Differential scanning calorimetry of copolymer of isotactic polypropylene backbone with grafted poly(ethylene‐co‐propylene) branches

A series of graft polymers having polypropylene (PP) backbone and poly(ethylene‐co‐propylene) (EPR) side chains was prepared. PP backbone molecular weight (M_n) was 28–98 kg/mol, EPR side chain M_n was 2.6–17 kg/mol, and EPR content was 0–16 wt %. In this work, thermal analysis of the copolymers was performed using differential scanning calorimetry (DSC). Nonisothermal crystallization was performed at different cooling rates. The DSC thermograms revealed multiple melting peaks for slowly cooled samples, most likely the result of the melting of thinner tangential lamellae followed by the melting of thicker radial lamellae. Equilibrium melting temperature (T_m⁰) was determined using the linear Hoffman–Weeks method. Another approach was also used for determining T_m⁰: melting temperature (T_m) and crystallization temperature (T_c) were plotted as functions of logarithmic cooling rate. Linear relationships were observed for all samples with the cross points as T_m⁰'s. As cooling rate decreased, T_c, T_m, and enthalpy of fusion (ΔH_f) increased. T_m and T_m⁰ increased with increasing PP M_n. T_c and T_m were unaffected by the grafting of EPR onto the PP backbone. T_m⁰ and ΔH_f decreased as EPR content increased. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 99: 3380–3388, 2006     

Solvothermal process for grafting dibutylmaleate onto poly(ethylene‐co‐1‐octene)

Solvothermal process was successfully developed to graft dibutylmaleate (DBM) onto poly(ethylene‐co‐1‐octene) (POE) with dicumyl peroxide (DCP) as free radical‐initiator. FTIR spectra demonstrate that DBM is successfully grafted onto the backbone of POE by this novel method. The influences of DBM content, DCP concentration, POE concentration, reaction temperature and reaction time on the grafting copolymerization have been investigated in detail through grafting degree (GD). It is worthy to indicate that high grafting degree (above 15%) can be achieved through the one‐pot way when the graft reaction is carried out in 40 mL toluene at 150°C for 5 h with 1.6 g DBM, 6–8 g POE and 0.35 g DCP. This developed solvothermal process is becoming an effective way to prepare POE‐g‐DBM graft copolymers, and can be extended to other systems. In addition, TGA results show that the thermal properties of POE are enhanced after the grafting reaction. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Study on the melt fracture of metallocene poly(ethylene‐octene) in capillary flow

Shear viscosity and melt fracture of a metallocene poly(ethylene‐octene) were studied using a capillary rheometer and dies with different lengths. The true wall shear stresses determined at zero die length showed a dip at high shear rates. The shear viscosity was derived from the true wall shear stress. With increasing shear rates, the extrudate staged from smooth to three types of melt fracture with regular patterns, and then turned into irregular shapes. Three types of regular melt fractures—sharkskin, helix, and spiral (in sequence)—were observed with an increase of the shear rates. The wavelength of the regular melt fracture was measured from extrudates, and the corresponding frequency was calculated. The frequency increased at elevated melt temperatures. Both shear viscosity and frequency at different temperatures correlated well by using the time–temperature Williams–Landel–Ferry (WLF) superposition. Additionally, it was found that the frequency decreased slightly for a longer die but it increased when the shear rate went up. Three frequency functions were associated with three melt fracture patterns, respectively. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 98: 903–911, 2005     

Crystallization kinetics of poly(1,4‐butylene‐co‐ethylene terephthalate)

The crystallization kinetics of poly(butylene terephthalate) (PBT), poly(ethylene terephthalate) (PET), and their copolymers poly(1,4‐butylene‐co‐ethylene terephthalate) (PBET) containing 70/30, 65/35 and 60/40 molar ratios of 1,4‐butanediol/ethylene glycol were investigated using differential scanning calorimetry (DSC) at crystallization temperatures (T_c) which were 35–90 °C below equilibrium melting temperature . Although these copolymers contain both monomers in high proportion, DSC data revealed for copolymer crystallization behaviour. The reason for such copolymers being able to crystallize could be due to the similar chemical structures of 1,4‐butanediol and ethylene glycol. DSC results for isothermal crystallization revealed that random copolymers had a lower degree of crystallinity and lower crystallite growth rate than those of homopolymers. DSC heating scans, after completion of isothermal crystallization, showed triple melting endotherms for all these polyesters, similar to those of other polymers as reported in the literature. The crystallization isotherms followed the Avrami equation with an exponent n of 2–2.5 for PET and 2.5–3.0 for PBT and PBETs. Analyses of the Lauritzen–Hoffman equation for DSC isothermal crystallization data revealed that PBT and PET had higher growth rate constant G_o, and nucleation constant K_g than those of PBET copolymers. © 2001 Society of Chemical Industry     

