Thermo‐oxidative degradation of HDPE as a function of its crystalline content

The composition, the thermal properties, and the kinetics of the thermo‐oxidative degradation of high‐density polyethylene (HDPE) were studied as a function of the increasing crystalline fraction, which resulted from the selective extraction of the amorphous part, through digestion by immersion in fuming nitric acid (HNO₃) for different periods of time. The chemical and thermodynamic changes in HDPE, brought about by digestion in nitric acid for different periods of time, are discussed. Changes in the chemistry and microstructure of the HDPE, as a function of acid treatment for different periods of time, were studied using infra‐red spectroscopy (FTIR), gel permeation chromatography (GPC), and thermal analysis (DSC and TGA), as well as scanning electron microscopy (SEM). These studies were carried out as a function of the extracted amorphous fraction of HDPE samples via digestion in HNO₃. These studies showed that in the first stages of the acid chemical attack, the amorphous part first undergoes a chemical modification and then dissolves into the strong acid medium. The total crystalline fraction apparently decreases during the first stages of the chemical attack and then increases as the amorphous part is extracted. TGA results show that as the selective extraction of the amorphous part occurs, there is a displacement of the thermo‐oxidative degradation toward higher temperatures. The kinetics of the thermo‐oxidative degradation as a function of the extraction of the amorphous part was followed according to the Horowitz‐Metzger method, and it was found that as the concentration of the crystalline fraction increases, the activation energy for the thermo‐oxidative degradation increases. SEM studies show that the extraction of the amorphous part does not affect the size of the crystalline lamellar thickness of HDPE. © 2009 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 47: 1906–1915, 2009     

PREPARATION OF HIGH DENSITY POLYETHYLENE/POLYETHYLENE-ΒLOCK- POLY(ETHYLENE GLYCOL) COPOLYMER BLEND POROUS MEMBRANES VIA THERMALLY INDUCED PHASE SEPARATION PROCESS AND THEIR PROPERTIES

High density polyethylene (HDPE)/polyethylene-Wock-poly(ethylene glycol) (PE-b-PEG) blend porous membranes were prepared via thermally induced phase separation (TIPS) process using diphenyl ether (DPE) as diluent. The phase diagrams of HDPE/PE-b-PEG/DPE systems were determined by optical microscopy and differential scanning calorimetry (DSC). By varying the content of PE-b-PEG, the effects of PE-b-PEG copolymer on morphology and crystalline structure of membranes were studied by scanning electron microscopy (SEM) and wide angle X-ray diffraction (WAXD). The chemical compositions of whole membranes and surface layers were characterized by elementary analysis, Fourier transform infrared spectroscopy-attenuated total reflection (FTIR-ATR) and X-ray photoelectron spectroscopy (XPS). Water contact angle, static protein adsorption and water flux experiments were used to evaluate the hydrophilicity, antifouling and water permeation properties of the membranes. It was found that the addition of PE-b-PEG increased the pore size of the obtained blend membranes. In the investigated range of PE-b-PEG content, the PEG blocks could not aggregate into obviously separated domains in membrane matrix. More importantly, PE-b-PEG could not only be retained stably in the membrane matrix during membrane formation, but also enrich at the membrane surface layer. Such stability and surface enrichment of PE-b-PEG endowed the blend membranes with improved hydrophilicity, protein absorption resistance and water permeation properties, which would be substantially beneficial to HDPE membranes for water treatment application.     

