Random Copolymer Of Ethylene Research Articles

Very long-time crystallization kinetics for ethylene-methacrylic acid ionomers neutralized with zinc, sodium, lithium and magnesium

Papers by our group [1] (Grady et al., 2013) and another group [2] (Paul et al. 2012) examined crystallization of random copolymers of ethylene and methacrylic acid after room temperature annealing. Similar conclusions were reached concerning the crystallization process; primary crystals were either unchanged or changed very little after annealing while secondary crystallization occurred over long time scales after annealing. The current work confirms these general conclusions for four different cations (Zn2+, Na+, Li+ and Mg2+), with the latter two not studied in either of the previous studies. Even after 6 years of annealing at room temperature, the crystallization rate is constant with logarithmic time, i.e. the material continues to crystallize. The acid copolymer does not crystallize with room temperature annealing, although secondary crystals of the acid copolymer thicken with annealing.

Melt memory in random ethylene-1-alkene copolymers.

Chain flexibility or stiffness based polymer conformation plays a crucial role in affecting the dynamics and kinetics of polymers, which is related to the hierarchical architecture of chains. A series of random copolymers of ethylene and 1-alkenes including 1-hexene, 1-octene, and 1-dodecene were synthesized with metallocene catalysts. The crystallization behavior and memory effect in random ethylene-1-alkene copolymers with different side groups were investigated via differential scanning calorimetry (DSC) and wide-angle X-ray scattering (WAXS). Rheological tests were performed for understanding their dynamical behavior. The results show that the melting peak and the viscosity decrease but the orthorhombic crystal dimensions increase with co-unit contents increasing in the copolymers. It was found that the scaling relationship between the zero shear viscosity (η0) and molecular weight (Mn) of the copolymers containing ethylene-1-hexene and ethylene-1-octene is 3.6, which is higher than the classical scaling value of 3.4. The memory of crystals in the melt is enhanced with the increase of 1-alkene contents but is independent of the types of 1-alkenes. The enhanced melt memory effect in the copolymers was proposed due to the effect of the 1-alkene based side groups on the dynamics of polymer chains. The present work would be helpful to understand the chain stiffness based polymer dynamics and processing of polyolefins and copolymers prepared with the metallocene catalyst.

Equilibrium Melting Temperature of the Hexagonal Crystals of Polybutene-1 and Its Copolymer

TheLamellar structures of form I in polymorphic isotactic polybutene-1 (iPB-1) and forms I and I′ in butene-1/ethylene random copolymer (iPB-1/C2) were investigated by studying their melting behavior using the combination of small-angle X-ray scattering (SAXS) and fast scanning chip calorimetry (FSC) techniques. Hexagonal form I was transformed from tetragonal form II obtained by crystallization of a homogeneous melt of iPB-1 and iPB-1/C2. Hexagonal form I′ was crystallized directly from a heterogeneous melt of iPB-1/C2. Despite the same hexagonal crystallographic structure, forms I and I′ have obviously distinct melting behaviors due to different ways of crystal formation. Well-defined linear dependences of the melting temperature against the reciprocal lamellar thickness were observed for forms I and I′ with frozen chain mobility in crystals. The slopes of the thus obtained melting lines for forms I and I′ are different. Their extrapolations to imaginary infinitely large lamellar thickness provide the equilibrium melting temperature Tm∞ for forms I and I′, which is associated with the stability of the lamellar crystals. In spite of crystal defects in form I′, a higher Tm∞ is observed for this form in iPB-1/C2 than Tm∞ for form I in both iPB-1 and iPB-1/C2. The difference in Tm∞ indicates a less perfect structure of form I crystal lamellae that is caused by the fragmentation of form II crystal lamellae during the polymorphic phase transition from form II to I. The lamellae broke into crystal blocks along the lamellar direction. The smaller lateral sizes of the fragmented lamellae clearly induce a decrease in the stability of crystals, as expressed in a lower Tm∞ for form I.

