Effect of confinement on glass dynamics and free volume in immiscible polystyrene/high‐density polyethylene blends

The effect of confinement on glass dynamics combined with the corresponding free volume changes of amorphous polystyrene (PS) in blends with semi‐crystalline high‐density polyethylene (HDPE) have been investigated using thermal analyses and positron annihilation lifetime spectroscopy (PALS). Two different glass transition temperatures (T_g) were observed in a PS/HDPE blend due to the dissimilarity in the chemical structure, consistent with an immiscible blend. However, T_g of PS in the incompatible PS/HDPE blend showed an upward trend with increasing PS content resulting from the confinement effect, while T_g of the semi‐crystalline HDPE component became lower than that of neat HDPE. Moreover, the elevation of T_g of PS was enhanced with a decrease of free volume radius by comparing annealed and unannealed PS/HDPE blends. Positron results showed that the free volume radius clearly decreased with annealing for all compositions, although the free volume hole size agreed well with linear additivity, indicating that there was only a weak interaction between the two components. Combining PALS with thermal analysis results, the confinement effect on the glass dynamics and free volume of PS phase in PS/HDPE blends could be attributed to the shrinkage of HDPE during crystallization when HDPE acted as the continuous phase. © 2015 Society of Chemical Industry     

Effect of silane grafting on the microstructure of high‐density polyethylene/organically modified montmorillonite nanocomposites

Organically modified montmorillonite (org‐MMT) and high‐density polyethylene (HDPE) grafted with silane groups (HDPE‐g‐silane) were melt compounded to give HDPE‐g‐silane‐blend‐org‐MMT nanocomposites. X‐ray diffractometry was performed to investigate the intercalation effect. Transmission electron microscopy was applied to observe the dispersion of org‐MMT layers in HDPE matrices. The results indicate that an intercalated structure can be easily obtained in HDPE‐g‐silane‐blend‐org‐MMT nanocomposites. Furthermore, positron annihilation lifetime spectroscopy was used to characterize the microstructure of the composites. It is found that the ortho‐positron (o‐Ps) intensity for HDPE‐g‐silane is decreased by approximately 10% with a narrower lifetime distribution than that for HDPE. With increasing org‐MMT concentration, the o‐Ps intensity I₃ increases for HDPE‐g‐silane‐blend‐org‐MMT nanocomposites; however, for HDPE‐blend‐org‐MMT composites I₃ decreases. It is found that HDPE composites with good dispersion can be obtained following appropriate modification of the HDPE. And silane grafting has an effect on the free volume of the HDPE nanocomposites. Copyright © 2007 Society of Chemical Industry     

Thermal properties and morphology of noncrosslinking linear low‐density polyethylene‐grafted acrylic acid

Noncrosslinking linear low‐density polyethylene‐grafted acrylic acid (LLDPE‐g‐AA) was prepared by melt‐reactive extrusion in our laboratory. The thermal behavior of LLDPE‐g‐AA was investigated by using differential scanning calorimetry (DSC). Compared with neat linear low‐density polyethylene (LLDPE), melting temperature (T_m) of LLDPE‐g‐AA increased a little, the crystallization temperature (T_c) increased about 4°C, and the melting enthalpy (ΔH_m) decreased with an increase in acrylic acid content. Isothermal crystallization kinetics of LLDPE and LLDPE‐g‐AA samples were carried out by using DSC. The overall crystallization rate of LLDPE was smaller than that of grafted samples. It showed that the grafted acrylic acid monomer onto LLDPE acted as a nucleating agent. Crystal morphologies of LLDPE‐g‐AA and LLDPE were examined by using SEM. Spherulite sizes of LLDPE‐g‐AA samples were lower than that of LLDPE. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 86: 2626–2630, 2002     

Synthesis functional poly(carbonate‐b‐ester) copolymers and micellar characterizations

