The effect of gamma irradiation on mechanical, and thermal properties of recycling polyethylene terephthalate and low density polyethylene (R-PET/LDPE) blend compatibilized by ethylene vinyl acetate (EVA)

A study has been made on the compatibility of recycled polyethylene terephthalate (R-PET) and low density polyethylene (LDPE) blend in the presence of ethylene vinyl acetate (EVA) as a compatibilizing agent prepared by extrusion hot stretching process. EVA content in the blend as a compatibilizing agent was an enhancement effect on radiation crosslinking of R-PET/EVA/LDPE blends and the highest radiation crosslinking was obtained when the EVA content was reached at 10 % EVA when irradiated by gamma irradiation. Blends containing different (EVA) ratios were irradiated to different doses of gamma irradiation 25, 50 and 100 kGy. The effect of the compatibilizer and radiation on mechanical, thermal properties of R-PET together with LDPE and morphology has been investigated. It was found that gamma irradiation together with the presence of compatibilizing agent (EVA) has positive effect on the mechanical and thermal properties of R-PET/LDPE blend. The structural properties of R-PET/LDPE modified by gamma irradiation and EVA as compatibilizing agent was examined by SEM. Also, it was found that the optimum concentration of EVA and gamma irradiation dose was found to be 10 % EVA and 100 kGy, respectively.     

Characterization and properties of polyethylene blends I. Linear low-density polyethylene with high-density polyethylene

A blend system of linear low-density polyethylene (LLDPE) (ethylene butene-1 copolymer) with high-density (linear) polyethylene (HDPE) is investigated by differential scanning calorimetry (DSC), wide-angle x-ray diffraction (WAXD), small-angle x-ray scattering (SAXS), Raman longitudinal-acoustic-mode spectroscopy (LAM), and light scattering (LS). For slowly cooled or quenched samples, one single endotherm is evident in the DSC curve which depends on the composition. No separate peaks are observed in the WAXD, SAXS, Raman-LAM, and LS studies on the LLDPE/HDPE blends. This observation along with the fact that no peak broadening is observed suggests that these peaks are associated with the presence of a single component. In no case did we see double peaks or a broadened peak that might be associated with two closely spaced unresolved peaks. This suggests that segregation has not taken place at the structural levels of crystalline, lamellar, and spherulitic textures. A single-step drop in the scattered intensity (I_Hv) as a function of temperature is seen in the LS studies. It is therefore concluded that cocrystallization between the LLDPE and HDPE components occurs. The mechanical and optical α, β, and γ relaxations of these blends are explored by dynamic birefringence. The 50/50 blend displays the intermediate relaxation behavior between those of the components in all α, β, and γ regions. This observation is reminiscent of the characteristic of the typical miscible blends.     

Reactive Compatibilization of Polyethylene/Ground Tire Rubber Inhomogeneous Blends via Interactions of Pre-Functionalized Polymers in Interface

Summary: Reactive compatibilization of recycled low- or high-density polyethylenes (LDPE and HDPE, respectively) and ground tire rubber (GTR) via chemical interactions of pre-functionalized components in their blend interface has been carried out. Polyethylene component was functionalized with maleic anhydride (MAH) as well as the rubber component was modified via functionalization with MAH or acrylamide (AAm) using chemically or irradiation (γ-rays) induced grafting techniques. The grafting degree and molecular mass distribution of the functionalized polymers have been measured via FTIR and Size Exclusion Chromatography (SEC) analyses, respectively. Thermoplastic elastomer (TPE) materials based on synthesized reactive polyethylenes and GTR as well as ethylene-propylene-diene rubber, EPDM were prepared by dynamic vulcanization of the rubber phase inside thermoplastic (polyethylene) matrix and their phase structure, and main properties have been studied using DSC and mechanical testing. As a final result, the high performance TPE with improved mechanical properties have been developed.     