Ethylene Comonomer-Directed Epitaxial Nucleation and Growth of β-Nucleated Isotactic Polypropylene

We present a molecular-level investigation of the epitaxial crystallization of β-nucleated isotactic polypropylene associated with the minor and local topographic modification at the interface, i.e., the inclusion of an ethylene comonomer. The experimental results show that the relative fraction of β-crystal (Kβ) decreases progressively with increasing the amount of ethylene comonomer, which originates from a simultaneous reduction in the β-nucleation ability of a β-nucleating agent (N,N′-dicyclohexylterephthalamide, DCHT) toward propylene–ethylene random copolymers (PERs) and the growth rate of the β-crystal relative to the α-crystal. With the aid of molecular mechanics simulation, we demonstrate that such a topographic modification weakens the intermolecular interactions at the nucleation and growth interfaces, thereby modifying the epitaxial nucleation of the β-crystal and the growth kinetics of β- and α-crystals. The study reveals that the polymorph selection of the PERs/DCHT system is not solely determined by the lattice match but also profoundly influenced by the topography characteristics dependence of molecular interaction at the crystalline interfaces. Our fundamental insight could have important implications in the control of the polymorphism of polymers through the careful design of the topography of the nucleation and growth interfaces.

Raman spectroscopic analysis of encapsulants in aged photovoltaic modules

The aging of an encapsulation material of a random copolymer of ethylene and vinyl acetate (EVA), in outdoor-exposed (OE) crystalline-silicon (c-Si) photovoltaic (PV) modules was investigated through nondestructive Raman spectroscopy. The effect of water vapor (WV) on the Raman spectra of EVA encapsulants in c-Si PV modules was also investigated after long-term damp-heat (DH) tests at 85 °C and 85 % relative humidity. The EVA encapsulants in the long-term OE modules showed two different shapes and intensities of broad Raman spectra due to the increased intensity of the fluorescence background (FB). The encapsulants at the center of c-Si solar cells in the long-term OE modules showed a high intensity of FB, which increased with the exposure time. On the other hand, the Raman spectra of the encapsulant at the edge of the c-Si solar cells resembled those of the DH-exposed (DHE) modules, with a similar shape and lower intensity of FB than at the center. The spectral results indicate that the encapsulants at the edge were affected by WV, similar to the same as the DHE condition. The DHE-type Raman spectra for the EVA encapsulants at the edge of c-Si solar cells in OE modules show that the acetic acid may be formed from the EVA encapsulants by WV, resulting in corrosion of finger electrodes on c-Si solar cells and consequently diminishing the performance of the modules.

Structural evolution of mesomorphic propylene–1‐butene random copolymer during heating process

AbstractThe study of the transition of mesophase to α‐crystal (meso–α transition) is of great significance for understanding the crystallization, morphology as well as processability of polypropylene materials. The structural evolution of mesomorphic isotactic propylene–1‐butene (iPPBu) random copolymer during the continuous heating process was investigated using in situ Fourier transform infrared spectroscopy, differential scanning calorimetry, wide‐angle X‐ray diffraction and dynamic mechanical analysis. The presence of the butene comonomer influences the meso–α transition behavior. Compared with the mesomorphic iPP homopolymer, the presence of butene comonomer reduces both onset temperature (Tonset) and end temperature (Tend) of the meso–α transition, and narrows the transition temperature range. The content of the 31 helical sequence with 12 monomers remains invariant during the meso–α transition, differing from that of mesomorphic iPP homopolymer. Similar to mesomorphic iPP homopolymer, the 31 helical sequence with monomer number n ≤ 12 is found to exist in the rigid amorphous fraction of iPPBu, but is different from that of a mesomorphic propylene–ethylene random copolymer. In the meso–α transition (from 60 to 100 °C), the redshift of the peak position of the band at ca 841 cm−1 provides new information for the approaching of adjacent stems at the molecular level. Moreover, a new peak at around Tend is found in the tan(δ)–T plot, and is correlated with the meso–α transition. The activation energy of the meso–α transition of mesomorphic iPPBu is 32.5 kJ mol−1, which is slightly lower than that of mesomorphic iPP homopolymer. This work sheds new light on further understanding of the meso–α transition mechanism of iPPBu copolymer at the molecular level and elucidates the effect of butene comonomer on the meso–α transition. © 2021 Society of Industrial Chemistry.

