Thermal and wide angle X‐ray analysis of chemically and radiation‐crosslinked low and high density polyethylenes

Low and high density polyethylenes (PE) were crosslinked by two methods, namely, chemically by use of different amounts of tert‐butyl cumyl peroxide (BCUP) and by irradiation with different doses of electron beam. A comparison between the effects of these two types of crosslinking on crystalline structure, crystallinity, crystallization, and melting behaviors of PE was made by wide angle X‐ray diffraction and DSC techniques. Analysis of the DSC first heating cycle revealed that the chemically induced crosslinking, which took place at melt state, hindered the crystallization process and decreased the degree of crystallinity, as well as the size of crystals. Although the radiation‐induced crosslinking, which took place at solid state, had no significant influence on crystalline region, rather, it only increased the melting temperature to some extent. However, during DSC cooling cycle, the crystallization temperature showed a prominent decrease with increasing irradiation dose. The wide angle X‐ray scattering analysis supported these findings. The crystallinity and crystallite size of chemically crosslinked PE decreased with increasing peroxide content, whereas the irradiation‐crosslinked PE did not show any change in these parameters. As compared with HDPE, LDPE was more prone to crosslinking (more gel content) owing to the presence of tertiary carbon atoms and branching as well as owing to its being more amorphous in nature. HDPE, with its higher crystalline content, showed relatively less tendency toward crosslinking especially by way of irradiation at solid state. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 100: 3264–3271, 2006     

Physicomechanical,optical, barrier,and WAXS studies of filled linear low‐density polyethylene films

Linear low‐density polyethylene (LLDPE) with different fillers such as silica, mica, and soy protein isolate were compounded using a single screw extruder and blown into films by a Konark blow‐film machine. The filled LLDPE films were characterized for physicomechanical and optical properties. Barrier properties such as water vapor transmission rate and oxygen transmission rate of the filled LLDPE films were also reported. Microcrystalline parameters such as crystal size (〈N〉) and lattice distortion (g in %) of the filled LLDPE films were estimated from the wide‐angle X‐ray scattering method using Hosemann's paracrystalline model. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 90: 2938–2944, 2003     

Small‐angle X‐ray scattering investigation of the deformation processes in the amorphous phase of high density polyethylene

In situ small‐angle X‐ray scattering of high density polyethylene under uni‐axial tensile test was used for investigating the deformation at the scale of the periodic crystalline–amorphous nano‐structure. The more or less uniform elastic straining of the rubbery amorphous layers is discussed in terms of mechanically active intercrystalline tie chains. Correlation is made with the long‐term use properties. It is concluded that this approach is a powerful means to assess the mechanical efficiency of tie molecules. Copyright © 2004 Society of Chemical Industry     

Recent developments in polymer applications of synchrotron small‐angle X‐ray scattering

Synchrotron radiation facilities have been established and become very familiar in the polymer community not only from academic but also industrial viewpoints. It is not so unusual now to conduct simultaneous measurements of small‐angle X‐ray scattering (SAXS) with other techniques such as wide‐angle X‐ray scattering, stress–strain, light scattering, and so forth. New techniques have also been established and have become more familiar in recent years. In this review, recent developments in polymer applications of synchrotron SAXS are summarized. Instrumental developments and progress in data analyses are reviewed from the following aspects: ultra‐small‐angle X‐ray scattering, anomalous SAXS, X‐ray photon correlation spectroscopy, new types of simultaneous measurements, grazing‐incidence SAXS, new trends in nanoparticle analyses and industrial applications. © 2016 Society of Chemical Industry     

Microstructural investigation of butt‐fusion joint in high‐density polyethylene pipes using wide‐ and small‐angle X‐ray scattering

The melt fusion zone (MFZ) of polyethylene pipe was investigated employing synchrotron wide‐ and small‐angle X‐ray scattering at various locations in MFZ by changing X‐ray incidence angles to probe three‐dimensional structural features. It was determined that the crystals were oriented in two different modes. One is that the polymer chains are oriented parallel to the joint interface line consistently throughout the MFZ. The other is that the crystals are oriented in particular directions depending on the positions in MFZ. The combination of pressure and melt flow during joining process resulted in such a complex structure. It was notable that the boundary of MFZ against the base material was found to be very different depending on the structures involved such as crystallographic unit orientation, lamellae orientation, crystallinity, and spherulitic morphology. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018 , 135, 45668.     

