nucleation densities, Avrami exponents and spherulitic growth rates are strongly dependent on the TOR concentration in the blend. While at 10% TOR content the nucleation density passes through a maximum, both the Avrami exponent and the spherulitic growth rate are minimal. Due to an increased dispersion of TOR in iPP at 10% TOR concentration and the subsequent formation of interfaces, the nucleation changes from preferentially homogeneous to preferentially heterogeneous. The concentration oftrans double bonds in the TOR chain has no influence on the crystallization behaviour of the samples.     

Microstructure and annealing behaviour of cold-drawn isotactic polypropylene

Isotactic polypropylene tensile bars were cold-drawn at room temperature and subsequently annealed for various times at temperatures ranging from 50 to 155° C. The material was examined at room temperature in the as-drawn state at several stages of annealing. SAXS, density and mechanical loss data were obtained. Furthermore, thin films were cast. These films were drawn at –196° C and subsequently examined in the electron microscope at –120° C and at higher annealing temperatures. SAXS results for lower temperature annealing showed increases in the intensity of the small-angle Bragg hump with no change in position. High temperature annealing produced a very large intensity increase. In no case did the density of the material show a large increase. Electron microscopy indicated a microstructureless material in the as-drawn state. Annealing at low temperatures produced a fibrous morphology with no observable density modulation in the draw direction. High temperature annealing produced a lamellar microstructure with normal, stepwise density modulation. Dynamical mechanical loss curves exhibited no or little relaxation, except after high temperature annealing. On the basis of these observations, a microstructural model is proposed. The model suggests a very highly defective crystal or paracrystal in the as-drawn state. Low temperature annealing promotes a fibrillar, fringed micellar morphology, in which crystalline and amorphous regions are not clearly delineated. At higher annealing temperatures, a lamellar, two-phase microstructure is produced.On leave from Universität des Saarlandes, 66 Saarbrücken, West Germany.     

Vibration-dependent morphology and crystal structure of isotactic polypropylene

A small homemade device was used to study the influence of mechanical vibration on the crystal structure and morphology of isotactic polypropylene (iPP) under different melting temperatures, vibration times, vibration frequencies, and cooling rates. The crystallite size, crystal structure, and crystallinity of iPP under or without vibration treatment were investigated by means of differential scanning calorimetry (DSC), wide angle X-ray diffraction (WAXD), and polarized microscopy observation (PLM). The crystallization of iPP varied with the length of vibration time, vibration frequency, cooling rate, and melt temperature. Compared with the data of conventional samples measured by DSC, vibration could increase the crystallinity of iPP, make melting peak of α-crystal move toward higher temperature and make that of β-crystal shift to lower temperature. Meanwhile, WAXD measurements showed that the vibration could reduce the content of β-crystal evidently, particularly at the lower vibration frequency, lower cooling rate, and higher melting temperature. Furthermore, PLM measurements showed that the vibration made the spherulite size smaller.     

Estimation of spatial averaging of temperatures from coherent anti-Stokes Raman spectroscopy

Spatial averaging is a potential problem in the application of coherent anti-Stokes Raman spectroscopy (CARS) to combustion diagnostics when varying temperatures and composition are present at spatial scales smaller than the typical 1-2-mm spatial resolution of CARS. The observed CARS spectrum is then a mixture of the hot and cold components. We show that simulated, spatially averaged spectra, generated by the incoherent addition of intensities, can be significantly different from those obtained by the coherent addition of the electric field amplitudes of the component spectra. The analyses of these simulated, spatially averaged CARS spectra demonstrate that the use of theoretical CARS spectra, generated by the addition of intensities of the hot and cold components of a binary gas mixture, can lead to errors in the estimated flame temperatures.     

Microstructure of quenched and annealed films of isotactic polypropylene

The Microstructure of quenched and annealed iPP films was investigated by means of differential scanning calorimetry (DSC), density measurements, wide-angle X-ray diffraction (WAXD) and dynamic mechanical spectrometry (DMS). It was found that quenched iPP can be described as a biphasic material constituted of an amorphous phase strongly cross-linked by many crystalline entities exhibiting both small size and very low degree of perfection. Such microcrystallites act as true physical ties of the amorphous phase. On increasing the annealing temperature from 20 °C (quenched film) to 160 °C, the crystallinity ratio first remained constant for annealing temperatures between 20 and 93 °C and then it increased. Subsequently, both size and degree of perfection of crystalline entities progressively increased and tended towards the characteristics of the monoclinic phase. This resulted in a progressive decrease in the physical cross-linking degree of the amorphous phase, even for the samples exhibiting the highest crystallinity ratio.     

等规聚丙烯/豆油溶液体系的结晶过程研究

采用DSC法对等规聚丙烯(iPP)／豆油溶液的非等温结晶过程进行了研究．研究了聚丙烯浓度和降温速率对结晶温度的影响,结晶温度随降温速率升高而下降,随iPP含量增加略有上升,用自制热台在自然降温条件下对聚丙烯／豆油溶液的浊点进行了测定,结合DSC法的测定结果,绘制了聚丙烯／豆油体系的非平衡相图．另外研究了成核剂对结晶温度的影响,研究发现加入成核剂后iPP／豆油体系的结晶温度提高了15℃以上．     

Compatibility and morphology of blends of isotactic and atactic polypropylene

The compatibility and morphology of blends of isotactic and atactic polypropylene have been studied by several means: X-ray scattering, differential scanning calorimetry, and electron microscopy. It was found that the atactic polymer was located mainly inside the spherulites of the isotactic polypropylene on a scale approximately equal to that of the crystalline lamellae. This means that these two polymers were more intimately mixed than are blends of polypropylene and ethylene-propylene copolymer, in which the location of the copolymer is unrelated to the spherulite structure. This difference can be explained by the fact that atactic and isotactic polypropylene are miscible in the melt, whereas polypropylene and ethylene-propylene copolymer are not.