Peculiar self‐nucleation behavior of a polybutene‐1/ethylene random copolymer

The self-nucleation behavior of a polybutene-1/ethylene random copolymer, P(B1-ran-E), which undergoes a complex crystal-crystal transition behavior, has been studied in detail. Similar to PE random copolymers, this material shows a strong melt memory effect even above equilibrium melting point of PB-1 homopolymer. Different polymorphic forms can be obtained when P(B1-ran-E) is cooled from different self-nucleation domains. The trigonal form I′ could only be nucleated in the presence of remaining form I crystals via self-seeding, while the melt memory in Domain IIa could only act as self-nuclei for kinetically favored form II. Furthermore, observations from optical microscopy illustrated that melt memory is able to enhance nucleation density but it does not affect the spherulitic growth rate.

Durable crystalline silicon photovoltaic modules based on breathable structure

The long-term durability of crystalline silicon (c-Si) photovoltaic (PV) modules was investigated by long-term damp-heat (DH) tests at 85 °C with 85% relative humidity. Breathable module structure using front or rear materials with low-barrier properties markedly improved the long-term DH resistance of c-Si PV modules. No corrosion of finger electrodes on c-Si solar cells occurred by diffusion of acetic acid, which was formed from an encapsulant of a random copolymer of ethylene and vinyl acetate (EVA) towards the outside of the modules by the breathable structure. Raman spectroscopy data indicated that degradation of the EVA encapsulants including additives (e.g. UV absorber) were suppressed by the usage of a breathable front film compared to a front cover glass used for the conventional modules. The breathable modules based on low-barrier components would improve the long-term photochemical and chemical durability of c-Si PV modules further to achieve 40 year operation.

Change of lamellar morphology upon polymorphic transition of form II to form I crystals in isotactic Polybutene-1 and its copolymer

Morphology and domain sizes in isotactic polybutene-1 homopolymer (iPB-1) and (butene-1)-ethylene random copolymer (iPB-1/C2) are studied by spin-diffusion time-domain 1H NMR and SAXS experiments. Lamellar thickness is smaller for iPB-1/C2 than for iPB-1 and decreases with decreasing crystallization temperature. iPB-1/C2 with form I’ crystals, which were directly formed upon crystallization from a heterogeneous melt, has typical for polyolefins lamellar morphology with the crystal-amorphous interface that separates crystal lamellae and interlamellar amorphous domains. Different lamellar structure is observed in iPB-1 and iPB-1/C2 with form I crystals which were obtained upon polymorphic phase transition from form II to form I crystals. The phase transition causes fragmentation of crystal lamellae into small blocks with a wide size distribution as was shown by the NMR method. Two types of the interface are present in these samples: the inner interface that separates crystal blocks within fragmented crystal lamellae, and the crystal-amorphous interface on the surface of fragmented lamellae. The molecular mechanism of polymorphic form II to form I phase transition is proposed. High chain mobility in form II crystals and chain folding structure on the lamellar surface play significant role at the initial and final stages of the restructuring of crystal lamellae during the phase transition, respectively.

Spectroscopic investigation of long-term outdoor-exposed crystalline silicon photovoltaic modules

Degradations of an encapsulant of a random copolymer of ethylene and vinyl acetate (EVA), in long-term outdoor-exposed (OE) crystalline silicon (c-Si) photovoltaic (PV) modules were investigated by Raman and Fourier transform-infrared (FT-IR) spectroscopy measurements. Two predominant chemical and photochemical degradations, discoloration (yellow-browning) and formation of acetic acid (AcOH), were observed in EVA encapsulants in c-Si PV modules exposed outdoors for approximately 27 years in Japan (Kirishima module). The yellow-browning of the encapsulants was suggested to be due to reaction of additives, such as UV absorbers that were incorporated in the encapsulants, because no marked degradation of EVA itself was observed in the FT-IR absorption spectrum. Contrastingly, the absorption intensity of C = O of the colorless EVA in the Kirishima module decreased to 70 %, which was similar to that for the encapsulant in a damp-heat-tested (DHT) module at 85 °C with 85 % relative humidity for 4000 h (68 %), suggesting that AcOH was formed from EVA. The degradation mechanisms of the EVA encapsulants in long-term OE and DHT c-Si PV modules were explored by spectroscopy and other analyses.

