Structural depth profiling in polyethylene films by multiple internal reflection infra-red spectroscopy

The technique of internal reflection spectroscopy is used for the study of the structural gradient from the outer skin into the core in a commercial polyethylene film. A method is proposed for the quantitative evaluation of the relative amount of amorphous versus crystalline material. It is shown that the skin is highly crystalline and that an approximate amount of 40% amorphous material is found in the core of the film. The method used is of general validity for any polymer once bands characteristic of the amorphous and crystalline or regular structures are identified.     

Use of photoacoustic spectroscopy in studying the natural weathering of polyethylene films

Photoacoustic spectroscopy was used to assess the degradation of polyethylene under local natural weathering conditions. The results obtained are in good agreement with those obtained using infrared spectroscopy and from mechanical testing. Photoacoustic spectroscopy supports the accepted mechanism of polyethylene degradation.     

Low-density polyethylene filled with chalk and liquid modifier

Based on the concept of introducing a liquid layer between the polymer and filler, a composition containing low-density polyethylene, chalk, and oligomer of ethylene oxide was proposed. Compositions containing up to 50% chalk modified with ethylene oxide exhibit typical thermoplastic behavior, i.e., neck formation and plastic deformation. They also show high-impact strength and other good properties. On the basis of mechanical data, the main action of the ethylene oxide oligomer in the system is to inhibit crack generation and propagation.     

Mechanical degradation of PVC films monitored by photoacoustic spectroscopy

PVC films were subjected to mechanical degradation at room and elevated temperatures and monitored by photoacoustic spectroscopy. Broken bonds in the main PVC chain result in the formation of “mechano-radicals,” which in turn yield a zipper reaction and the formation of submicrocracks in the PVC samples. The mechanistic schemes based on the formation of the mechano-radicals are introduced and are successfully supported by the experimental results.     

Low-density polyethylene/polyamide 6 blends from multilayer films waste

Multilayer films combine properties of different polymers in a single material, attending specifications to applications such as packaging. However, the mechanical recycling for this material king is commercially less interesting because the polymeric components cannot easily be separated and the direct mechanical processing of the material leads to the immiscible and incompatible polymeric blends. The aim of this study was to evaluate properties of the blends of low-density polyethylene (LDPE) and polyamide 6 (PA6) generated from mechanical recycling of multilayer films constituted by LDPE and PA6, containing maleic anhydride grafted polyethylene (PE-g-MA) as compatibilizing agent and different amounts of virgin PA6. The LDPE/PA6 blends are immiscible for all composition and the use of PE-g-MA has showed little effect on the compatibility of the blends with high content of PA6. However, LDPE/PA6 blends with PA6 content up to 20 wt % showed considerable performance for mechanical performance that can justify the mechanical recycling of the material. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 136, 47456     

Phase diagrams of polyethylene blends by Raman spectroscopy

Summary The Raman internal mode region analysis of polyethylene (PE) is extended to studies of blends of different PEs so as to obtain a phase diagram showing the magnitude of crystalline (P_c), amorphous (P_a) and interfacial (P_b) phases at different compositions. The non-cocrystallizable HDPE/LDPE blends shows additivity in phase structure with blend composition. Enlarged share of P_b is seen for compatible blends of HDPE/LLDPE and especially for HDPE with VLDPE of low crystallinity. This method offers an easy access to direct observing compatibility of different PEs on a molecular level. Supported by Chinese Petrochemical Corporation (SINOPEC)     

Low-density polyethylene modified by thermal polymerization of 4-vinylpyridine and methyl methacrylate: Structural studies

The structures of low-density polyethylene (LDPE) modified by in situ sorption and thermal polymerization of 4-vinylpyridine (4VP) and of methyl methacrylate (MMA) were studied. The phase behavior of these materials was investigated by means of X-ray diffraction, scanning electron microscopy (SEM), and by thermal measurements (DSC). The diffraction studies indicated that the polymerization occurs at the amorphous domains of the matrix, except for the case of 4VP (168.0%), in which polymerization at the crystalline domains of LDPE matrix was also observed. These materials showed at least two T_g values, indicating microphase separation. The morphology of LDPE-P4VP was different from that of LDPE-PMMA.     