The effectiveness of magnesium carbonate‐based flame retardants for poly(ethylene‐co‐vinyl acetate) and poly(ethylene‐co‐ethyl acrylate)

In this report we outline recent work on the evaluation of magnesium carbonate‐based flame retardants for polymers commonly used in halogen‐free flame retardant wire and cable applications: poly(ethylene‐co‐vinyl acetate) (EVA) and poly(ethylene‐co‐ethyl acrylate) (EEA). Natural magnesium carbonate (magnesite), synthetic magnesium carbonate (hydromagnesite), and hydromagnesite/huntite blends were combined with EVA or EEA and tested for flame retardancy effectiveness with the cone calorimeter. The flammability results showed that the effectiveness of these carbonates was polymer dependent, suggesting that polymer degradation chemistry played a role in the flammability reduction mechanism. Hydromagnesites were, in general, more effective in reducing flammability, being comparable in performance to magnesium hydroxide. Finally, we report some polymer–clay (organically treated montmorillonite and magadiite) + magnesium carbonate flame retardant results which showed that the nanocomposite yielded mixed results. Specifically, the polymer–clay nanocomposite samples did not always yield the greatest reductions in peak heat release rate. Copyright © 2007 John Wiley & Sons, Ltd.     

Rheological and thermal properties of binary blends of polypropylene and poly(ethylene‐CO‐1‐octene)

Dynamic viscoelastic properties of binary blends consisting of an isotactic polypropylene (i‐PP) and ethylene‐1‐octene copolymer (PEE) were investigated to reveal the relation between miscibility in the molten state and the morphology in the solid state. In this study, PEE with 24 wt % of 1‐octene was employed. The PEE/PP blend with high PEE contents showed two separate glass‐relaxation processes associated with those of the pure components. These findings indicate that the blend presents a two‐phase morphology in the solid state as well as in the molten state. The PEE/PP blend with low PEE content showed a single glass‐relaxation process, indicating that PEE molecules were probably incorporated in the amorphous region of i‐PP in the solid state. The DMTA analysis showed that the blends with low PEE contents presented only one dispersion peak, indicating a certain degree of miscibility between the components of these blends. These results are in accordance with the results of the rheological analysis. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 79: 1634–1639, 2001     

Reactive blending of poly(L‐lactic acid) with poly(ethylene‐co‐vinyl alcohol)

Poly(L ‐lactic acid) (PLLA) was blended with poly(ethylene‐co‐vinyl alcohol) (EVOH) in the presence of an esterification catalyst to induce reaction between the hydroxyl groups of EVOH and the terminal carboxylic group of PLLA. Nascent low‐molecular‐weight PLLA, obtained from a direct condensation polymerization of L ‐lactic acid in bulk state, was used for the blending. Domain size of the PLLA phase in the graft copolymer was much smaller than that corresponding to a PLLA/EVOH simple blend. The mechanical properties of the graft copolymer were far superior to those of the simple blend, and the graft copolymer exhibited excellent mechanical properties even though the biodegradable fraction substantially exceeded the percolation level. The grafted PLLA reduced the crystallization rate of the EVOH moiety. Melting peak temperature (T_m) of the PLLA phase was not observed until the content of PLLA in the graft reaction medium went over 60 wt %. The modified Sturm test results demonstrated that biodegradation of EVOH‐g‐PLLA took place more slowly than that of an EVOH/PLLA simple blend, indicating that the chemically bound PLLA moiety was less susceptible to microbial attack than PLLA in the simple blend. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 98: 886–890, 2005     

Optimization of engineering and solvent resistive behavior of high vinyl acetate content EVA‐modified poly(ethylene‐co‐1‐octene) interpenetrating network blends using taguchi orthogonal array

Process parameters of poly (ethylene‐co‐vinyl acetate) (EVA)‐modified poly (ethylene‐co‐1‐octene) (POE)‐interpenetrating, double network blend was designed through Taguchi L9 orthogonal array as a novel approach for complete optimization of engineering and solvent‐swelling properties. Influence of different factors like EVA and peroxide concentrations, blending temperature, and blending time on gel content, tensile modulus, tensile strength, ultimate elongation were statistically calculated. Results showed good correlation between mathematical and physical inferences. Stress relaxation, hysteresis and other physico‐mechanicals like total elongation, solvent‐swelling, etc., were interestingly depended upon the nature of dominantly crosslinked phase instead of net crosslinking of the network hybrids. Sorption, on the other hand, depended on the hydrophobic‐hydrophilic property of the surfaces. The series of data produced finally helped to select the best process parameters under which a particular POE‐EVA blend composition yielded most balanced physico‐mechanicals. © 2012 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