A Facile and Efficient Method for Preparing Chain Extended Poly(lactic acid) Foams with High Volume Expansion Ratio

In recent years, poly(lactic acid) (PLA) foams have drawn considerable attention worldwide due to their environmental friendliness and excellent biocompatibility. However, it was a big challenge to prepare PLA foams with high volume expansion ratio owing to their poor crystallization properties and melt strength. In this work, the random copolymer of ethylene and glycidyl methacrylate as an efficient chain extender (CE) was chosen and employed to improve the crystallization behaviors and foamability of PLA. The chain extension reaction between PLA and CE was proved by torque curves, Fourier transform infrared spectra, gel fraction, and intrinsic viscosity measurements. Differential scanning calorimetry results and polarized optical microscope images showed that the crystallinity and spherocrystal number of various PLA samples increased notably as well as their spherocrystal size decreased with the CE content increasing. The viscoelasticity of various PLA samples was improved by the increment in the CE content. Various PLA samples were foamed by a batch foaming method at different foaming temperature with supercritical CO2 to research the influence of crystallization behaviors and/or rheological properties on the foaming behaviors of PLA. At the high foaming temperature, the cell density and volume expansion ratio (VER) of various PLA foams were affected by rheological properties significantly and their highest VER could reach to 42.41 ± 0.01 times. At the low foaming temperature, the cellular morphology of various PLA foams was improved notably, due to the increased melt strength induced by the cooling and the generation of crystallization region.

Eco-Friendly Approach and Potential Biodegradable Polymer Matrix for WPC Composite Materials in Outdoor Application

Blends based on high-density polyethylene (HDPE) and poly(lactic) acid (PLA) with different ratios of both polymers were produced: a blend with equal amounts of HDPE and PLA, hence 50 wt.% each, proved to be a useful compromise, allowing a high amount of bioderived charge without this being too detrimental for mechanical properties and considering its possibility to biodegradation behaviour in outdoor application. In this way, an optimal blend suitable for producing a composite with cellulosic fillers is proposed. In the selected polymer blend, wood flour (WF) was added as a natural filler in the proportion of 20, 30, and 40 wt.%, considering as 100 the weight of the polymer blend matrix. There are two compatibilizers to modify both HDPE-PLA blend and wood-flour/polymer interfaces, i.e., polyethylene-grafted maleic anhydride and a random copolymer of ethylene and glycidyl methacrylate. The most suitable percentage of compatibilizer for HDPE-PLA blends appears to be 3 wt.%, which was selected also for use with wood flour. In order to evaluate properties of blends and composites tensile tests, scanning electron microscopy, differential scanning calorimetry, thermogravimetric analyses, and infrared spectroscopy have been performed. Wood flour seems to affect heavy blend behaviour in process production of material suggesting that future studies are needed to reduce defectiveness.

Stretching behavior of the butene‐1/ethylene random copolymer: A direct correspondence between triggering of II‐I phase transition and mechanical yielding

Quiescent phase transition from the tetragonal form II into hexagonal form I was utilized to prepare II/I mixture systems in the butene-1/ethylene random copolymer with 1.5 mol% ethylene units, where aging duration was varied to tune the fraction of form I in the initial crystallites. The mechanical test and in-situ wide-angle X-ray diffraction were combined to quantitatively explore stretching-induced phase transition of the II/I mixture systems. Interestingly, the triggering of stretching-induced further phase transition from forms II to I always corresponds to its mechanical yielding. This may be associated to formation of new tie chains by the lamellar collapsing with yielding. Moreover, for all mixture systems, the threshold stresses for triggering phase transition, that is, the yield stress, follow the master form I fraction-stress correlation that is obtained from the pure initial form II system. Such form I fraction-stress correspondence confirms the stress-determined kinetics for phase transition and also provides an approach to predict the yielding stress for the II/I mixture system.

