Evolution of crystallinity and of crystallographic orientation in isotactic polypropylene during rolling and heat treatment

The development of the crystallinity and of the crystallographic orientation of isotactic polypropylene during rolling deformation and subsequent heat treatment is studied. The experiments are conducted by using X-ray diffraction with an area detector. The evolution of crystallographic orientation is tracked by calculating the pole figures and by applying a quantitative 3D texture component fit method. The rolling orientation after a true strain of −1.5 mainly consists of the (0 1 0)[0 0 1], (1 3 0)[0 0 1], and [0 0 1]//RD fiber components (RD: rolling direction). The results reveal that the crystallinity drastically decreases during rolling. We suggest that decrystallization (disaggregation) is a deformation mechanism which takes place as a microscopic alternative to crystallographic intralamellar shear depending on the orientation of the lamellae relative to the imposed deformation tensor. Heat treatment after rolling leads to the recrystallization of amorphous material and to a strong enhancement of the fiber orientation component. The recrystallization orientation is explained in terms of an oriented nucleation mechanism where amorphous material aligns along existing crystalline lamellae blocks which prevailed during the preceding deformation.     

In situ FTIR spectroscopic study of the recently detected low‐temperature‐induced structural changes in isotactic polypropylene

The in situ Fourier transform infrared spectroscopic study of isotactic polypropylene showed that structural changes are induced at liquid nitrogen temperature, and start to show up in the FTIR spectra with heating from ?196 to +200 °C. This structural change leads to the detection of an abnormal behavior in the MIR absorption spectra of the investigated sample. Lowering the temperature brought the chains closer together and so increased the interchain interaction. At ?196 °C splitting of some regularity bands assigned to helical chains within the crystalline region was observed, showing that the regularity of the chains increases because of cooling. Heating the samples from liquid nitrogen temperature caused an opposite conformational disordering, which resulted in the appearance of several new broad bands in the ranges: 600–700, 1614–1640, and 3050–3550 cm^?1. These structural changes might be due to both twisting and folding of the chains, which gave rise to bands assigned to the various bending modes of CH₂ molecules, in addition to the rotational isomers (conformers) resulting from rotation of the vinyl and alkyne end groups. Moreover, our experimental study of the behavior of several regularity bands suggests that at temperatures in the vicinity of +120 °C another high temperature structural change resulting from the disordering of helical sequences in the noncrystalline region takes place. Differential scanning calorimetry thermograms of the thermally treated and an untreated sample were found to confirm the obtained results. © 2005 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 43: 2829–2842, 2005     

Nucleation of crystallization in isotactic polypropylene and polyoxymethylene with poly(tetrafluoroethylene) particles

Nucleation of crystallization of isotactic polypropylene (iPP) and polyoxymethylene (POM) with dispersed submicron particles of another polymer - poly(tetrafluoroethylene) (PTFE) was studied. The polymers were mixed with various contents of PTFE particles, in the range from 0.005 to 0.5 wt.%. iPP and POM with PTFE particles are all-polymer systems with enhanced nucleation of crystallization. PTFE particles with sizes below 300 nm added to POM and iPP efficiently decreased sizes of polycrystalline aggregates. Moreover, nonisothermal crystallization temperature of iPP by increased by up to 14 °C. iPP and POM with PTFE exhibited the elastic modulus slightly higher, by up to 10-13%, than that of the neat polymers. Other mechanical properties remained unchanged, with the exception of reduced elongation at break of POM with PTFE.     