Functional poly(carbonate‐b‐ester)s were synthesized in buck by ring‐opening polymerization of the carbonate (TMC, MBC, or BMC) with tert‐butyl N‐(2‐hydroxyethyl) carbamate as an initiator, and then with ε‐CL (or ε‐BCL) comonomer. Subsequently, the PMMC‐b‐PCL with pendent carboxyl groups and the PTMC‐b‐PHCL with pendent hydroxyl groups were obtained by catalytic debenzylation. DSC analysis indicated that only one T_g at an intermediate temperature the T_gs of the two polymer blocks. A decrease T_g was observed when an increase contents of ε‐CL incorporated into the copolymers. In contrast, two increased T_ms were observed with increasing PCL content. The block copolymers formed micelle in aqueous phase with critical micelle concentrations (cmcs) in the range of 2.23–14.6 mg/L and with the mean hydrodynamic diameters in the range of 100–280 nm, depending on the composition of copolymers. The drug entrapment efficiency and hydrolytic degradation behavior of micelle were also evaluated. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2007     

Quantitative analysis of cloisite 93A infused into linear low‐density polyethylene and maleated linear low‐density polyethylene in a supercritical carbon dioxide medium

Linear low‐density polyethylene (LLDPE) is a widely used polymer that can benefit from the enhanced barrier, thermal, and mechanical properties offered by nanoclay fillers. However, optimal property enhancement requires complete exfoliation and uniform dispersion, both of which are difficult to achieve with nanoclay fillers. Supercritical carbon dioxide (scCO₂) processing is an inexpensive and environmentally benign method for exfoliating and dispersing clays into polymers. In a scCO₂ medium under controlled environments, the organically modified clay Cloisite 93A was infused into LLDPE and maleated linear low‐density polyethylene (LLDPE‐g‐MA). Upon microscopic inspection, it was evident that clay infusion was achieved near the surface of the polymer pellet, but no clay found its way into the interior of the pellet. In this article, we describe an analytical method for determining the amount of nanoclay infused into a polymer matrix via Fourier transform infrared analysis. Using this method, we determined the weight percentage of Cloisite 93A infused into LLDPE and LLDPE‐g‐MA. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

Variations of the glass‐transition temperature in the imidization of poly(styrene‐co‐maleic anhydride)

The imidization of poly(styrene‐co‐maleic anhydride) (SMA) was conducted, and the glass‐transition temperatures (T_g's) of the resulting products were measured with differential scanning calorimetry. The contributions from functional groups of maleic anhydride, N‐phenylmaleamic acid, and N‐phenylmaleimide to T_g were examined. T_g increased in the order of SMA < styrene–N‐phenyl maleimide copolymer < styrene–N‐phenyl maleamic acid copolymer and followed the Fox equation. T_g of the imidized products of SMA could be controlled by the conversions of both ring‐opening and ring‐closing reactions. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 104: 2418–2422, 2007     

Property transitions in high‐density polyethylene/maleated poly(ethylene–octene)/calcium carbonate ternary composites

Ternary composites of high‐density polyethylene (HDPE)/maleated poly(ethylene–octene) (POE‐g)/calcium carbonate (CaCO₃) were prepared by the melt extrusion process. Crystallization behavior investigation and mechanical properties study showed that there existed a transition in both crystallization temperature (T_c) and impact strength of ternary composites. These transitions were attributed to the development of morphology, with variation of concentration of POE‐g in ternary composites. The strength of interfacial adhesion also influenced the property transitions. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 101: 3361–3366, 2006     

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

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

Functionalization of high‐density polyethylene in the molten state by glycidyl methacrylate grafting