Optimization of Thermoplastic Blend Matrix HDPE/PLA with Different Types and Levels of Coupling Agents.

High-density polyethylene (HDPE) and poly(lactic) acid (PLA) blends with different ratios of both polymers, namely, 30:70, 50:50, and 70:30, were produced. Polyethylene-grafted maleic anhydride and a random copolymer of ethylene and glycidyl methacrylate were also considered as compatibilizers to modify HDPE/PLA optimal blends and were added in the amounts of 1, 3, and 5 wt.%. Different properties of the blends were evaluated by performing tensile tests and scanning electron microscopy to analyze blend and interfaces morphology. Moreover, thermomechanical analysis through differential scanning calorimetry, thermo-gravimetric analysis, and infrared spectroscopy were also performed. The blend containing equal amounts of HDPE and PLA seemed to present a good balance between amount of bio-derived charge and acceptable mechanical properties. This suggests that these blends have a good potential for the production of composites with lingo-cellulosic fillers.

Stretching‐induced phase transition of the butene‐1/ethylene random copolymer: Orientation and kinetics

ABSTRACTThe stretching‐induced phase transition from tetragonal Form II to hexagonal Form I and the evolution of corresponding crystallite orientation were studied for the butene‐1/ethylene random copolymer with 1.5 mol % ethylene by using a combination of tensile test and in situ wide‐angle X‐ray diffraction. Three orientation pathways were distinguished for II‐I phase transition, including phase transition accomplishing within off‐axis oriented crystallites (Orientation Pathway 1), phase transition with simultaneous formation of highly oriented crystallites (Orientation Pathway 2), and phase transition occurring within the highly oriented crystallites already formed (Orientation Pathway 3). The kinetics of II‐I transition was correlated with the macroscopic mechanical response, which exhibits a strong dependence on orientation. In Orientation Pathway 1, the triggering of phase transition corresponds to the mechanical yielding. More interestingly, the kinetics of transition exhibits the identical dependence on stress. However, in Orientation Pathways 2 and 3, appearance of the highly oriented crystallites substantially alters transition kinetics, which is tentatively associated with the stress bearing by interstack tie chains. © 2018 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2019, 57, 116–126

Morphology and properties in the binary blends of polypropylene and propylene–ethylene random copolymers

Propylene-based random copolymers copolymerized by propylene and ethylene (PEC) with low degree of crystallinity were used for the modification of isotactic polypropylene (PP) in this work. The phase morphology, miscibility, mechanical properties and rheological properties of the PP/PEC blends were systematically investigated. Dynamic mechanical analysis (DMA) and differential scanning calorimeter (DSC) results verified that the blends were partial miscibility. This may be due to the fact that the PP segments from PEC chains are incorporated into crystal lattice of neat PP, and they together act as a matrix of the PP/PEC blends. The rest of the PEC chains serve as the dispersed phase. The segments from the PEC chains incorporated into pure PP play the role of compatibilizer between the PP matrix and the dispersed phase, which make the dispersed phase to be uniformly dispersed in the PP matrix, resulting in an increase in impact strength from 5 kJ/m2 of neat PP to 40 kJ/m2 of blend with 20 wt% PEC. In addition, the viscosity and modulus of the blends were lower than that of pure PP due to the dilution of PEC in the molten state.

Interactions between PLA, PE and wood flour: effects of compatibilizing agents and ionic liquids

AbstractThe differences in hydrophilicity are a main drawback for wood polymer composites (WPCs). This work aims at compatibilizing bio-derived poly(lactic acid) (PLA), high density polyethylene (PE) and wood fibers (WFs) with either functional PEs [PE-graft-maleic anhydride (MA) (Polybond 3029) or random copolymer of ethylene and glycidyl methacrylate (PE-g-GMA) (Lotader AX8840)] or trihexyl(tetradecyl)phosphonium bistriflamide ionic liquid (IL). The interactions and possible chemical reactions between PLA and functional PE or IL were studied including their mechanical properties. PE-g-GMA significantly increased elongation at break of PLA. According to scanning electron microscopy (SEM), the latter also displays good compatibility with WF. Addition of IL plastifies PLA without degrading it and improves the thermal stability of WF.