Miscibility of poly(3‐hydroxybutyrate‐co‐3‐hydroxyvalerate) with high molecular weight poly(lactic acid) blends determined by thermal analysis

An important strategy used in the polymer industry in recent years is blending two bio‐based polymers to attain desirable properties similar to traditional thermoplastics, thus increasing the application potential for bio‐based and bio‐degradable polymers. Miscibility of poly(3‐hydroxybutyrate‐co‐3‐hydroxyvalerate) (PHBV) with poly(L ‐lactic acid) (PLA) were characterized using differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), and scanning electron microscopy (SEM). Three different grades of commercially available PLAs and one type of PHBV were blended in different ratios of 50/50, 60/40, 70/30, and 80/20 (PHBV/PLA) using a micro‐compounder at 175°C. The DSC and TGA analysis showed the blends were immiscible due to different stereo configuration of PLA polymer and two distinct melting temperatures. However, some compatibility between PHBV and PLA polymers was observed due to decreases in PLA's glass transition temperatures. Additionally, the blends do not show clear separation by SEM analysis, as observed in the thermal analysis. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

Influence of hydrogen donors on peroxide‐initiated melt grafting of vinylsilane to poly(ethylene‐co‐vinyl acetate)

A technique has been examined for reducing the extent of crosslinking resulting from 1,1‐di(t‐butylperoxy)‐3,3,5‐trimethylcyclohexane (L‐231) initiating melt grafting of vinyltriethoxysilane (VTEOS) onto poly(ethylene‐co‐vinyl acetate) (EVA). Using measurements of crosslink density and VTEOS conversion, a standard of selectivity for the EVA/VTEOS/L‐231 system at 145 °C was defined and used to assess the influence of a range of additives (0.25 mol per mole VTEOS). The data indicated that compounds such as 4‐nonene, N,N‐dimethylaniline, and cumene improve reaction selectivity, whereas dodecane and cyclohexyl acetate have no effect. A strong correlation between the minimum C? H bond dissociation energy and the influence of a given compound is evident, suggesting that a labile C? H bond is the key element of an effective additive. A mechanism of additive function on the basis of hydrogen atom donation is proposed. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 83: 2397–2402, 2002     

Compatibility of low‐density polyethylene/poly(ethylene‐co‐vinyl acetate) binary blends prepared by melt mixing

The compatibility of low‐density polyethylene and poly(ethylene‐co‐vinyl acetate) containing 18 wt % vinyl acetate units (EVA‐18) was studied. For this purpose, a series of different blends containing 25, 50, or 75 wt % EVA‐18 were prepared by melt mixing with a single‐screw extruder. For each composition, three different sets of blends were prepared, which corresponded to the three different temperatures used in the metering section and the die of the extruder (140, 160, and 180°C), at a screw rotation speed of 42 rpm. Blends that contained 25 wt % EVA‐18 were also prepared through mixing at 140, 160, or 180°C but at a screw speed of 69 rpm. A study of the blends by differential scanning calorimetry showed that all the prepared blends were heterogeneous, except that containing 75 wt % EVA‐18 and prepared at 180°C. However, because of the high interfacial adhesion, a fine dispersion of the minor component in the polymer matrix was observed for all the studied blends with scanning electron microscopy. The tensile strengths and elongations at break of the blends lay between the corresponding values of the two polymers. The absence of any minimum in the mechanical properties was strong evidence that the two polymers were compatible over the whole range of composition. The thermal shrinkage of the blends at various temperatures depended mainly on the temperature and EVA‐18 content. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 90: 841–852, 2003     

Viscoelasticity and morphology of poly(ethylene‐co‐vinyl acetate)/polyisobutylene blends