:This study concerns the melt‐free radical grafting of glycidyl methacrylate (GMA) onto high‐density polyethylene (HDPE). We studied the effect of two initiators (tert‐butyl cumyl peroxide and di‐tert‐butyl peroxide) onto HDPE. Crosslinking of polymer was observed in the presence of 0.3 wt % tert‐butyl cumyl peroxide but not with 0.3 wt % di‐tert‐butyl peroxide. The grafting was carried out in a Brabender batch mixer at 190 °C. The grafting yield of GMA onto HDPE (determined by infrared spectrometry) is weak (<1 wt % for an initial concentration in monomer of 6 wt %). Moreover, it was noted that the degree of grafting did not vary with the concentration and the nature of peroxide used. To increase the grafting yield of GMA, we added to the HDPE/peroxide/GMA system an electron‐donating monomer, such as styrene. Adding this comonomer multiplied the rate of grafted GMA 3‐ or 4‐fold, resulting in a ratio [styrene]_i/[GMA]_i = 1 mol/mol with [GMA]_i = 6 wt %. So, the copolymerization is favored compared with the homopolymerization. This kind of copolymer presenting reactive functions is very attractive in the field of compatibilizing immiscible polymers. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 81: 581–590, 2001     

Toughened polyoxymethylene by polyolefin elastomer and glycidyl methacrylate grafted high‐density polyethylene

Ternary blends of polyoxymethylene (POM), polyolefin elastomer (POE), and glycidyl methacrylate grafted high density polyethylene (GMA‐g‐HDPE) with various component ratios were studied for their mechanical and thermal properties. The size of POE dispersed phase increased with increasing the elastomer content due to the observed agglomeration. The notched impact strength demonstrated a parabolic tendency with increasing the elastomer content and reached the peak value of 10.81 kJ/m² when the elastomer addition was 7.5 wt%. The disappearance of epoxy functional groups in the POM/POE/GMA‐g‐HDPE blends indicated that GMA‐g‐HDPE reacted with the terminal hydroxyl groups of POM and formed a new graft copolymer. Higher thermal stability was observed in the modified POM. Both storage modulus and loss modulus decreased from dynamic mechanical analysis tests while the loss factor increased with increasing the elastomer content. GMA‐g‐HDPE showed good compatibility between the POM matrix and the POE dispersed phase due to the reactive compatibilization of the epoxy groups of GMA and the terminal hydroxyl groups of POM. A POM/POE blend without compatibilizer was researched for comparison, it was found that the properties of P‐7.5(POM/POE 92.5 wt%/7.5 wt%) were worse than those of the blend with the GMA‐g‐HDPE compatibilizer. POLYM. ENG. SCI., 57:1119–1126, 2017. © 2017 Society of Plastics Engineers     

Phase structure and properties of poly(ethylene terephthalate)/high‐density polyethylene based on recycled materials

Blends based on recycled high density polyethylene (R‐HDPE) and recycled poly(ethylene terephthalate) (R‐PET) were made through reactive extrusion. The effects of maleated polyethylene (PE‐g‐MA), triblock copolymer of styrene and ethylene/butylene (SEBS), and 4,4′‐methylenedi(phenyl isocyanate) (MDI) on blend properties were studied. The 2% PE‐g‐MA improved the compatibility of R‐HDPE and R‐PET in all blends toughened by SEBS. For the R‐HDPE/R‐PET (70/30 w/w) blend toughened by SEBS, the dispersed PET domain size was significantly reduced with use of 2% PE‐g‐MA, and the impact strength of the resultant blend doubled. For blends with R‐PET matrix, all strengths were improved by adding MDI through extending the PET molecular chains. The crystalline behaviors of R‐HDPE and R‐PET in one‐phase rich systems influenced each other. The addition of PE‐g‐MA and SEBS consistently reduced the crystalline level (χ_c) of either the R‐PET or the R‐HDPE phase and lowered the crystallization peak temperature (T_c) of R‐PET. Further addition of MDI did not influence R‐HDPE crystallization behavior but lowered the χ_c of R‐PET in R‐PET rich blends. The thermal stability of R‐HDPE/R‐PET 70/30 and 50/50 (w/w) blends were improved by chain‐extension when 0.5% MDI was added. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Polystyrene composites of single‐walled carbon nanotubes‐graft‐polystyrene