Thermomechanical study of low-density polyethylene, polyamide 6 and its blends

By using thermomechanical analysis (TMA) multiple relaxation transitions in the amorphous part of semi-crystalline polymers and their blends can be found. These result from differences in the interaction energies between segments of macromolecules, and as a result, in molecular mobility. TMA shows essential changes in the structure of low-density polyethylene (LDPE) resulting from the grafting of a maleic anhydride (LDPE-g-MAH) onto this semi-crystalline polymer. The grafting process did not suppress the ability of polyethylene to crystallize. Essential changes were found in molecular weight distribution and relaxation transitions of the ternary blends LDPE/PA6 (polyamide 6, PA6)/LDPE-g-MAH studied. For a concentration of PA6 up to 30 wt.%, a single relaxation transition is visible, which testifies that the components are miscible in the amorphous region. For blends with 40 and 50 wt.% of PA6, this structure was transformed and two relaxation transitions are visible. From the results obtained in this study it is concluded that the introduction 5 wt.% of grafted polyethylene is sufficient to produce a PA6/LDPE blend only for PA6 concentration up to 30 wt.% which is homogenous on “molecular” level. The transformation of the structure of the ternary polymer blend was explained by the interaction of the components during the melt mixing and changes in the structure of its amorphous regions.     

Characterizing blends of linear low-density and low-density polyethylene by DSC

Summary A two-step isothermal annealing (TSIA) procedure is described that enables the endothermic peaks of low-density polyethylene (LDPE), linear low-density polyethylene (LLDPE) and their blends, to be satisfactorily resolved during analysis by differential scanning calorimetry. A modified form of multistep isothermal annealing, the TSIA procedure produces a highly characteristic profile of the blend components by facilitating the segregation of the phases based on branch density. It is proposed that the TSIA procedure may have significant merit in the identification and quantification of the components in an unknown blend as well as increasing the sensitivity in analytical procedures aimed at blend component quantification.     

Solid-state relaxations in linear low-density (1-octene comonomer), low-density,and high-density polyethylene blends

Extensive thermal and relaxational behavior in the blends of linear low-density polyethylene (LLDPE) (1-octene comonomer) with low-density polyethylene (LDPE) and high-density polyethylene (HDPE) have been investigated to elucidate miscibility and molecular relaxations in the crystalline and amorphous phases by using a differential scanning calorimeter (DSC) and a dynamic mechanical thermal analyzer (DMTA). In the LLDPE/LDPE blends, two distinct endotherms during melting and crystallization by DSC were observed supporting the belief that LLDPE and LDPE exclude one another during crystallization. However, the dynamic mechanical β and γ relaxations of the blends indicate that the two constituents are miscible in the amorphous phase, while LLDPE dominates α relaxation. In the LLDPE/HDPE system, there was a single composition-dependent peak during melting and crystallization, and the heat of fusion varied linearly with composition supporting the incorporation of HDPE into the LLDPE crystals. The dynamic mechanical α, β, and γ relaxations of the blends display an intermediate behavior that indicates miscibility in both the crystalline and amorphous phases. In the LDPE/HDPE blend, the melting or crystallization peaks of LDPE were strongly influenced by HDPE. The behavior of the α relaxation was dominated by HDPE, while those of β and γ relaxations were intermediate of the constituents, which were similar to those of the LLDPE/HDPE blends. © 1997 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 35 : 1633–1642, 1997     

A study on melt grafting of maleic anhydride onto low‐density polyethylene and its blend with polyamide 6

Graft copolymerization of low‐density polyethylene (LDPE) with a maleic anhydride (MAH) was performed using intermeshing corotating twin‐screw extruder in the presence of benzoyl peroxide (BPO). The LDPE/polyamide 6 (PA6) and LDPE‐g‐MAH/PA6 blends were prepared in a corotating twin‐screw extruder. The melt viscosity of the grafted LDPE was measured by a capillary rheometer. The grafted copolymer was characterized by Fourier transform infrared spectroscopy (FTIR) and scanning electron microcopy (SEM). The influence of the variation in temperature, BPO and MAH concentration, and temperature on the grafting degree and on the melt viscosity was studied. The grafting degree increased appreciably up to about 0.45 phr and then decreased continuously with an increasing BPO concentration. According to the FTIR analysis, it was found that the amount of grafted MAH on the LDPE chains was ～5.1%. Thermal analysis showed that melting temperature of the graft copolymers decreases with increasing grafting degree. In addition to this, loss modulus (E″) of the copolymers first increased little with increasing grafting and then obviously decreased with increasing grafting degree. Furthermore, the results revealed that the tensile strength of the blends increased linearly with increasing PA6 content. The results of SEM and mechanical test showed that the blends have good interfacial adhesion and good stability of the phase structure, which is reflected in the mechanical properties. © 2009 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 48: 267–275, 2010     