Thermal,physico‐mechanical,and morphological properties of HDPE graft‐copolymerized with polystyrene

In this study, polystyrene was graft‐copolymerized onto high‐density polyethylene (HDPE) by in situ polymerization of styrene monomer to change the physico‐mechanical and thermal properties of HDPE. The grafting was carried out in a Brabender‐type static mixer by injecting styrene monomer directly into the molten HDPE in the presence of a free‐radical initiator (lauroyl peroxide or LP). The effect of wt% of styrene and initiator concentrations on thermal, physico‐mechanical, and morphological properties of HDPE was investigated. The neat and modified HDPE was characterized by differential scanning calorimetry, thermogravimetric analysis, scanning electron microscopy, Fourier transform infrared spectroscopy, scanning electron microscopy, and also by tensile strength and contact angle measurements. It was found that the increase in wt% of styrene and LP dosage reduced elongation at break, hygroscopic expansion and also the melting, and the crystallization temperatures of HDPE but increased its tensile strength. The tensile strength was increased from 14.6 MPa for the neat HDPE to 20.6 MPA for the 10 wt% of styrene grafted onto HDPE using 0.8% LP. Scanning electron microscopy results show that there was no phase separation, and the grafted polystyrene became integral part of HDPE. The results demonstrate that styrene could be used in melt compounding to improve various properties of HDPE. Copyright © 2015 John Wiley & Sons, Ltd.     

Diffusion Transport in Reconstructed Semi-Crystalline Structure of Polyolefins

Summary: Diffusion of penetrants (e.g., monomers) in polyolefins is important not only in their manufacturing and down-stream processing, but also in packaging and separation applications. We propose a general methodology linking the semi-crystalline structure of polyolefins to their application properties. This methodology comprises of AFM imaging of semi-crystalline structure, reconstruction of 3D replica of semi-crystalline polymer and calculation of application properties (e.g., diffusivity) depending on 3D morphology. Our algorithm is capable to achieve realistic crystallinities of reconstructed samples up to 70% and to reconstruct spherulites with preferential orientation of lamellae. We demonstrate and discuss difficulties experienced during AFM imaging of HDPE morphology, particularly the dependence of resulting AFM image representing the distribution of crystalline domains on the sample preparation including etching.     

Preparation of high density polyethylene/polyethylene-block-poly(ethylene glycol) copolymer blend porous membranes via thermally induced phase separation process and their properties

<正>High density polyethylene(HDPE)/polyethylene-block-poly(ethylene glycol)(PE-b-PEG) blend porous membranes were prepared via thermally induced phase separation(TIPS) process using diphenyl ether(DPE) as diluent.The phase diagrams of HDPE/PE-b-PEG/DPE systems were determined by optical microscopy and differential scanning calorimetry(DSC).By varying the content of PE-b-PEG,the effects of PE-b-PEG copolymer on morphology and crystalline structure of membranes were studied by scanning electron microscopy(SEM) and wide angle X-ray diffraction(WAXD). The chemical compositions of whole membranes and surface layers were characterized by elementary analysis,Fourier transform infrared spectroscopy-attenuated total reflection(FTIR-ATR) and X-ray photoelectron spectroscopy(XPS).Water contact angle,static protein adsorption and water flux experiments were used to evaluate the hydrophilicity,antifouling and water permeation properties of the membranes.It was found that the addition of PE-b-PEG increased the pore size of the obtained blend membranes.In the investigated range of PE-b-PEG content,the PEG blocks could not aggregate into obviously separated domains in membrane matrix.More importantly,PE-b-PEG could not only be retained stably in the membrane matrix during membrane formation,but also enrich at the membrane surface layer.Such stability and surface enrichment of PE-b-PEG endowed the blend membranes with improved hydrophilicity,protein absorption resistance and water permeation properties,which would be substantially beneficial to HDPE membranes for water treatment application.     