Single‐walled carbon nanotubes (SWCNTs) dispersed in N‐methylpyrrolidone (NMP) were functionalized by addition of polystyryl radicals from 2,2,6,6‐tetramethyl‐1‐piperidinyloxy‐ended polystyrene (SWCNT‐g‐PS). The amount of polystyrene grafted to the nanotubes was in the range 20‐25 wt% irrespective of polystyrene number‐average molecular weight ranging from 2270 to 49 500 g mol^?1. In Raman spectra the ratios of D‐band to G‐band intensity were similar for all of the polystyrene‐grafted samples and for the starting SWCNTs. Numerous near‐infrared electronic transitions of the SWCNTs were retained after polymer grafting. Transmission electron microscopy images showed bundles of SWCNT‐g‐PS of various diameters with some of the polystyrene clumped on the bundle surfaces. Composites of SWCNT‐g‐PS in a commercial‐grade polystyrene were prepared by precipitation of mixtures of the components from NMP into water, i.e. the coagulation method of preparation. Electrical conductivities of the composites were about 10^?15 S cm^?1 and showed no percolation threshold with increasing SWCNT content. The glass transition temperature (T_g) of the composites increased at low filler loadings and remained constant with further nanotube addition irrespective of the length and number of grafted polystyrene chains. The change of heat capacity (ΔC_p) at T_g decreased with increasing amount of SWCNT‐g‐PS of 2850 g mol^?1, but ΔC_p changed very little with the amount of SWCNT‐g‐PS of higher molecular weight. The expected monotonic decrease in ΔC_p coupled with the plateau behavior of T_g suggests there is a limit to the amount that T_g of the matrix polymer can increase with increasing amount of nanotube filler. Copyright © 2012 Society of Chemical Industry     

Crystallization behavior of glass bead‐filled low‐density polyethylene composites

The effects of the filler content and the filler size on the crystallization and melting behavior of glass bead‐filled low‐density polyethylene (LDPE) composites have been studied by means of a differential scanning calorimeter (DSC). It is found that the values of melting enthalpy (ΔH_c) and degree of crystallinity (x_c) of the composites increase nonlinearly with increasing the volume fraction of glass beads, ϕ_f, when ϕ_f is greater than 5%; the crystallization temperatures (T_c) and the melting temperatures (T_m) of the composites are slightly higher than those of the pure LDPE; the effects of glass bead size on x_c, T_c, and T_m are insignificant at lower filler content; but the x_c for the LDPE filled with smaller glass beads is obviously greater than that of the filled system with bigger ones at higher ϕ_f. It suggests that small particles are more beneficial to increase in crystallinity of the composites than big ones, especially at higher filler content. In addition, the influence of the filler surface pretreated with a silane coupling agent on the crystallization behavior are not too outstanding at lower inclusion concentration. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 71: 687–692, 1999     

Effect of glass transition temperature and saturation temperature on the solid‐state microcellular foaming of cyclic olefin copolymer

Effect of glass transition temperature and saturation temperature on the solid‐state microcellular foaming of cyclic olefin copolymer (COC)—including CO₂ solubility, diffusivity, cell nucleation, and foam morphology—were investigated in this article. COCs of low T_g (78°C) and high T_g (158°C) were studied. Solubilities are 20–50% higher in high T_g COC than in the low T_g COC across the saturation temperature range. Diffusivities are about 15% higher on average in high T_g COC for temperatures up to 50°C. A much faster increase of diffusivity beyond 50°C is observed in low T_g COC due to it being in the rubbery state. Under similar gas concentration, high T_g COC starts foaming at a higher temperature. And the foam density decreases faster in low T_g COC with foaming temperature. Also, high T_g COC foams show about two orders of magnitude higher cell nucleation density than the low T_g COC foams. The effect of saturation temperature on microcellular foaming can be viewed as the effect of CO₂ concentration. Nucleation density increases and cell size decreases exponentially with increasing CO₂ concentration. Uniform ultramicrocellular structure with an average cell size of 380 nm was created in high‐T_g COC. A novel hierarchical structure composed of microcells (2.5 μm) and nanocells (cell size 80 nm) on the cell wall was discovered in the very low‐density high‐T_g COC foams. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 42226.     