Compatibilizing effect of isocyanate functional group on polyethylene terephthalate/low density polyethylene blends

To evaluate the compatibilizing effects of isocyanate (NCO) functional group on the polyethylene terephthalate/low density polyethylene (PET/LDPE) blends, LDPE grafted with 2-hydroxyethyl methacrylate-isophorone diisocyanate (LDPE-g-HI) was prepared and blended with PET. The chemical reaction occurred during the melt blending in the PET/LDPE-g-HI blends was confirmed by the result of IR spectra. In the light of the blend morphology, the dispersions of the PET/LDPE-g-HI blends were very fine over the PET/LDPE blends. DSC thermograms indicated that PET microdispersions produced by the slow cooling of the PET/LDPE-g-HI blends were largely amorphous, with low crystallinity, due to the chemical bonding. The tensile strengths of the PET/LDPE-g-HI blends were higher than those of the PET/LDPE blends having a poor adhesion. © 1998 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 36: 447–453, 1998     

Reactive compatibilization of recycled low density polyethylene/butadiene rubber blends during dynamic vulcanization

For reactive compatibilization of the recycled LDPE with butadiene rubber (BR) an equal quantity of few couples of reactive polyethylene copolymer/reactive polybutadiene (1/1) were introduced into the corresponding phases before the dynamic vulcanization. The LDPE/BR thermoplastic dynamic vulcanizates (TDVs) produced using the poly(ethylene-co-acrylic acid), PE-AA/polybutadiene terminated with isocyanate groups, PB-NCO compatibilizing couple with different ratio of functional groups have demonstrated the best mechanical properties and have been characterized by X-Ray analysis and DMTA measurements. For all of systems studied the increasing components compatibility due to the formation of the essential interface layer have been observed. The PB-NCO modifier participates in two processes: it is co-vulcanised with BR in rubber phase and reacts in the interface with the PE-AA dissolved in LDPE. The amorphous phase of LDPE is dissolved by rubber phase, i.e. the morphology with dual phase continuity is formed that provides an improvement of mechanical characteristics of material obtained. The best combination of mechanical characteristics was obtained for LDPE(PE-AA)/BR(PB-NCO), PB-NCO=7.5 wt.% per PB, COOH/NCO=1/1. The tensile strength and an elongation at break for these blends were 3.9 MPa and 353% and for the basic non-compatibilized blend 3.2 MPa and 217%, relatively.     

Effects of different types of polyethylene on the morphology and properties of recycled poly(ethylene terephthalate)/polyethylene compatibilized blends

Recycled poly(ethylene terephthalate) (R‐PET) was blended with four types of polyethylene (PE), linear low density polyethylene (LLDPE; LL0209AA, Fs150), low density polyethylene (LDPE; F101‐1), and metallocene‐LLDPE (m‐LLDPE; Fv203) by co‐rotating twin‐screw extruder. Maleic anhydride‐grafted poly(styrene‐ethylene/butyldiene‐styrene) (SEBS‐g‐MA) was added as compatibilizer. R‐PET/PE/SEBS‐g‐MA blends were examined by scanning electron microscopy (SEM), differential scanning calorimeter (DSC), dynamic mechanical analysis (DMA), and mechanical property testing. The results indicated that the morphology and properties of the blends depended to a great extent on the miscibility between the olefin segments of SEBS‐g‐MA and PE. Due to the proper interaction between SEBS‐g‐MA and LDPE (F101‐1), most SEBS‐g‐MA, located at the interface between two phases of PET and LDPE to increase the interfacial adhesion, lead to better mechanical properties of R‐PET/LDPE (F101‐1) blend. However, both the poor miscibility of SEBS‐g‐MA with LLDPE (LL0209AA) and the excessive miscibility of SEBS‐g‐MA with LLDPE (Fs150) and m‐LLDPE (Fv203) reduced the compatibilization effect of SEBS‐g‐MA. DSC results showed that the interaction between SEBS‐g‐MA and PE obviously affected the crystallization of PET and PE. DMA results indicated that PE had more influence on the movement of SEBS‐g‐MA than PE did. Copyright © 2010 John Wiley & Sons, Ltd.     