Blends of an ethylene/vinyl acetate copolymer (EVA) and polyisobutylene of various compositions were prepared by mechanical mixing at a temperature above the melting point of EVA (T_m^EVA) but below the upper critical solution temperature of 170°C for given blends. The rheological properties of the components and blends were studied in the region of small‐amplitude oscillating deformation at temperatures above and below T_m^EVA in the frequency range of 0.01–100 rad/s. At temperatures lower than T_m^EVA, the rheological properties were determined by the existence of the yield stress. With diminishing frequency, the viscosity increased, and the plateau in the relaxation spectrum at low frequencies broadened. The morphology of the blends depended on the conditions of sample heating. The introduction of a finely dispersed filler into the blends led to an anomalous drop in the viscosity. The morphology of the systems that arose by mechanical blending of the molten components was the important factor in the rheological behavior. The observed effects were examined in the framework of the concept of structural networks formed in melts by nonmelted crystallites of EVA. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 102: 2700–2707, 2006     

Synthesis and characterization of biodegradable block copolymers of poly(propylene fumarate‐co‐sebacate)‐co‐poly(ethylene glycol) and poly(ethylene fumarate‐co‐sebacate)‐co‐poly(ethylene glycol)

The synthesis of two low molecular weight linear unsaturated oligoester precursors, poly(propylene fumarate‐co‐sebacate) (PPFS) and poly(ethylene fumarate‐co‐sebacate) (PEFS), are described. PPFS, PEFS, and poly(ethylene glycol) are then used to prepare poly(propylene fumarate‐co‐sebacate)‐co‐poly(ethylene glycol) (PPFS‐co‐PEG) and poly(ethylene fumarate‐co‐sebacate)‐co‐poly(ethylene glycol) (PEFS‐co‐PEG) block copolymers. The products thus obtained are investigated in terms of the molecular weight, composition, structure, thermal properties, and solubility behavior. A number of design parameters including the molecular weights of PPFS, PEFS, and PEG, the reaction time in the polymer synthesis, and the weight ratio of PEG to PPFS or to PEFS are varied to assess their effects on the product yield and properties. The hydrolytic degradation of PPFS‐co‐PEG and PEFS‐co‐PEG in an isotonic buffer (pH 7.4, 37°C) is investigated, and it is found that the fumarate ester bond cleaves faster than does the sebacate ester bond. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 92: 295–300, 2004     

Thermal stability of poly(ethylene‐co‐trimethylene terephthalate)s

The thermal stability of poly(ethylene‐co‐trimethylene terephthalate) was first studied by thermogravimetry under nitrogen atmosphere at different heating rates. The results showed that the thermal behavior of the copolyester had a strong dependence on the chemical composition. The average activation energy from Ozawa technique increases with the concentration of EG units in the polyester, and a greater TG concentration in the copolyesters would decrease the onset degradation temperature. These phenomena may be attributed to the presence of one more methylene of TG unit than of EG in the copolymer. It is also noted that the yield of solid residue increases with the concentration of EG units in the polymer chain at any heating rate, which may be associated with the content of aromatic ring in the polymer chain. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 101: 3330–3335, 2006     

Crystallization behavior and mechanical properties of polypropylene random copolymer/poly(ethylene‐octene) blends

New polymer blends of polypropylene random copolymer (PP‐R) and poly(ethylene‐octene) (POE) were prepared by melt‐blending process using a corotating twin‐screw extruder. The POE content was varied up to 35%. The toughening efficiency of POE for PP‐R was evaluated by the mechanical properties of the resulted PP‐R/POE blends. The crystallization behavior and morphology of the blends were also studied. Results show that POE acts as nucleation agent to induce the crystallization of PP‐R matrix at higher crystallization temperature. Super‐toughened PP‐R/POE blends (Izod impact strength more than 500 J/m) can be readily achieved with only 10 wt % of POE. The high toughness of PP‐R/POE is attributed to cavitation and shear yielding of matrix PP‐R, as revealed by the morphology studies. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Comparison of the enthalpic relaxation of poly(lactide–co‐glycolide) 50:50 nanospheres and raw polymer

The phenomenon of enthalpic relaxation was evaluated for poly(lactide‐co‐glycolide) (PLGA, 50:50), in terms of storage of nanospheres for use as a controlled drug delivery system. Samples were stored for different times and temperatures below the glass transition temperature (T_g). Relaxation occurred at a significant rate up to 15 degrees below the T_g of 39.2°C. The effect of polymer morphology was considered by comparing the relaxation kinetics of the raw polymer with that of nanospheres formed using a novel technique. The nanospheres were shown to have a larger change in heat capacity at the glass transition and a longer average relaxation time than that of the raw polymer, and the relationship between these two parameters was discussed. For both the raw polymer and the nanospheres, relaxation was found to occur at a significant rate at room temperature. The storage of this system at subambient temperatures was therefore deemed important for maintaining the physicochemical properties of the system. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 86: 1868–1872, 2002     