Fourier transform infrared photoacoustic spectroscopy of raw coal

Photoacoustic Fourier transform infrared (PA-FT-i.r.) spectrometry was employed to examine raw coal containing 13–64 wt%, daf volatile matter (VM). Sample preparation for i.r. examination was the same as for ASTM proximate analysis. Technological and spectroscopic information on representative samples were obtained. PA scan time is longer than for conventional FT-i.r. operation; however sample preparation is faster and easier. The time-consuming KBr pellet technique, possibly affecting coal structure, is avoided. The i.r. absorption in the OH, NH, CH_ar and CH_x,al regions may allow the determination of VM for both high- and low-rank coal. Some differences between present PA and diffuse reflectance spectra of raw coal from the literature are discussed.     

Glass transition of polyethylene as studied by Brillouin spectroscopy

Summary The Brillouin spectrum of polyethylene has been measured as a function of temperature. Slope discontinuities of opposite directions have been observed in the Brillouin shift and width near the glass transition temperature. The former is attributed to a corresponding discontinuity in the temperature coefficient of specific volume, while the latter to the onset of long-range coordinated molecular motion near the transition region.     

Crystalline melting of polyethylene as studied by Brillouin spectroscopy

Summary The Brillouin spectrum of polyethylene has been measured as a function of temperature through the crystalline melting range, using a five-pass Fabry-Perot interferometer. Discontinuities have been observed in the Brillouin shift and width and the Landau-Placzek ratio near the melting temperature. The results are discussed in terms of phenomena associated with the process of melting.     

Characterization of semisolid fats and edible oils by Fourier transform infrared photoacoustic spectroscopy

The potential of Fourier transform infrared photoacoustic spectroscopy (FTIR-PAS) for the analysis of semisolid fat and edible oil was demonstrated with butter, soybean oil, and lard as representative materials. Results of Fourier transform infrared attenuated total reflectance (FTIR-ATR) spectroscopy analysis was compared with FTIR-PAS results. The PAS technique is simple and requires no sample preparation unlike ATR. Optimal PAS instrumental parameters for obtaining quality spectra are a scanning speed of 5 kHz, number of scans of 256 scans/sample, and a resolution of 4 cm⁻¹. The PAS spectra of soybean oil and lard are similar because they have similar functional groups. Results for soybean oil compare well with those available in the literature. The ATR spectra of butter were better than those from its PAS counterpart. Functional groups corresponding to vibration mode and intensity are provided for soybean oil and lard.     

Photo- and thermal-oxidation of the nonwoven polypropylene fabric studied by FT-IR photoacoustic spectroscopy

The photo- and thermal-oxidation of a nonwoven polypropylene fabric was investigated using Fourier transform infrared photoacoustic spectroscopy (FT-IR/PAS). The infrared spectroscopic data indicate that alcohol, peroxide, aldehyde, ketone, carboxylic acid, and anhydride were formed as the products of the thermal oxidation and photooxidation of the polypropylene fabric. Ester was also formed during the thermal oxidation process. The thermal oxidation was accelerated after an initiation period. It was found that thermal oxidation occurred homogeneously between the surfaces of the fabric and its bulk. For the polypropylene fabric irradiated by ultraviolet (UV) radiation, however, the highest degree of oxidation occurred in the surface of the fabric facing the UV radiation source. It was also found that the UV radiation at 254 nm caused photooxidation of polyropylene. No photooxidation was observed in the fabric exposed to the UV radiation at 350 nm under the same conditions. © 1994 John Wiley & Sons, Inc.     