Molecular design of multicomponent polymer systems. III. Comparative behavior of pure and tapered block copolymers in emulsification of blends of low-density polyethylene and polystyrene

Poly(hydrogenated butadiene-b-styrene) copolymers are very effective emulsifiers for blends of polystyrene and low-density or high-density polyethylene. It is shown that the extent of improvement in mechanical properties is dependent not only on the molecular weight but also on the structure of the diblock copolymer. A comparative study of the morphology and the mechanical behavior of modified low-density polyethylene/polystyrene blends demonstrates that a tapered diblock is more efficient than a pure diblock with the same composition and molecular weight. It is assumed that the unique behavior of the tapered sample results from its particular miscibility characteristics at the blend interface. The tapered copolymer could behave essentially as a solu-bilizing agent for the homopolymers at the interface and provide a “graded” modulus responsible for the improved mechanical response of the material.     

Characterization and properties of polyethylene blends II. Linear low-density with conventional low-density polyethylene

Melting and crystallization phenomena in blends of a linear low-density polyethylene (LLDPE) (ethylene butene-1 copolymer) with a conventional low-density (branched) polyethylene (LDPE) are explored with emphasis on composition by differential scanning calorimetry (DSC) and light scattering (LS). Two endotherms are evident in the DSC studies of the blends, which suggests the formation of separate crystals. Light-scattering studies indicate that the blend system is predominantly volume filled by the LLDPE component whereby the LDPE component crystallizes as a secondary process within the domain of the LLDPE spherulites. In contrast to those of the LLDPE/HDPE blends, the mechanical and optical relaxation behavior of the LLDPE/LDPE blends are dominated by the LLDPE component in the vicinities of γ and β regions, whereas the trend reverses at high temperature α regions. This observation is accounted for on the basis of the relative restrictions imposed by the deformation of spherulites (which are primarily made up of the LLDPE component) at different time scales.     

Photo-oxidation behaviour of polyethylene/polyamide 6 blends filled with organomodified clay: Improvement of the photo-resistance through morphology modification

The impact of small amounts of organomodified clay (OMMT) on the photo-degradation behaviour of two blends obtained by mixing either low-density polyethylene (LDPE) or high density polyethylene (HDPE) with polyamide 6 (PA6) (LDPE/PA6 and HDPE/PA6 75/25 wt-%) was studied. The complex photo-degradation behaviour was followed by monitoring the main physical-mechanical properties of the blends. In particular, mechanical and spectroscopic tests were performed in conditions of accelerated artificial aging. An accurate mechanical and morphological characterization was previously carried out. The presence of the OMMT promotes the unexpected formation of a co-continuous morphology for the HDPE/PA6 blend without significantly improving the interfacial adhesion. Differently, the OMMT-filled LDPE/PA6 blend exhibits a finely distributed morphology, and some apparent improvement of the interfacial adhesion was noticed. Probably due to these differences in microstructure, a different impact of the nanoparticles on the photo-resistance behaviours was observed for the two families of samples. In particular, the HDPE-based nanocomposite blend exhibits an improved photo-resistance, while the opposite occurs for the LDPE-based system.     