Mechanism of Significant Improvement of Large Strain Elasticity in Soft Propylene–Ethylene Random Copolymer via Blending with Hard Propylene–Ethylene Coplymer

The deformation behavior of propylene–ethylene copolymers with 23 mol % of ethylene (iPPcoE23) and its blend (90/10 w/w) (iPPcoE23b) with propylene–ethylene copolymer (6 mol % ethylene) (iPPcoE6) at room temperature was studied by in situ small-angle X-ray scattering and wide-angle X-ray diffraction techniques. The 10 wt % copolymer with 6 mol % ethylene counits dispersed as small domains in the matrix of iPPcoE23. During stretching, longer and thinner fibrils and better elasticity properties were shown in the blend iPPcoE23b at large strain regime. The higher elasticity for iPPcoE23b at large strain regime was ascribed to the weak ability of strain-induced crystallization due to cocrystallization of the crystallizable long chain sequences of iPPcoE23 with the high crystalline iPPcoE6 during cooling, leaving fewer long crystallizable sequences in the matrix in iPPcoE23b. In addition, the phase-separated domains contributed stronger network modulus in the late stage of stretching compared with that of the ...

Studies on the effect of compatibilizers on mechanical, thermal and flow properties of polycarbonate/poly (butylene terephthalate) blends

Bisphenol-A polycarbonate (PC) and poly(butylene terephthalate) (PBT) were melt blended with ethylene-n-butylacrylate-glycidylmethacrylate terpolymer (E-BA-GMA) at various proportions in order to study the effects of compatibilizers on mechanical, thermal and flow properties of blends. Furthermore, on the basis of this study, PC and PBT were melt-blended at 60/40 proportion with three different compatibilizers viz., ethylene-n-butylacrylate copolymer (E-BA), E-BA-GMA and random copolymer of ethylene and glycidylmethacrylate (E-GMA) at 3 phr loading in a co-rotating twin screw extruder. Tensile, flexural and impact tests were carried out on injection molded samples of PC/PBT blends. The notched izod impact strength increases enormously (∼2–3 times) on addition of any one of the three compatibilizers, and elongation at break (%) also improves tremendously (3, 5 and 4 times) on incorporation of E-BA, E-BA-GMA and E-GMA copolymer, respectively while other mechanical properties decreases slightly (3%–8%) on addition of any one of these compatibilizers. The heat deflection temperature (HDT) raises ∼8 °C–9 °C on addition of either E-BA-GMA or E-GMA, while E-BA shows a negative effect on HDT. The melt flow index diminishes significantly (∼5%–20%) on incorporation of these compatibilizers. The morphology studies via scanning electron microscopy of these four blends were carried out to confirm the mechanical results.

Counits Content and Stretching Temperature-Dependent Critical Stress for Destruction of γ Crystals in Propylene-Ethylene Random Copolymers.

Tensile deformation behavior of three random propylene–ethylene copolymers with the same molecular weight and different contents of counit was investigated at different temperatures from room temperature to close to melting point via tensile tests, step-cycle tests, and in situ wide-angle X-ray diffraction techniques. Upon stretching, the original crystalline lamellae must be destroyed, generating new highly oriented ones. A critical stress has been suggested, under which the original crystallites can be destructed. The propylene–ethylene copolymer samples in pure γ-form transformed gradually into α-form during tensile stretching. This crystalline transition proceeded via a destruction (melting) of the original γ-form crystals followed by recrystallization of the freed polymeric chain segments into α-form along stretching direction. This result provides a marker for investigating the critical stress mentioned above. Such critical stresses triggering the destruction of γ-form crystals for the propylene–ethylene copolymers of different ethylene counit contents were successfully calculated. It turned out that this critical stress depended on the ethylene counit content and stretching temperature. Samples with less ethylene counits show higher critical stress because of a lower degree of insertion of the ethylene counits into the crystalline unit cell than samples with higher ethylene counit content. The critical stresses remained constant when the samples were stretched at low-temperature region, whereas they decreased significantly at high stretching temperatures close to the melting points due to strong thermal distortion of the crystalline lattices, making the crystallites less stable.