Morphology and properties of isotactic polypropylene/poly(ethylene terephthalate) in situ microfibrillar reinforced blends: Influence of viscosity ratio

In situ microfibrillar reinforced blends based on blends of isotactic polypropylene (iPP) and poly(ethylene terephthalate) (PET) were successfully prepared by a “slit extrusion-hot stretching-quenching” process. Four types of iPP with different apparent viscosity were utilized to investigate the effect of viscosity ratio on the morphology and mechanical properties of PET/iPP microfibrillar blend. The morphological observation shows that the viscosity ratio is closely associated to the size of dispersed phase droplets in the original blends, and accordingly greatly affects the microfibrillation of PET. Lower viscosity ratio is favorable to formation of smaller and more uniform dispersed phase particles, thus leading to finer microfibrils with narrower diameter distribution. Addition of a compatibilizer, poly propylene-grafted-glycidyl methacrylate (PP-g-GMA), can increase the viscosity ratio and decrease the interfacial tension between PET and iPP, which tends to decrease the size of PET phase in the unstretched blends. After stretched, the aspect ratio of PET microfibrils in the compatibilized blends is considerably reduced compared to the uncompatibilized ones. The lower viscosity ratio brought out higher mechanical properties of the microfibrillar blends. Compared to the uncompatibilized microfibrillar blends, the tensile, flexural strength and impact toughness of the compatibilized ones are all improved.     

Molecular deformation mechanisms of isotactic polypropylene in α‐ and β‐crystal forms by FTIR spectroscopy

The orientation behavior of isotactic polypropylene (iPP) in α‐ and β‐crystal form was investigated by rheo‐optical Fourier transformed infrared (FTIR) spectroscopy. This method enabled quantification of the degree of orientation as a feature of structural changes during uniaxial elongation in not only the crystalline phase but also the amorphous one. Molecular orientation mechanisms can be successfully derived from experimental results. Generally, three mechanisms were detected for iPP: (1) interlamellar separation in the amorphous phase, (2) interlamellar slip and lamellar twisting at small elongations, and (3) intralamellar slip at high elongations. The third mechanism was favored by α‐PP, whereas β‐PP favored the second mechanism, which, in fact, was responsible for the different mechanical properties of both materials at the macroscopic level. On the other hand, crystallization conditions may have significantly affected the amorphous orientation. Nevertheless, for both iPP types the chains in the amorphous phase always oriented less than did those in the crystalline phase. © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 4478–4488, 2004     

The use of synchrotron X-ray scattering coupled with in situ mechanical testing for studying deformation and structural change in isotactic polypropylene

The mechanical behaviour of semi-crystalline polymers is greatly influenced by the properties of the crystalline and the amorphous phases. As a result this topic has been the subject of extensive research. However, to date, a comprehensive relationship between the structure and mechanical properties for semi-crystalline polymers has yet to be established. This present study concerns the commissioning of a novel method for in situ data collection during the deformation of polymers. This involves the combination of three different techniques into a single experiment, namely tensile testing, synchrotron radiation wide angle X-ray scattering, and optical microscopy. For this current investigation, three isotactic polypropylene samples have been studied, produced using different thermal treatments. This enables the influence of thermal treatment on the mechanical properties and crystallographic structure to be assessed. The results indicate that tensile properties are influenced by thermal treatment via the relative fraction of -phase material in the sample. As the temperature increases at which thermal treatment takes place, iPP ductility decreases due to the greater rigidity of the increasing -phase content. Differences in crystal strain between the different iPP crystal phases are also observed although the reasons for such differences remain unclear.     

The β‐crystalline form of isotactic polypropylene in blends of isotactic polypropylene and polyamide‐6/clay nanocomposites

Blends of isotactic polypropylene and polyamide‐6/clay nanocomposites (iPP/NPA6) were prepared with an internal batch mixer. A high content of the β‐crystalline form of isotactic polypropylene (β‐iPP) was observed in the injection‐molded samples of the iPP/NPA6 blends, whereas the content of β‐iPP in the iPP/PA6 blends and the iPP/clay composite was low and similar to that of neat iPP. Quiescent melt crystallization was studied by means of wide‐angle X‐ray diffraction, differential scanning calorimetry, and polarized optical microscopy. We found that the significant β‐iPP is not formed during quiescent melt crystallization regardless of whether the sample used was the iPP/NPA6 blend or an NPA6 fiber/iPP composite. Further characterization of the injection‐molded iPP/NPA6 revealed a shear‐induced skin–core distribution of β‐iPP and the formation of β‐iPP in the iPP/NPA6 blends is related to the shear flow field during cavity‐filling. In the presence of clay, the deformation ability of the NPA6 domain is decreased, as evidenced by rheological and morphological studies. It is reasonable that the enhanced relative shear, caused by low deformability of the NPA6 domain in the iPP matrix, is responsible for β‐iPP formation in the iPP/NPA6 blends. © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 3428–3438, 2004     