Morphology and texture development of uniaxially stretched poly(ethylene naphthalene‐2,6‐dicarboxylate)

The texture development of PEN films with different semicrystalline morphologies have been studied by X‐ray diffraction. These different structures have been obtained by uniaxially stretching PEN amorphous films at 100 and 160°C (below and above T_g) at different drawing ratios. Samples have also been characterized by DSC to determine the crystallinity ratios, the crystallization, and melting temperatures. To define the orientation of crystallites in the oriented samples, pole figures have been constructed, as a function of temperature and drawing ratio (DR) in the range 1.5–4. In the range from DR = 2 to 4 the orientation is clearly uniplanar‐axial. At T_draw = 100°C the crystallinity shown by DSC analysis is higher than the sample stretched at 160°C. The orientation is also higher when samples are stretched at 100°C. The naphthalene rings mainly stay in the plane of the film with a lower fraction perpendicular to the plane of the film. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 103: 395–401, 2007     

Polymer distribution during bicomponent melt blowing of poly(propylene)/poly(ethylene terephthalate) and its improvement

Bicomponent melt blown (MB) microfiber nonwovens of poly(propylene) (PP) and poly(ethylene terephthalate) (PET) were produced in this study. It is interesting to analyze the polymer distribution uniformity across the web because it affects many end‐use properties. By utilizing the technique of differential scanning calorimetry (DSC), a standard working line between heat of fusion and weight percentage was constructed for mixtures of PP and PET components. The fitted equations were used for determination of a component percentage in a certain position across the MB web. Measurements were conducted from DSC re‐heating curves to achieve accurate results. The distribution of polymer varies with polymer mass ratio and processing conditions. The overall uniformity increased with the percentage of PP. When PP is the minor component in the polymer pair, it exhibits notably higher percentage in edge areas across the MB web. These results suggest the phase interface distortion of the polymer melt occurred at the entrance of the MB coat‐hanger die tip. The polymer distribution uniformity is improved by adjusting temperature profile of the MB die. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 85: 2885–2889, 2002     

Use of pyrolyzed oil shale as filler in poly(ethylene‐co‐vinyl acetate) with different vinyl acetate contents

Pyrolyzed oil shale (POS) obtained from the pyrolysis of bituminous rock was used as filler in poly(ethylene‐co‐vinyl acetate) (EVA). The effects of the VA content of EVA and the particle size of POS on the mechanical properties were investigated. The composites were prepared in a rotor mixer at 180°C with a concentration of POS of up to 30 wt %. The stress–strain plots of the compression‐molded composites are similar to the EVA (18% VA content) behavior for low concentrations (1–5 wt %) of POS with a particle size lower than 270 mesh. It was observed that decreasing the POS particle size and increasing the VA content of EVA produced better compatibility between the polymer and filler. The mechanical properties, differential scanning calorimetry, and dynamic mechanical analysis also demonstrated the compatibility between EVA and POS under the increase of the VA content in the EVA. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 84: 1544–1555, 2002; DOI 10.1002/app.10494     

Fabrication,characterization, and properties of poly(ethylene‐co‐vinyl acetate)/magnetite nanocomposites

Poly(ethylene‐co‐vinyl acetate) (EVA)/magnetite (Fe₃O₄) nanocomposite was prepared with different loading of Fe₃O₄ nanoparticles. The mixing and compounding were carried out on a two‐roll mixing mill and the sheets were prepared in a compression‐molding machine. The effect of loading of nanoparticles in EVA was investigated thoroughly by different characterization technique such as transmission electron microscopy (TEM), X‐ray diffraction (XRD), differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), limiting oxygen index (LOI), and technological properties. TEM analysis showed the uniform dispersion of filler in the polymer matrix and the dispersion of filler decreased with increase in filler content. XRD of the nanocomposite revealed the more ordered structure of the polymer chain. An appreciable increase in glass transition temperature was observed owing to the restricted mobility of Fe₃O₄‐filled EVA nanocomposite. TGA and flame resistance studies indicated that the composites attain better thermal and flame resistance than EVA owing to the interaction of filler and polymer segments. Mechanical properties such as tensile strength, tear resistance, and modulus were increased for composites up to 7 phr of filler, which is presumably owing to aggregation of Fe₃O₄ nanoparticle at higher loading. The presence of Fe₃O₄ nanoparticles in the polymer matrix reduced the elongation at break and impact strength while improved hardness of the composite than unfilled EVA. The change in technological properties had been correlated with the variation of polymer–filler interaction estimated from the swelling behavior. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 40116.