Structural and mechanical studies on modified reused tyres composites

Reused tyres powder was used as reinforcement in HDPE-reused tyre composites. In order to improve the compatibility between both components, several pre-treatments performed over the rubber tyres were applied: sulphuric acid etching, use of a silane coupling agent and chlorination with trichloroisocyanuric acid (TCI). Mechanical properties of the resulting materials (e.g. tensile strength, Young’s Modulus, toughness and elongation at break) were studied and compared. Chemical modifications on the surface of reused tyres were monitored by FTIR and physical modifications and behaviour to fracture were followed by means of SEM. The influence of rubber pre-treatment was assessed by comparing the results of treated and untreated composites with those for neat HDPE. Reused tyre rubber, added to the HDPE in small quantities, acts as a filler, improving the stiffness and providing a more brittle behaviour. Pre-treatment with TCI gave poor results in terms of mechanical properties obtaining lower values than neat HDPE in some cases and always worst properties than sulphuric or silane coupling agent. Treatments with H₂SO₄ and silane coupling agent improve the ability of rubber to interact with the HDPE, increasing the material’s stiffness and its tensile strength. Sulphuric acid modificates chemical and physically the particles’ surface improving mainly mechanical adhesion, whereas silane acts as a compatibilizer developing chemical matrix-reinforcement interactions.     

Morphology and mechanical property of high-density polyethylene parts prepared by gas-assisted injection molding

The crystal morphology, melting behavior, and mechanical properties of high-density polyethylene (HDPE) samples obtained via gas-assisted injection molding (GAIM) under different gas pressures were investigated. Moreover, the non-isothermal crystallization kinetics of HDPE under different cooling rates was also studied. The obtained samples were characterized via differential scanning calorimetry, two-dimensional wide-angle X-ray scattering (2D-WAXS), tensile testing, dynamic mechanical analysis (DMA) and scanning electron microscopy techniques. It was found that the properties were intimately related to each other. Macroscopically, the flow-induced morphology of the various HDPE samples was characterized with a hierarchical crystalline structure, possessing oriented lamellar structure, shish?Ckebab structure, and common spherulites in the skin, sub-skin, and gas channel region, respectively. The 2D-WAXS results demonstrated that the degree of orientation of the high gas pressure sample was larger than that of the low pressure sample at the corresponding layer. The tensile testing results of GAIM parts showed that the mechanical properties of the GAIM parts were improved with an increase of the gas pressure. Furthermore, the DMA was utilized to obtain the dynamic mechanical properties of the GAIM samples, and the results indicated that significant improvement of the orientation was observed with an increase of the gas pressure.     

Thermally stimulated dielectric properties of polyvinylidenefluoride–zinc oxide nanocomposites

Thirty-micrometer thick polyvinylidenefluoride (PVDF)–zinc oxide (ZnO) nanocomposite samples in the mass ratio of ZnO (1–6% (w/w)) have been prepared by solution mixing method. The nano- and microstructures of PVDF–ZnO nanocomposite of different mass ratios were characterized by using high-resolution techniques such as atomic force microscopy (AFM) and scanning electron microscopy (SEM). The SEM and AFM images show the presence of different components such as nanoparticles, amorphous and crystalline phases in nanocomposite samples. Dielectric properties of polymer nanocomposite based on PVDF and ZnO of different mass/% compositions have been studied to understand the molecular motion at different frequencies in the temperature range from 300 to 500 K. The permittivity of the nanocomposites decreases with frequency, while increases with the increasing temperature and ZnO content. The loss peak that disappeared at higher frequency is the remarkable result of this study.     

Effects of miscible diluent of poly(ether imide) on ring-banded morphology of poly(trimethylene terephthalate)

The melting, crystallization, and self-packed ring patterns in the spherulites of miscible blends comprising poly(trimethylene terephthalate) (PTT) and poly(ether imide) (PEI) were revealed by optical, scanning electron microscopies (PLM and SEM) and differential scanning calorimetry (DSC). Morphology and melting behavior of the miscible PTT/PEI blends were compared with the neat PTT. Ringed spherulites appeared in the miscible PTT/PEI blends at all crystallization temperatures up to 220 °C, whereas at this high temperature no rings were seen in the neat PTT. A postulation was proposed, and interrelations between rings in spherulites and the multiple lamellae distributions were investigated. The specific interactions and the segregation of amorphous PEI were discussed for interpreting the morphological changes of 220 °C-melt-crystallized PTT/PEI samples. Interlamellar segregation of PEI might be associated with multiple lamellae in the spherulites of PTT/PEI blends; therefore, rings were more easily formed in the PTT/PEI blends at all crystallization temperatures. A postulated model of uneven lamellar growth, coupled with periodical spiraling, more properly describes the possible origin of ring bands from combined effects of both interactions and segregation between the amorphous PEI and PTT in blends.     