Infrared photoacoustic and dynamic mechanical spectroscopy of sheet-molded compounds

Chemical and physical characteristics of sheet-molded compounds were investigated using infrared and mechanical spectroscopies. Fourier transform infrared spectroscopy with photoacoustic detection facilitated surface analysis for determination of composition, depth profile, and thermal exposure effects. Dynamic mechanical spectroscopy utilized torsion, tension, and flexure modes to evaluate temperature and frequency-dependent viscoelastic properties.     

Conductivity model and photoacoustic FT-IR surface depth profiling of heterogeneous polymers

A novel thermal model is developed for surface depth profiling of heterogeneous polymeric surfaces using step-scan photoacoustic Fourier transform (SS PA FT-IR) spectroscopy. This approach is based on the propagation of thermal waves generated during the photoacoustic effect which travel to the film-air (F-A) interface, thus generating acoustic signals above the surface, which upon Fourier transform, result in infrared spectra. The developed model volumetrically slices the surface into finite homogeneous layers parallel to the film-air (F-A) interface and a composition of each ith layer is assumed to be the same, but the layers among themselves (ith+1 and ith−1) may or may not exhibit compositional changes. Overall thermal properties of the multi-layered surface consist of the sum of in-series connected thermal conductor layers. The proposed model can be utilized to polymeric films containing the following parametrically analyzed inclusions: (1) inclusions with no interphase between the matrix polymeric and (2) inclusions with a finite interphase. This model is flexible, allowing variations of the particle size, shape, and surface/interfacial microstructural changes. It was tested for depths of penetrations in the range of 5-50 μm for carbon black inclusions imbedded into a two-component (2K) polyurethane (PUR) film deposited on acrylonitrile-butadiene-styrene (ABS) substrate. These studies show that the experimental results are consistent with the proposed model, allowing predictions of interphase layers on particles; for example, a 10 nm water layer adsorbed on carbon black particle surfaces can be detected.     

Poly(lactic acid)/polystyrene bioblends characterized by thermogravimetric analysis,differential scanning calorimetry,and photoacoustic infrared spectroscopy

Bioblends are composites of at least one biodegradable polymer with nonbiodegradable polymer. Successful development of bioblends requires that the biodegradable polymers be compatible with other component polymers. Compatibility can be assessed by evaluating the intermolecular interactions between the component polymers. In this work, the interaction in binary bioblends comprising biodegradable poly(lactic acid) (PLA) and polystyrene (PS) was investigated using thermogravimetric analysis (TGA), differential scanning calorimetry (DSC), and Fourier transform infrared photoacoustic spectroscopy (FTIR‐PAS). The TGA studies indicated that incorporation of PLA in PS resulted in thermal destabilization of PS. The DSC studies showed that some parameters favored partial miscibility of PS in PLA, while others favored immiscibility, such as the existence of two glass transitions. The FTIR‐PAS spectra revealed the presence of intermolecular n–π interactions between PLA and PS and indicated that the degree of interaction was dependent on the concentrations of the polymers in the bioblends. FTIR‐PAS results computed via differential spectral deconvolution were consistent with, and therefore support, the results of TGA and DSC analyses of PLA/PS bioblends. The degradation kinetics, used to determine the degradation mechanism, revealed a two‐ or three‐step mechanism. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2007     

Some orientation studies on blown polyethylene films by infrared spectroscopy

Infrared dichroic measurements have been made on a number of blown polyethylene films for which x-ray diffraction pole figure studies are reported in the three preceding papers; they complement them in some respects, and lead to several conclusions. Gauche chain conformations in loose chain folds in amorphous regions, characterized by bands at 1303, 1352, and 1368 cm^-1, show appreciable orientation in films with high-stress orientation but very little with low-stress orientation. Conversely, extended tie chains in amorphous regions, assessed by the band at 1080 cm^-1, are appreciably orientated with the more normal type of low-stress film but not with high-stress films. It is therefore possible, rapidly and inexpensively, to distinguish between the two types of orientation. The method for studying the orientation of extended tie chains is capable of further development. There is probably an empirical correlation between the dichroic ratios at 720 and 730 cm^-1 and the tear strengths and balances of the films with low-stress orientation.