Studies on preparation and properties of vinyltriethoxysilane‐grafted styrene‐butadiene rubber

Graft polymerization of vinyltriethoxysilane (VTES) onto styrene‐butadiene rubber (SBR) was carried out in latex using benzoic peroxide (BPO) as an initiator. The concentration of VTES effecting on vulcanization characteristics, mechanical properties and thermal properties of VTES‐grafted SBR (SBR‐g‐VTES) were investigated. The grafting of VTES onto SBR and its pre‐crosslinking were confirmed by attenuated total teflectance‐Fourier transform infrared reflectance and proton nuclear magnetic resonance. The mechanism of graft polymerization was studied. The results revealed that the minimum torque, optimum cure time, tensile strength, thermal decomposition temperature, and glass transition temperature (T_g) all increased with the increasing concentration of VTES. But the grafting efficiency of VTES, rate of vulcanization, and elongation at break of the SBR‐g‐VTES decreased. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Photobiodegradation of low‐density polyethylene/banana starch films

The effects of the starch content, photosensitizer content, and compatibilizer on the photobiodegradability of low‐density polyethylene (LDPE) and banana starch polymer blend films were investigated. The compatibilizer and photosensitizer used in the films were PE‐graft‐maleic anhydride (PE‐g‐MA) and benzophenone, respectively. Dried banana starch at 0–20% (w/w) of LDPE, benzophenone at 0–1% (w/w) of LDPE, and PE‐g‐MA at 10% (w/w) of banana starch were added to LDPE. The photodegradation of the blend films was performed with outdoor exposure. The progress of the photodegradation was followed by determining the carbonyl index derived from Fourier transform IR measurements and the changes in tensile properties. Biodegradation of the blend films was investigated by a soil burial test. The biodegradation process was followed by measuring the changes in the physical appearance, weight loss, and tensile properties of the films. The results showed that both photo‐ and biodegradation rates increased with increasing amounts of banana starch, whereas the tensile properties of the films decreased. The blends with higher amounts of benzophenone showed higher rates of photodegradation, although their biodegradation rates were reduced with an increase in benzophenone content. The addition of PE‐g‐MA into polymer blends led to an increase in the tensile properties whereas the photobiodegradation was slightly decreased compared to the films without PE‐g‐MA. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 100: 2725–2736, 2006     

Structure and properties of composites of polyethylene or maleated polyethylene and cellulose or cellulose esters

Composites of linear low‐density poly(ethylene‐co‐butene) (PE) or maleated linear low‐density poly (ethylene‐co‐butene) (M‐PE) and cellulose (CEL), cellulose acetate (CA), cellulose acetate propionate (CAP), or cellulose acetate butyrate (CAB) were prepared in an internal laboratory mixer with 20 wt % polysaccharide. The structure and properties of the composites were studied with tensile testing, dynamic mechanical thermal analysis, differential scanning calorimetry, extraction with a selective solvent, Raman spectroscopy, and X‐ray diffraction. Composites prepared with M‐PE presented yield stress and elongation values higher than those of composites prepared with PE, showing the compatibilizer effect of maleic anhydride. Dynamic mechanical thermal analysis performed for M‐PE–CEL, M‐PE–CA, M‐PE–CAP, and M‐PE–CAB composites showed one glass‐transition temperature (T_g) close to that observed for pure M‐PE, and for M‐PE–CAP, another T_g lower than that measured for the polysaccharide was observed, indicating partial mutual solubility. These findings were confirmed by the extraction of one phase with a selective solvent, gravimetry, and Raman spectroscopy. X‐ray diffraction showed that the addition of CEL, CA, CAP, or CAB had no influence on the lattice constants of PE or M‐PE, but the introduction of the reinforcing material increased the amorphous region. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 103:402–411, 2007     