Temperature dependence of molecular conformation in uniaxially deformed isotactic polypropylene investigated by combination of polarized FTIR spectroscopy and 2D correlation analysis

Evolution of molecular conformation in uniaxially deformed isotactic polypropylene (iPP) as a function of temperature is investigated by time‐resolved polarized Fourier‐transform infrared spectroscopy. It is observed that oriented crystals (microfibrils) induced by deformation possess better thermal stability compared with isotropic spherulites. 2D correlation analysis reveals that the relaxation process of ordered helices in deformed iPP could be divided into two regions referring to the melting of different crystalline structures. No obvious sequential change of ordering conformations observed in low temperature region is attributed to melting of defective or destructed crystals. However, notable sequential changes of helices occur in the high temperature region; interestingly, long helices are more thermally stable than short helices. The central region of microfibrils is suggested to consist of a large amount of long helical bundles, and the short ordering segments are primarily located in the outer lateral surfaces. A physical picture of the conformational distribution in deformation‐induced microfibrils is thus gained. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2015 , 53, 673–684     

In situ FT‐Raman spectroscopic study of the conformational changes occurring in isotactic polypropylene during its melting and crystallization processes

The conformational changes occurring in isotactic polypropylene during the melting and crystallization processes have been carefully investigated using FT‐Raman spectroscopy at temperatures below, at, and above the polymer melting point. Results confirmed the retention of some crystallinity up to +210 °C, which is 50 °C above the melting point. It was found that, at temperatures just above the melting point (1–10 °C), there is still some short range order of at least 12 monomer units long in certain regions of the melt. At 10 °C above the melting point, the short range order drops below 12 monomer units resulting in the disappearance of the Raman band at 841 cm^–1. Vice versa, the experimental measurements show that the iPP melt system is stable when the persistence length of helical sequences is less than 12 monomer units. As soon as the helix length exceeds 12 units, the 3₁ helix conformation extends quickly and then crystallization occurs. These results are discussed in terms of Imai's microphase separation theory and it agreed very well with it. Also, from our observations for correlation splitting, Raman bands related to conformational states were identified. This analysis indicates the existence of three different conformational states at 808, 830, and 841 cm^–1. The 808 cm^–1 band was assigned to helical chains within crystals (representing crystalline phase). The 841 cm^–1 band was shown to be composed of a band at 841 cm^–1, assigned to shorter chains in helical conformation with isomeric defects (representing the isomeric defect phase), and a broader band at 830 cm^–1 assigned to chains in nonhelical conformation (representing the melt‐like amorphous phase). This indicates the detection of a three‐phase structure in iPP, where a third phase could be due to the presence of defect regions within the crystalline region, or due to the presence of an amorphous–crystal interphase. © 2006 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 44: 2173–2182, 2006     

ATR‐FTIR Kretschmann spectroscopy for interfacial studies of a hidden aluminum surface coated with a silane film and epoxy II. Analysis by integrated ATR‐FTIR and EIS during exposure to electrolyte with complementary studies by in situ ATR‐FTIR and in situ IRRAS

The destabilization of the interface between a polymer and a metal surface is of considerable interest in several application areas, including the ongoing research on environmentally friendly pretreatments as a replacement for the Cr(VI)‐containing systems where the understanding of mechanisms and performance of a confined metal/polymer interface is of utmost importance. Processes at hidden interfaces are, however, difficult to analyze in detail and at relevant climatic conditions. This study has been divided in two parts, where the subject of Part I is the surface characterization by ATR‐FTIR Kretschmann and IRRAS spectroscopy of aluminum coated with an amino‐functional silane, and the interfacial analysis by ATR‐FTIR Kretschmann after further application of an epoxy film. This second part describes the interaction between the coated sample and an electrolyte. The analysis is performed by integrated in situ ATR‐FTIR Kretschmann and EIS, which requires model systems with evaporated metal films on an internal reflection element. Complementary analyses were also conducted on substrates in the absence of the metal film, and or in the absence of an epoxy top‐coat, respectively. Changes in the interfacial region were observed and assigned to the water uptake including swelling of the epoxy, and the formation of aluminium oxidation and hydration products. Complementary studies allowed the distinction between water uptake in the silane film and the epoxy, respectively, as well as reformations of the siloxane network. Copyright © 2011 John Wiley & Sons, Ltd.     