Stress–strain behavior of low‐density polyethylene/poly(methyl methacrylate) blends with modulated interfaces with a hydrogenated polybutadiene‐block‐poly(methyl methacrylate) diblock copolymer

The stress–strain diagrams and ultimate tensile properties of uncompatibilized and compatibilized hydrogenated polybutadiene‐block‐poly(methyl methacrylate) (HPB‐b‐PMMA) blends with 20 wt % poly(methyl methacrylate) (PMMA) droplets dispersed in a low‐density polyethylene (LDPE) matrix were studied. The HPB‐b‐PMMA pure diblock copolymer was prepared via controlled living anionic polymerization. Four copolymers, in terms of the molecular weights of the hydrogenated polybutadiene (HPB) and PMMA sequences (22,000–12,000, 63,300–31,700, 49,500–53,500, and 27,700–67,800), were used. We demonstrated with the stress–strain diagrams, in combination with scanning electron microscopy observations of deformed specimens, that the interfacial adhesion had a predominant role in determining the mechanism and extent of blend deformation. The debonding of PMMA particles from the LDPE matrix was clearly observed in the compatibilized blends in which the copolymer was not efficiently located at the interface. The best HPB‐b‐PMMA copolymer, resulting in the maximum improvement of the tensile properties of the compatibilized blend, had a PMMA sequence that was approximately half that of the HPB block. Because of the much higher interactions encountered in the PMMA phase in comparison with those in HPB (LDPE), a shorter sequence of PMMA (with respect to HPB but longer than the critical molecular weight for entanglement) was sufficient to favor a quantitative location of the copolymer at the LDPE/PMMA interface. © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 43: 22–34, 2005     

Space charge distribution and crystalline structure in polyethylene blended with EVOH

The space charge distribution in polyethylene samples under direct current (DC) electrical field was measured by pulsed electro-acoustic (PEA) method. It was found that by blending with 5 wt.% of poly(ethylene-co-vinyl alcohol) (EVOH) in low-density polyethylene (LDPE) the amount of accumulated space charges decreased and the field distribution of space charge improved. The differential scanning calorimetry (DSC) study showed that crystallization of LDPE/EVOH started at a higher temperature than LDPE. The results of wide-angle X-ray diffraction (WAXD) and small-angle light scattering (SALS) for LDPE/EVOH indicated that the crystal forms did not change, whereas the spherulites became smaller and imperfective. It can be seen from the results that EVOH played a role of nucleation during the crystallization of LDPE in the blend. The observation of scanning electron microscope (SEM) showed that the domains of EVOH were dispersed in LDPE as particles in diameter of 1 μm. The reduction of space charges in the blend sample can be explained as the results of the trapping of homo-charges at the interface and the dissipation of charges through LDPE matrix consisting of smaller spherulites.     

Sugar end-capped polyethylene: Ceric ammonium nitrate initiated oxidation and melt phase grafting of glucose onto polyethylene and its microbial degradation

Low density polyethylene (LDPE) was modified to introduce biodegradability by grafting highly hydrophilic monomers (which can act as nutrients for microorganisms) such as glucose by a novel melt phase reaction using Brabender plasti-corder in the presence of ceric ammonium nitrate (CAN) to obtain 4-O-hydroxymethyl d-arabinose (sugar) end-capped LDPE (Su-g-LDPE) at a maximum grafting of 16%. The grafted polymers were characterized by FTIR, thermal analysis, WAXD and mechanical property measurements. The biodegradability of Su-g-LDPE was carried out by soil-burial test and by optical density measurements in presence of an aerobic bacterium Pseudomonas sp. The degraded polymer shows changes in weight, crystallinity and inherent viscosity. Optical density of the medium registered an increase with degradation. FTIR spectra of the degraded samples showed 70% decrease in the ketone carbonyl index (ν₁₇₁₉/ν₁₄₆₅) of Su-g-LDPE indicating microbial degradation of LDPE matrix, which was further confirmed by SEM micrographs. The present data support a microbial oxidation process involving β-oxidation whereby the carbonyl is further oxidized to carboxylic acid and affects cleavage of the LDPE chain at the ends.     