X‐ray diffraction characterization of the structure of zein–Oleic acid films

Wide‐angle (WAXS) and small‐angle X‐ray scattering (SAXS) studies of dry granular zein, zein fibers, zein–oleic acid resin, and zein–oleic acid films are reported. WAXS patterns showed two diffuse rings for these samples indicative of noncrystalline structures. Measured d‐spacings of ∼ 4.6 Å and ∼ 10.5 Å were found for zein–oleic acid resins and films, consistent with the presence of α‐helical segments. The granular zein and zein fibers had ∼ 4.6‐Å and ∼ 9.5‐Å spacings. Neither the films nor the fibers showed evidence of orientation of the molecular axes. SAXS studies of zein–oleic acid films indicated that the structure of the films was affected by preparation method. Biaxially drawn resin films showed periodicities of ∼ 170 Å along the film surface direction and ∼ 135 Å in the thickness direction, while the cast films had weaker intensity periodicities of ca. 80 Å for all beam directions; a weak, diffuse 45‐Å spacing was also observed for both samples. The 170‐Å periodicity was present in the resin before deformation and following uniaxial deformation. No SAXS periodicity was observed for the granular zein or zein fibers. Several structural models are presented for the resin films that are consistent with reports in the literature that zein, in solution, consist of prism‐like particles consisting of four or more molecules. ? 1999 John Wiley & Sons, Inc. J Appl Polym Sci 71: 1267‐1281, 1999     

About the Lorentz correction used in interpretation of small‐angle X‐ray scattering data of semicrystalline polymers

Lorentz correction is used to correct the intensities of X‐ray scattering of single‐crystal diffractometry in order to recalculate intensities to obtain structure factors. This correction reduces the intensities to zero at zero diffraction angle. Small‐angle scattering is used to study the dimensions of heterogeneities in polymeric materials. The scattering intensities at a near to zero scattering angle originate partly from periodic systems (reciprocal lattice) and partly from dispersed particle systems. Periodic systems should result in individual Gaussian or Lorentzian peaks with the position of a peak maximum depending on the length of the periodicity. Particle scattering results in a Gaussian peak centered at zero scattering angle. The effect of the Lorentz correction on the interpretation of small‐angle X‐ray scattering data is shown for some semicrystalline polyethylenes (high‐density, linear low‐density, and low‐molecular‐weight waxy polyethylenes). The data are compared to those for amorphous block copolymers (styrene–butadiene), in which there is a periodic system with homogeneous lamellar thickness. Lorentz correction destroys the characteristics of the particle scattering and can be applied only for periodic systems. It should not be used to produce a peak on scattering data, which do not show periodicity (peaks) without correction. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 80: 358–366, 2001     

Electrical,physicomechanical, and X‐ray studies on ethylene‐vinyl acetate copolymer/polyaniline blends

The conductive blend consisting of ethylene‐vinyl acetate (EVA) and a polyaniline/p‐toluene sulfonic acid (PAn/TSA) complex were prepared by a thermal doping process using a Brabender plasticorder at 150°C. The conductivity, dielectric constant, dissipation factor, mechanical behavior, and structural aspects of these blends were investigated. A higher percentage of the PAn/TSA complex in the EVA matrix resulted in an increase in the electrical properties and a decrease in the mechanical properties like the tensile strength and percentage of elongation. These results were compared with the microcrystalline parameters of the blend obtained from X‐ray profile analysis. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 83: 1730–1735, 2002     

About the Lorentz correction used in the interpretation of small angle X‐ray scattering data of semicrystalline polymers