Morphology assessment of chemically modified cryostructured poly(vinyl alcohol) hydrogel

The morphology of hydrogels based on poly(vinyl alcohol) (PVA) in their frozen hydrated state, modified with biologically active di- and multifunctional molecules was studied by scanning electron microscopy (SEM) with cryo-attachment. The porosity of samples was found to be more regular and ordered in the case of samples containing difunctional, and especially multifunctional carboxylic acids as compared to the neat PVA hydrogel. The morphology is dependent not only from the hydrogel composition but also the number of freezing-thawing cycles. Resulted highly porous and oriented structure has significant influence on materials properties, such as compressive stress and crosslinking density.     

Glass of the past: The degradation and deterioration of medieval glass artifacts

Medieval artifacts made of glass are at a serious disadvantage concerning the chemical stability compared with ancient or common modern glasses. The total amount of silica and other network formers such as alumina is very low and potassium instead of sodium was introduced into the silicate structure by using local raw material. By means of scanning electron microscopy (SEM), secondary ion mass spectrometry (SIMS) and nuclear reaction analysis (NRA) a weathering mechanism governed by an ion exchange process could be determined for medieval glass paintings exposed to the ambient air for centuries. Additionally, the leached glass surface of medieval hollow glass artifacts found in a well and exposed to moist earth show a brown discoloring due to the oxidation of Mn(II) to Mn(IV) oxide. That process can be converted by a treatment of the glass objects in an aqueous hydrazine solution.     

Effect of MMT,SiO2, CaCO3, and PTFE nanoparticles on the morphology and crystallization of poly(vinylidene fluoride)

The crystallization and melting behaviors of poly (vinylidene fluoride) (PVDF) with small amount of nanoparticles (1 wt %), such as montmorillonite (MMT), SiO₂, CaCO₃, or polytetrafluoroethylene (PTFE), directly prepared by melt‐mixing method were investigated by scanning electron microscopy (SEM), polarizing optical microscopy, Fourier transform infrared spectroscopy, wide angle X‐ray diffraction (WAXD), and differential scanning calorimetry (DSC). The nanoparticle structure and the interactions between PVDF molecule and nanoparticle surface predominated the crystallization behavior and morphology of the PVDF. Small amount addition of these four types of nanoparticles would not affect the original crystalline phase obtained in the neat PVDF sample (α phase), but accelerated the crystallization rate because of the nucleation effect. In these four blend systems, MMT or PTFE nanoparticles could be well applied for PVDF nanocomposite preparation because of stronger interactions between particle surface and PVDF molecules. The nucleation enhancement and the growth rate of the spherulites were decreased in the order SiO₂ > CaCO₃ > PTFE > MMT. The melting and recrystallization of PVDF was found in MMT addition sample, because of the special ways of ordering of the PVDF chains. © 2010 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys, 2010     

New Routes to High Resolution and Automated Polymer Morphology Microscopy via Scanning Electron Microscopy