Chemical-physical aspects of formation and evolution of phase structure in multi-polymers: Intensity fluctuation, phase structure and its fractal characteristics in blends of isotactic polypropylene with poly(cis-1,4-butadiene) rubber

This paper studies the formation and evolution of phase structure of isotactic polypropylene/poly(cis-1,4-butadiene) (iPP/PcBR) blends during molten and mixing in a visual mixer by on-line analysis of the small angle light back scattering. The density fluctuation of iPP/PcBR blends during molten and mixing is discussed using the integral-intensity Js, of the scattering intensity of the blends. The "invariant" Q, which shows fluctuation of the system, is calculated by data of the small angle light back scattering, and the variation of Q with the blending time, temperature and shear rate during molten and mixing in iPP/PcBR blends is discussed. The structure parameters which characterize dimensions of phase in the blends, as the correlation distance ac, and the average chord lengths of two-phase, as li PP and lP cBR, are calculated by data of scattering intensity. The average diameters dp of dispersed phases are calculated from SEM images. The variation of ac, dp, li PP and lP cBR with the blending time and compositions in the blends during molten and mixing is discussed. The scale law is analyzed to find multi-scale characteristics in this system. The generalized fractal dimension Dp is calculated and the relation of Dp with generalized entropy function is discussed to determine that Dp is state function and the physical significance of Dp is the same as that of the generalized entropy function.     

Use of 9,10-diphenylanthracene as a contrast agent in chemiluminescence imaging: The observation of spreading of oxidative degradation in thin polypropylene films

Thin films of polypropylene were doped with a chemiluminescence (CL) activator, 9,10-diphenylanthracene (DPA), and were thermally oxidised in a CL imaging apparatus to determine whether heterogeneous oxidation processes such as spreading of oxidation could be observed. The presence of DPA resulted in significantly more intense CL images compared with undoped polymer, due to the efficient chemically induced electron exchange luminescence reaction between DPA and hydroperoxides. Hence, the CL images from DPA-doped PP were used to locate the position of hydroperoxides in the oxidising polymer. For thermal oxidation at 150 and 140 °C hydroperoxides were observed to form in localised regions of the films, whilst other areas remained hydroperoxide free. As the oxidation time increased the concentration of hydroperoxides in these areas increased and they were observed to spread to the remainder of the polymer. Time-resolved line maps from the images indicated that zones with high concentration of hydroperoxides travel through the polymer during oxidation. Integrals of CL images from the thermal oxidation of DPA-doped polymers indicated that a significant degree of oxidation had occurred by the end of the “induction period” for a conventional CL-intensity oxidation-time profile. This is a likely reason why spreading of oxidation has not previously been observed for undoped PP films.     

Extent of structural change during the reaction and its relationship to isoselectivity in polypropylene polymerization with ansa-zirconocene/borate catalyst: A computational study