Lorentz correction is used to correct the intensities of X‐ray scattering of single crystal diffractometry in order to recalculate intensities to obtain structure factors. This correction reduces the intensities to zero at zero diffraction angle. Small angle scattering is used to study the dimensions of heterogeneities in polymeric materials. The scattering intensities near to zero scattering angle originate partly from periodic systems (reciprocal lattice) and partly from dispersed particle systems. Periodic systems should result in individual Gaussian or Lorentzian peaks with the position of a peak maximum depending on the length of the periodicity. Particle scattering results in a Gaussian peak centred at zero scattering angle. The effect of the Lorentz correction on the interpretation of small angle X‐ray scattering data is shown in the case of some semicrystalline polyethylenes (high density, linear low density, and low molecular weight waxy polyethylenes). The data are compared with those for amorphous block copolymers (styrene/butadiene) in which there is a periodic system with homogeneous lamellar thickness. Lorentz correction destroys the characteristics of the particle scattering and can be applied only for periodic systems. It should not be used to produce a peak on scattering data which does not show periodicity (peaks) without correction. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 80: 2300–2308, 2001     

Microfocus small‐angle X‐ray scattering investigation of the skin–core microstructure of lyocell cellulose fibers

Skin–core microstructures in hydrated lyocell cellulose fibers were investigated using microfocus small‐angle X‐ray scattering (SAXS). Both single fibers and fiber cross sections were observed. In all the fibers studied, a thin skin layer was observed in which the voids were smaller in cross section and better oriented than those in the core. The division between skin and core may not be sharp. A draw ratio of 0.80 gave fibers with voids that were shorter, larger in cross section, and more misoriented than the fibers produced with a draw ratio of 1.68. In contrast, there was little difference in void structure between samples coagulated in water and in 25% amine oxide aqueous solution. The results are explained in the context of the spinodal decomposition, which is thought to occur during coagulation. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 83: 2799–2816, 2002; DOI 10.1002/app.10256     

Development of environmentally friendly high‐density polyethylene and turmeric spent composites: Physicomechanical,thermal, and morphological studies

High‐density polyethylene (HDPE)/turmeric spent (TS) composites were prepared by the extrusion of an HDPE resin with 5, 10, 15, or 20 wt % TS. HDPE granules and TS master‐batch flakes were compounded on a corotating and intermeshing twin‐screw extruder. The extrudate strands were cut into pellets and injection‐molded to make test specimens. These specimens were tested for physicomechanical properties such as the tensile, flexural, and impact strengths, surface hardness, abrasion resistance, density, and water absorption and thermal characteristics such as the heat distortion temperature (HDT) and melt flow index (MFI). Test results revealed that the incorporation of TS affected the tensile, flexural, and Izod impact strengths of the HDPE/TS composites to some extent, whereas the tensile modulus increased from 606.9 to 752.0 N/mm² and the HDT increased from 61 to 65°C. Furthermore, the addition of TS yielded only marginal variations in the surface hardness, abrasion resistance, density, water absorption, and MFI values of the composites. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

X‐ray diffraction studies on reverse‐annealed polyethylenes

Linear low and high density polyethylene sheets were compression molded and crystallized at a 5–10°C/min cooling rate. Parts of the sheets were annealed at different temperatures up to 2°C below the melting temperature. The small angle X‐ray scattering (SAXS) and the wide angle X‐ray scattering intensities of the annealed samples were studied. SAXS intensities showed particle scattering with a bimodal size distribution. The estimated radii of gyration were 15–17 nm and 5–7 nm, respectively. The crystallinity and the radius of gyration increased slightly with increasing annealing temperature for some samples; others did not show any change. No peaks characteristic of intercorrelated lamellar crystallinity in the SAXS intensities developed during the annealing. The original broad peak of high density polyethylene disappeared from the SAXS recordings on annealing. The length of the perfect chain versus melting temperature was calculated by the Thomson‐Gibbs formula and Flory's concept of melting temperature depression where methyl groups and tertiary carbon atoms at the branches were regarded as second components (solvent). Linear relationships were found for both cases. Experimental data for a linear low density polyethylene obtained from the literature were in between the two functions. A lamellar model of crystallization corresponding to the data is proposed. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 81: 340–349, 2001     

A study of the morphology of polyurethane–polystyrene interpenetrating polymer networks by means of small angle X‐ray scattering,modulated‐temperature differential scanning calorimetry,and dynamic mechanical thermal analysis techniques