Summary: Polymer morphologies are traditionally studied by transmission electron microscopy (TEM). With the use of appropriate contrast enhancing heavy metal stains, direct images of the morphology as well as of the lamellar structure of semi-crystalline polymers can be obtained. Despite its clear strengths, this approach faces several challenges and difficulties: the laborious nature of ultra-thin section preparation, high capital investment, and no obvious routes to high-throughput. We propose an alternative approach to cover the major morphology imaging needs based on a new generation of high resolution scanning electron microscopes (SEM) that have been developed in recent years, and that does not rely on the need for ultra-thin section preparation. The proposed approach is capable of not only determining the general phase morphology, but also to image details such as the lamellar structure with sufficient resolution. Our approach is based on the use of backscattered electron imaging at low accelerating voltages. The backscattered electron images show high contrast and information content that is comparable to TEM. The main advantage of our SEM based approach is the ability to examine a polished surface, which requires less demanding sample preparation than producing ultra-thin sections. This opens the door to automated workflows where automated imaging, substantial productivity increases and high speed characterization options can be successfully realized. The successful approach is demonstrated for various polyolefin and engineering plastics samples.     

Preparation of Cu nanoparticles with controlled particle size and distribution via reaction temperature and sonication

This paper presents metallic copper nanoparticles (CuNPs) that differ according to the process parameters used, such as bath temperature and sonication. The effect of different reactions on the size and distribution of CuNPs that had been formed in ethylene glycol solvent were characterized by the X‐ray diffraction (XRD), scanning electron microscopy (SEM), and transmission electron microscopy (TEM) analyses after extraction from the solvent. The optimal dimensional properties, including size, distribution, and agglomeration, of CuNPs were determined by controlling the reaction temperature. On the other hand, the mechanically induced sonication process enhances the formation of the selective CuNPs because of the many homogeneous interactions among precursors, reducing agents, and capping agents related to the nucleation and growth of CuNPs. The mechanics of the origin of the diverse CuNPs of different size and distribution are discussed. Copyright © 2016 John Wiley & Sons, Ltd.     

Effect of Ethylene-Propylene Copolymer Composition on Morphology and Surface Properties of Impact Poly(propylene) Copolymer

Summary: Impact poly(propylene) copolymers (IPC) having various ethylene-propylene rubber (EPR) compositions were prepared using a high activity Ziegler-Natta catalyst. EPR composition was characterized by temperature rising elution fractionation (TREF) analysis and FT-IR spectroscopy. Effect of EPR composition on the morphology and surface properties of IPC was investigated by scanning electron microscopy (SEM), 3D profiler, and gloss meter. Composition and amount of amorphous and crystalline EPR were quantified by TREF and found to be dependent on the ethylene content in EPR. From the SEM result, it was found EPR composition has a strong influence on its shape and size. IPCs containing propylene-rich EPR exhibited a finer dispersion of EPR phase. The surface roughness decreased with decreasing ethylene content in EPR. The comparison of EPR composition and morphology and surface properties exhibited strong correlations.     

Rhythmic growth of ring‐banded spherulites in blends of liquid crystalline methoxy‐poly(aryl ether ketone) and poly(aryl ether ether ketone)

Rhythmic growth of ring‐banded spherulites in blends of liquid crystalline methoxy‐poly(aryl ether ketone) (M‐PAEK) and poly(aryl ether ether ketone) (PEEK) has been investigated by means of differential scanning calorimetry (DSC), polarized light microscopy (PLM), and scanning electron microscopy (SEM) techniques. The measurements reveal that the formation of the rhythmically grown ring‐banded spherulites in the M‐PAEK/PEEK blends is strongly dependent on the blend composition. In the M‐PAEK‐rich blends, upon cooling, an unusual ring‐banded spherulite is formed, which is ascribed to structural discontinuity caused by a rhythmic radial growth. For the 50:50 M‐PAEK/PEEK blend, ring‐banded spherulites and individual PEEK spherulites coexist in the system. In the blends with PEEK as the predominant component, M‐PAEK is rejected into the boundary of PEEK spherulites. The cooling rate and crystallization temperature have great effect on the phase behavior, especially the ring‐banded spherulite formation in the blends. In addition, the effects of M‐PAEK phase transition rate and phase separation rate on banded spherulite formation is discussed. © 2007 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 45: 3011–3024, 2007     

Crystalline morphology of a thermotropic aromatic polyester crystallized from nematic melt