The mechanism of isotactic polypropylene (iPP) polymerization with an (R,R)-ansa-zirconocene/borate catalyst system was analyzed using quantum chemistry (QC) calculations by focusing on the extent of structural change during monomer insertion. The activation energy for migratory insertion, E_a, was compared for four possible reaction paths with regard to monomer coordination, that is, 1,2-re, 1,2-si, 2,1-si, and 2,1-re, until the seventh monomer insertion step, explicitly including a borate anion cocatalyst. This indicated that the 1,2-re path was most favorable, except for the first step, which favored 1,2-si. As far as the first step, the product of 1,2-si is a conformational isomer to that of the 1,2-re path, and the exceptional favorability of 1,2-si does not affect the isoselectivity. These results support previous studies, except that our results address the unexplored seventh insertion step with a borate anion cocatalyst by QC calculations. The isoselectivity correlated with the extent of structural change in the whole system during the reaction. It was proved from our detail analysis that the advantage of 1,2-re with a small E_a is attributed to its smaller structural changes due to low steric repulsion in the system compared with other paths. Conversely, larger repulsion in the systems involved in other paths results in larger structural changes to minimize the structural strain. However, the relaxation appears insufficient due to structural restriction of the enforced four-membered ring transition state structure. A borate anion cocatalyst broke the C₂ symmetry of the electronic structures of zirconocene, resulting in an odd–even E_a frequency for the monomer insertion. Molecular orbital analysis demonstrated that the d–π orbital overlaps can explain the approach direction of the olefin coordination and the bent structure of zirconocene, providing a different viewpoint from previous studies. The potential for catalyst control was discussed based on our results. © 2019 Wiley Periodicals, Inc.     

NOR and nitroxide-based HAS in accelerated photooxidation of carbon-chain polymers; Comparison with secondary HAS: An ESRI and ATR FTIR study

Understanding processes resulting in heterogeneous degradation in polymers is of extreme importance for improving their stabilization and minimizing negative impact of photooxidation on the material properties. We adopted modern physical techniques for studies of spatial distribution of intermediates and products of photodegradation during accelerated ageing of four commodity polymers, polypropylene (PP), polyethylene (PE), polystyrene (PS) and poly(ethylene-co-norbornene) (Topas^®, TP) stabilized with hindered amine stabilizer (HAS). Concentration profiles of nitroxides inside polymer plaques along the direction perpendicular to their surface were determined by electron spin resonance imaging (ESRI) as a function of the duration of the accelerated photooxidation. We present data characterizing stabilization activity of three alkoxyamine derivatives of HAS (Tinuvin^® NOR 123, Tinuvin^® NOR 371, Flamestab^® NOR 116), Chimasorb^® 119 structurally similar to Flamestab^® NOR 116, and nitroxide-based HAS Dastib^® 1045 and compare them with the data characterizing stabilization activity of the secondary HAS (>NH) Tinuvin^® 770. ESRI data are complemented by ATR FTIR spectroscopic detection of oxidation products on the surface and inside the plaques and by data characterizing diffusive optical transmittance of the polymer plaques in the spectral region 280-400 nm (terrestrial range of the solar UV radiation).     

The study of ion transport parameters associated with dissociated cation using EIS model in solid polymer electrolytes (SPEs) based on PVA host polymer: XRD,FTIR, and dielectric properties

Electrical impedance spectroscopy (EIS) model is used to determine ion transport parameters. The transport parameters such as mobility, carrier density and diffusion coefficient of ions are the subject of great interest. The solution cast method is used to fabricate SPEs using polyvinyl alcohol (PVA) loaded with different amounts of sodium iodide (NaI). XRD deconvolution is used to separate the crystalline phase from amorphous phase. The degree of crystallinity is reduced with an increased amount of NaI. FTIR is used to investigate the polymer/salt interactions. To find out the circuit element, the Nyquist plots of impedance results are fitted with EEC modeling. The bulk resistance obtained from the EEC modeling is used to determine DC conductivity. At room temperature the maximum conductivity of $2.41\times {10}^{-4}\mathrm{S}/\mathrm{c}\mathrm{m}$ is measured. The regions belong to the electrode polarization (EP) effect are distinguished form the spectra of dielectric constant and dielectric loss. Due to the buildup of charge carriers, the dielectric constant and loss are observed to be high at the low-frequency region. Obvious peaks are appeared in the tanδ and M“ spectra at high salt concentrations. Shifting of the tanδ peaks to the high frequency region are detected. The incomplete circular arc of the argand plot is shown the non-Debye relaxation. It is found that with increasing frequency, AC conductivity increased. The regions belong to the EP and DC contributions are differentiated in the AC spectra.