The morphology of polyurethane–polystyrene (PU‐PS) (60 : 40 by weight) interpenetrating polymer networks (IPNs), in which internetwork grafting via 2‐hydroxyethyl methacrylate resides (HEMA) (1, 2.5, and 10 wt %, respectively) in the polystyrene networks has been studied by means of small angle X‐ray scattering (SAXS), modulated‐temperature scanning calorimetry (M‐TDSC), and dynamical mechanical thermal analysis (DMTA) techniques. With increasing internetwork grafting, the average size of domains became smaller (SAXS data) and the degree of component mixing increased (M‐TDSC and DMTA results). For the PU‐PS (60 : 40 by weight) IPN with 10% HEMA, the DMTA tan δ‐temperature plot showed a single peak. This DMTA result implied that the morphology of this PU‐PS IPN is homogeneous. However, the M‐TDSC data showed that three PU‐PS (60 : 40) IPNs samples (with 1, 2.5, and 10 wt % HEMA, respectively) were phase separated. For the three IPN samples, the correlation length of the segregated phases, obtained from SAXS data based on the Debye–Bueche method, did not show distinct differences. With increasing internetwork grafting, the scattered intensity decreased. This study concluded that for these IPNs, SAXS is sensitive to the size of domains and component mixing, but no quantitative analysis was given for the component mixing. M‐TDSC is suitable to be used to quantify the degree of component mixing or the weight fraction of interphases, and DMTA is sensitive to damping behavior and to phase continuity. However, DMTA cannot provide quantitative information about the degree of component mixing or the weight (or volume) fraction of the interphases. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 79: 1958–1964, 2001     

On the fractal character of polymer spherulites: an ultra‐small‐angle X‐ray scattering study of poly[(R)‐3‐hydroxybutyrate]

Ultra‐small‐angle X‐ray scattering (USAXS) and small‐angle X‐ray scattering (SAXS) measurements are presented for poly[(R)‐3‐hydroxybutyrate] (PHB) crystallized at room temperature. The USAXS patterns indicated that the spherulites had a radially orientated fibrillar nanostructure with fractal geometry over a length scale ranging from 12 nm up to at least 300 nm, with a mass fractal dimension of approximately 2.7 in aged samples. The SAXS patterns indicated that the fibrils themselves were built up of bundles of crystalline lamellae separated by layers of disordered material, with a period length of approximately 6 nm. The SAXS measurements during primary crystallization gave an initial fractal dimension of 4 during spherulite growth, due to the sharp phase boundary between the spherulites and the melt. Copyright © 2004 Society of Chemical Industry     

In situ small angle X‐ray scattering study on structural evolution of crosslinked polytetrafluoroethylene during deformation

The structural evolution of virgin and crosslinked polytetrafluoroethylene (PTFE) during stretching was studied by in situ synchrotron small‐angle X‐ray scattering (SAXS). Both yield and tensile stress of crosslinked PTFE increased with increasing crosslinking density. During stretching, for virgin PTFE, amorphous chains gradually turned to tensile direction at early stage, perpendicularly arranged lamellar stacks appeared at high strains (>140%). While for crosslinked PTFE, lamellar structure was observed even at lower strains; with increasing irradiation dose, the lamellar structure became obvious and the long period decreased. Four‐point SAXS patterns were observed only in 3000kGy‐dosed PTFE during deformation, which indicated that an alternately tilted lamella arrangement called herringbone structure was formed. Radiation dose induces crosslinked networks formed, which can carry part of local stress during deformation, resulting in the increase of yield and tensile stress. Crosslinking density is an important factor on structural evolution. In addition, a deformation mechanism of different crosslinked PTFE is proposed. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 39883.     

Reduction in tactoid size as a means for reinforcing high‐density polyethylene/montmorillonite nanocomposites

Nanocomposites were prepared by adding montmorillonite clay to a high‐density polyethylene matrix. Their structure, morphology, thermal behavior, and physical– mechanical properties were studied. The filler did not alter much the structure and morphology of the matrix, with the exception of a disruptive effect on the lamellar stacks. The crystallization behavior, equilibrium melting temperature, and work of chain folding of the nanocomposites were also unaltered with respect to that of the PE base polymer. However, significant improvements in physical–mechanical properties were observed. The reason for this increase in performance was ascribed to the interaction between the filler and the matrix, especially because of a reduction in size of the original tactoids to stacks of just a few layers, albeit not intercalated. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Rice bran‐filled biodegradable low‐density polyethylene films: Development and characterization for packaging applications