The crystalline morphology of a thermotropic aromatic polyester crystallized from a nematic melt was investigtated by means of polarized optical microscopy (POM) and scanning electron microscopy (SEM). Due to POM measurements it was found that spherulites of two different types are formed within the two different temperature regions. When T_c was exceeding 170°C, spherulites of type‐1 showing a negative birefringence grew with a radial fibrillar morphology and exhibited a clear Maltese‐cross pattern. The radius growth rate of type‐1 spherulites was about 2.2 μm/min at 185°C. When T_c was smaller than 160°C, spherulites of type‐2 were formed and exhibited a radially outward growing structure but no evident Maltese‐cross pattern. These spherulites could be seen by the naked eyes due to their size reaching several millimeters. SEM observations revealed that the spherulites of type‐1 exhibited a ripple‐like homocentric morphology with periodical compact fibrils having a diameter of about 150 nm perpendicular to the radial direction. In contrast, the spherulites of type‐2 exhibited, as apparent from performed SEM images, radially growing crystallites of about 500 nm in size with no periodicity in the radial direction.     

一种水溶性涂料的化学成分分析

采用傅里叶变换红外光谱、电镜/X射线能谱和原子吸收光谱等现代仪器测试方法对一种水溶性涂料的化学成分进行检测分析,对材料的红外光谱特征进行解析,综合定性和定量分析结果,确定出该涂料的各种组份及其配比.     

Reactively compatibilized and dynamically vulcanized thermoplastic elastomers based on high-density polyethylene and reclaimed rubber

Melt blending was employed to prepare thermoplastic elastomer (TPE) of reclaimed rubber (RR) and high density polyethylene (HDPE). Mechanical properties of TPE samples were improved in different methods including dynamic vulcanization and reactive blending (reactive compatibilization) during melt mixing in an internal Haake mixer. The physical and mechanical properties of the TPE blends were investigated by the dynamic mechanical analysis (DMA) and tensile tests. The thermal behavior was characterized by differential scanning calorimeter (DSC) and thermogravimetric analysis (TGA). The phase morphology of the blends was studied by scanning electron microscopy (SEM). Experimental results showed that, both static and dynamic mechanical properties of reactively-compatibilized and dynamically-vulcanized samples improved significantly compared with the virgin samples. The effect of dynamic-vulcanization and reactivecompatibilization on the mechanical properties revealed that the Young’s modulus and storage modulus increased with both improvement methods. SEM results showed that, dynamic-vulcanization and reactivecompatibilization methods improved the distribution of RR particles in HDPE matrix. Although both methods improved the thermal and mechanical properties of the HDPE/RR blends, dynamic-vulcanization was more effective and promising approach due to the higher properties of HDPE/RR blends prepared by this method.     

一个低分子量聚氧化乙烯从亚稳态的折叠链片晶向稳态的伸直链片晶转化增厚过程的研究

报道分子量为5000的聚氧化乙烯(PEO)从熔融态淬火到液氮温度后形成的两次链折叠(2-FC)片晶增厚过程的研究结果.在升温和恒温条件下,采用小角X射线散射(SAXS)在位地跟踪了2-FC片晶增厚成一次链折叠(1-FC)和进一步成为伸直链(EC)片晶的增厚过程.通过对SAXS数据以及它们的一维相关函数的数据的分析,发现在52℃以下,2-FC片晶主要增厚为1-FC片晶;在52℃以上,2-FC片晶则主要增厚为EC片晶;在58℃到EC片晶的熔点的温度区域里,已经形成的1-FC片晶还会熔融,完全转化为EC片晶.利用偏光显微镜(PLM)和扫描电子显微镜(SEM)观察晶体的形貌,比如球晶,获得的研究结果表明,没有发生大范围的晶体破坏后再形成的变化,也就是说片晶的增厚过程是一个发生在球晶内部的薄片晶熔融后转化为厚片晶的过程.