Additive‐like amounts of HDPE prevent creep of molten LDPE: Phase‐behavior and thermo‐mechanical properties of a melt‐miscible blend

Low‐density polyethylene (LDPE) is the preferred type of polyolefin for many medical and electrical applications because of its superior purity and cleanliness. However, the inferior thermo‐mechanical properties as compared to, for example, high‐density polyethylene (HDPE), which arise because of the lower melting temperature of LDPE, constitute a significant drawback. Here, we demonstrate that the addition of minute amounts of HDPE to a LDPE resin considerably improves the mechanical integrity above the melting temperature of LDPE. A combination of dynamic mechanical analysis and creep experiments reveals that the addition of as little as 1 to 2 wt% HDPE leads to complete form stability above the melting temperature of LDPE. The investigated LDPE/HDPE blend is found to be miscible in the melt, which facilitates the formation of a solid‐state microstructure that features a fine distribution of HDPE‐rich lamellae. The absence of creep above the melting temperature of LDPE is rationalized with the presence of tie chains and trapped entanglements that connect the few remaining crystallites. © 2016 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2017 , 55, 146–156     

Study on rheological properties and relaxational behavior of poly(dianilinephosphazene)/low-density polyethylene blends

Rheological properties and relaxational behavior of blends of low-density polyethylene (LDPE) and poly(dianilinephosphazene) (PDAP) have been investigated to check miscibility and molecular relaxations in the crystalline and amorphous phases. In the studied shear rate range, all PDAP/LDPE blends exhibited a shear thinning behavior. The experimental data were fitted using the logarithmic rule and serial model to investigate the miscibility of blends. It was found that LDPE and PDAP can achieve a certain degree of miscibility in the molten state. The dynamic mechanical α-, β- and γ-relaxation behavior obtained from dynamic mechanical thermal analysis imply that the two components in the amorphous phase were miscible. The wide-angle X-ray diffraction result showed that these two components interact with each other.     

Effect of cobalt carboxylates on the photo-oxidative degradation of low-density polyethylene. Part-I

The effect of three cobalt carboxylates of increasing chain length, namely cobalt laurate, cobalt palmitate and cobalt stearate on the photo-oxidative degradation of low-density polyethylene (LDPE) films has been investigated. LDPE films containing cobalt carboxylates were irradiated with UV-B light at 30 °C for extended time periods. FTIR spectroscopy, mechanical testing, morphological studies, molecular weight, density and MFI measurements were performed to monitor the degradation behaviour. The results of these studies were analysed to explain the structural and chemical modifications taking place in the polyethylene matrix due to UV-B exposure. FTIR studies indicate that the degradation is dominated by formation of carbonyl and vinyl species. The studies on mechanical properties reveal that samples containing cobalt carboxylates, become mechanically fragile after UV exposure for 400 h, while neat LDPE exhibits insignificant changes during this period. The degradation was found to increase proportionally with increasing chain length and follows the order CoSt₃ > CoPal₃ > CoLau₃. Migration studies were performed on food simulant systems to investigate the applicability of these films for food packaging.     

Thermooxidative degradation of polyethylene. I and II. Structural changes occurring in low-density polyethylene,high-density polyethylene,and tetratetracontane heated in air

Samples of low-density polyethylene (LDPE), high-density polyethylene (HDPE), and tetratetracontane (n-C₄₄H₉₀) free from additives were heated in air at temperatures between 120 and 180°C. As a comparison, “as received” HDPE containing unspecified additives has also been included. The structural changes have been studied with gel chromatography, viscometry, infrared spectroscopy, differential scanning calorimetry, and gravimetric measurements. LDPE, HDPE, and n-C₄₄H₉₀ follow the same course of thermooxidative degradation when they are free from additives and present in the molten state. Both molecular-diminishing and enlargement reactions occur. At temperatures below 150°C molecular enlargement is not observed until after rather long exposure times, whereas at higher temperatures enlargement occurs immediately. The difference is because “peroxide curing” becomes increasingly important above 150°C, whereas ester formation is operating at all temperature levels. Degradation below T_m is restricted to the amorphous phase that results in a different degradation pattern. In accelerated testing work extrapolations of the Arrhenius type in the prediction of structural change are thus not justified, even within the actual narrow temperature range. Neither are changes in commonly used standards like carbonyl content justified as a measure of the changes; for example, in mechanical properties. The stabilizer in the unpurified HDPE not only influences the induction period but also the course of the thermooxidative degradation.