Rice bran was incorporated into low‐density polyethylene (LDPE) at different concentrations by compounding in a twin‐screw extruder and blown into films of uniform thickness. The rice bran incorporation influenced physical, mechanical, barrier, optical, thermal properties, and biodegradation of LDPE. The mechanical and optical properties decreased as the percentage of rice bran increased. The effect of rice bran on the morphology of LDPE blends was examined using scanning electron microscopy. Oxygen transmission rate and water vapor transmission rate increased with the increased content of rice bran. Addition of rice bran did not alter the melting temperature (T_m) of the blends; however the thermal stability decreased, while glass transition temperature (T_g) increased. Kinetics of thermal degradation was also investigated and the activation energy for thermal degradation indicated that for up to 10% filler addition, the dispersion and interfacial adhesion of rice bran particles in LDPE was good. Aerobic biodegradation tests using municipal sewage sludge and biodegradation studies using specific microorganism (Streptomyces species) revealed that the films are biodegradable. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 102: 4514–4522, 2006     

Time‐resolved small‐angle X‐ray scattering study of void fraction evolution in high‐density polyethylene during stress unloading and strain recovery

By means of time‐resolved small‐angle X‐ray scattering, we developed an analysis methodology to assess the void volume fraction ?_v in high‐density polyethylene (HDPE) during tensile testing. The specimens were first drawn up to different imposed strains, and subsequently were subjected to stress unloading and strain recovery stages. During the loading stage, ?_v progressively increased with the strain level, starting from a well‐defined onset strain prior to the yield point. In particular, ?_v reached a maximum of 8.75 vol% for a strain of 12.5% in the case of a HDPE grade with a molecular weight of 105 000 g mol^?1. Stress unloading and strain recovery caused a decrease in ?_v attained at the end of the loading stage. For a HDPE grade with a molecular weight of 55 000 g mol^?1, ?_v was more important during the loading stage and the decrease in ?_v was less marked during the stress unloading stage when compared to the HDPE with molecular weight of 105 000 g mol^?1. The residual and reversible components of void volume fraction were revealed. © 2015 Society of Chemical Industry     

Blend of high‐density polyethylene and a linear low‐density polyethylene with compositional‐invariant mechanical properties

This article presents the tensile properties and morphological characteristics of binary blends of the high‐density polyethylene (HDPE) and a linear low‐density polyethylene (LLDPE). Two constituents were melt blended in a single‐screw extruder. Injection‐molded specimens were evaluated for their mechanical properties by employing a Universal tensile tester and the morphological characteristics evaluated by using a differential scanning calorimeter and X‐ray diffractometer. It is interesting to observe that the mechanical properties remained invariant in the 10–90% LLDPE content. More specifically, the yield and breaking stresses of these blends are around 80% of the corresponding values of HDPE. The yield elongation and elongation‐at‐break are around 65% to corresponding values of HDPE and the modulus is 50% away. Furthermore, the melting endotherms and the crystallization exotherms of these blends are singlet in nature. They cluster around the corresponding thermal traces of HDPE. This singlet characteristic in thermal traces entails cocrystallization between these two constituting components. The clustering of thermal traces of blends near HDPE meant HDPE‐type of crystallites were formed. Being nearly similar crystallites of blends to that of HDPE indicates nearness in mechanical properties are observed. The X‐ray diffraction data also corroborate these observations. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 83: 2604–2608, 2002     

Sago starch‐filled linear low‐density polyethylene (LLDPE) films: Their mechanical properties and water absorption

Composites containing various percentages of sago starch and linear low‐density polyethylene (LLDPE) have been prepared. The mechanical properties and water uptake of the composites have been determined. The tensile strength and elongation at break decreased with increase in starch content. However, the modulus of the composites increased with increase in starch content. The yield strength was not significantly affected. Moisture uptake in humid air and in water increased with increase in starch content. At higher relative humidity the composites absorbed more moisture, thus indicating that the moisture barrier properties decreased with increase in relative humidity. Moisture uptake was highest when the composites were completely immersed in water. Scanning electron microscopy (SEM) shows agglomeration of the starch granules and hence, poor wetting between the starch granules and LLDPE matrix. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 79: 29–37, 2001