Nonisothermal crystallization kinetics of linear bimodal–polyethylene (LBPE) and LBPE/low‐density polyethylene blends

Nonisothermal crystallization kinetics of linear bimodal–polyethylene (LBPE) and the blends of LBPE/low‐density polyethylene (LDPE) were studied using DSC at various scanning rates. The Avrami analysis modified by Jeziorny and a method developed by Mo were employed to describe the nonisothermal crystallization process of LBPE and LBPE/LDPE blends. The theory of Ozawa was also used to analyze the LBPE DSC data. Kinetic parameters such as, for example, the Avrami exponent (n), the kinetic crystallization rate constant (Z_c), the crystallization peak temperature (T_p), and the half‐time of crystallization (t_1/2) were determined at various scanning rates. The appearance of double melting peaks and double crystallization peaks in the heating and cooling DSC curves of LBPE/LDPE blends indicated that LBPE and LDPE could crystallize, respectively. As a result of these studies, the Z_c of LBPE increases with the increase of cooling rates and the T_p of LBPE for LBPE/LDPE blends first increases with increasing LBPE content in the blends and reaches its maximum, then decreases as the LBPE content further increases. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 89: 2431–2437, 2003     

Graft copolymerization of oleic acid onto low‐density polyethylene in the molten state

A graft copolymer of oleic acid (OA) onto low‐density polyethylene (LDPE) was prepared using dicumyl peroxide (DCP) as an initiator in the molten state. The grafting was carried out in a Haake rheometer. The effects of the reaction time and the amount of DCP and the monomer on the percentage of grafting were studied. The rheological behavior and the melt‐flow rate of the graft copolymer (LDPE‐g‐OA) were also investigated. FTIR spectroscopy and a mass spectrum were used to characterize the structure of LDPE‐g‐OA. The experimental results showed that when the OA amount was 10 wt % and the DCP amount was 0.4 wt % based on the LDPE the percentage of grafting of LDPE‐g‐OA, prepared by maintaining the temperature at 170°C and the roller speed at 80 rpm, was about 6 wt %. It was found that both LDPE and LDPE‐g‐OA were pseudoplastic fluids. OA was grafted onto LDPE in the form of a monomer and a dimer. The grafted LDPE is expected to act as a compatibilizer between starch and polyethylene. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 90: 3299–3304, 2003     

Phase behavior,density, and crystallization of polyethylene in n‐pentane and in n‐pentane/CO2 at high pressures

The phase behavior and volumetric properties of polyethylene (PE) in solutions of n‐pentane and n‐pentane/CO₂ were studied in a temperature (T) range of 370–440 K at pressures up to 60 MPa. Measurements were conducted with a variable‐volume view‐cell system equipped with optical sensors to monitor the changes in the transmitted light intensity as the P or the T of the system was changed. Lower‐critical‐solution‐temperature‐type behavior was observed for all of the liquid–liquid (L–L) phase boundaries, which shifted to higher pressures in solutions containing CO₂. The solid–fluid (S–F) phase boundaries were investigated over a P range of 8–54 MPa and took place in a narrow T range, from 374 to 378 K in this P interval. The S–F phase boundary showed a unique feature in that the demixing temperatures showed both increasing and decreasing trends with P depending on the P range. This was observed in both the PE/n‐pentane and PE/n‐pentane/CO₂ mixtures. The density of these solutions were measured as a function of P at selected temperatures or as a function of T at selected pressures that corresponded to the paths followed in approaching the phase boundaries (S–F or L–L) starting from a homogeneous one‐phase condition. The data showed a smooth variation of the overall mixture density along these paths. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 89: 2201–2209, 2003