Optical properties of injection‐molded polystyrene scintillators. II. Distribution of dopants

The distribution of fluorescing dye solutes in scintillating tiles for the Tilecal/Atlas project is assessed, and a link between the homogeneity of the dopant distribution and the optical yield and nonuniformity is established. The effect of the injection‐molding parameters on the dye distribution is also analyzed, as well as the actual dye incorporation into the scintillators. This incorporation has been assessed with a set of experiments performed with laboratory samples with controlled amounts of additives and with samples obtained from injection‐molded scintillators. Differential scanning calorimetry has been used to characterize the raw material and to establish a link between the thermophysical properties and the processing conditions, and it is proven to be a quite appropriate technique. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 88: 2714–2718, 2003     

Cold‐crystallization kinetics of syndiotactic polystyrene

The kinetics of the isothermal and nonisothermal cold crystallization of syndiotactic polystyrene (s‐PS) were characterized with differential scanning calorimetry. A Johnson–Mehl–Avrami analysis of the isothermal experiments indicated that the cold crystallization of s‐PS at a constant temperature followed a diffusion‐controlled growth mode with a decreasing nucleation rate. Furthermore, the slow nucleation rate was the controlling step of the entire kinetic process. For nonisothermal cold‐crystallization kinetics, we used a simple model based on a combination of the well‐known Avrami and Ozawa models. The analysis revealed that, unlike for melt crystallization, the Avrami and Ozawa exponents were not equal. The activation energies for the isothermal and nonisothermal cold crystallizations of s‐PS were 792.0 and 148.62 kJ mol^?1, respectively, indicating that the smaller motion units in cold crystallization had a weaker temperature dependence than those in melt crystallization. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 89: 3464–3470, 2003     

Degradation behaviors of linear low‐density polyethylene and poly(L‐lactic acid) blends

In this study, the degradability of linear low‐density polyethylene (LLDPE) and poly(L ‐lactic acid) (PLLA) blend films under controlled composting conditions was investigated according to modified ASTM D 5338 (2003). Differential scanning calorimetry, X‐ray diffraction, and Fourier transform infrared spectroscopy were used to determine the thermal and morphological properties of the plastic films. LLDPE 80 (80 wt % LLDPE and 20 wt % PLLA) degraded faster than grafted low‐density polyethylene–maleic anhydride (M‐g‐L) 80/4 (80 wt % LLDPE, 20 wt % PLLA, and 4 phr compatibilizer) and pure LLDPE (LLDPE 100). The mechanical properties and weight changes were determined after composting. The tensile strength of LLDPE 100, LLDPE 80, and M‐g‐L 80/4 decreased by 20, 54, and 35%, respectively. The films, as a result of degradation, exhibited a decrease in their mass. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

Thermally induced microstructural changes and its influence on electrical conductivity of a polymer‐based bakelite RPC detector material: A positron lifetime study

Annealing studies have been carried out to understand the temperature induced microstructural changes in Bakelite (P‐120 NEMA LI‐1989 Grade XXX) Resistive Plate Chamber (RPC) detector material using Positron annihilation lifetime spectroscopy (PALS), Fourier transform infrared spectroscopy (FTIR), and XRD. The variation of positron lifetime parameters viz., ortho‐Positronium lifetime (τ₃) and free volume size (V_f) increases marginally above glass transition temperature T_g as a result of structural changes due to segmental mobility. The drastic increase of free volume parameters above 240°C attributed to the reduction in strength of C—H bond of the aliphatic bridges and cleavage of methylene bridges of the polymer network, which is supported by the FTIR results. The XRD results show the reduction in crystallinity and average crystallite size of Bakelite on annealing correlates well with the free volume and electrical conductivity. The temperature induced electrical conductivity and activation energy is also correlated with the positron lifetime parameters. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 130: 793‐800, 2013     

Isothermal and nonisothermal melt‐crystallization kinetics of syndiotactic polystyrene

Analyses of the isothermal and nonisothermal melt kinetics for syndiotactic polystyrene have been performed with differential scanning calorimetry, and several kinetic analyses have been used to describe the crystallization process. The regime II→III transition, at a crystallization temperature of 239°, is found. The values of the nucleation parameter K_g for regimes II and III are estimated. The lateral‐surface free energy, σ = 3.24 erg cm^?2, the fold‐surface free energy, σ_e = 52.3 ± 4.2 erg cm^?2, and the average work of chain folding, q = 4.49 ± 0.38 kcal/mol, are determined with the (040) plane assumed to be the growth plane. The observed crystallization characteristics of syndiotactic polystyrene are compared with those of isotactic polystyrene. The activation energies of isothermal and nonisothermal melt crystallization are determined to be ΔE = ?830.7 kJ/mol and ΔE = ?315.9 kJ/mol, respectively. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 83: 2528–2538, 2002     

Preparation and characterization of low molecular weight silk fibroin by high‐temperature and high‐pressure method

A low molecular weight silk fibroin powder (LMSF) was prepared through high temperature (200°C) and high pressure (20 kgf/cm²), without any addition of chemicals. The carbonized adducts produced during this process were then removed by treatment with activated charcoal. The yield of LMSF by this preparation method was over 60% after the removal of carbonized adducts by using activated charcoal. Amino acid analysis showed an observable decrease in contents of serine and tyrosine in LMSF prepared by this method, as compared to those prepared by neutral salt. The molecular weight of this LMSF was also observably decreased with an increase in the reaction time. From the measurements of differential scanning calorimeter (DSC) and thermal gravimetric analyzer (TGA), thermal properties of LMSF through high temperature and high pressure were also decreased as compared to those produced by neutral salts. In addition, wide‐angle X‐ray diffraction (WAXD) patterns showed that the crystallinity of LMSF differed from that of the original silk fibroin. It can be said that the preparation method of LMSF in this study is a simple, economical, and environmentally compatible process with many advantages. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 85: 2890–2895, 2002     

Non‐isothermal crystallization kinetics of cork‐polymer composites for injection molding

The non‐isothermal crystallization behavior of cork–polymer composites (CPC) based on polypropylene (PP) matrix was studied. Using differential scanning calorimetry (DSC), the crystallization behavior of CPC with 15 wt % cork powder at different cooling rates (5, 10, 15, and 20 °C/min) was studied. The effect of a coupling agent based on maleic anhydride was also analyzed. A composite (PPg) containing polypropylene grafted maleic anhydride (PPgMA) and PP was prepared for comparison purposes. Crystallization kinetic behavior was studied by Avrami, Ozawa, Liu, and Kissinger methods. The Ozawa method fails to describe the behavior of these composites. Results show that cork powder surface acts as a nucleating agent during non‐isothermal crystallization, while the addition of PPgMA decreases the crystallization rate. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 44124.     

Melt spinning of poly(vinylidene fluoride) fibers and the influence of spinning parameters on β‐phase crystallinity

The effects of melt‐spinning and cold‐drawing parameters on the formation of β‐phase crystallinity in poly(vinylidene fluoride) (PVDF) fibers and ways of increasing such crystallinity were studied. Fibers were melt‐spun with four different melt draw ratios (MDRs) and were subsequently cold‐drawn at different draw ratios (λ). The maximum λ value in cold drawing was dependent on the MDR used in melt spinning. The crystalline structure of the fibers was studied mainly with differential scanning calorimetry (DSC) and X‐ray diffraction (XRD). The results showed that the degree of crystallinity in the fibers was determined by the MDR and that before cold drawing the crystalline structure of the fibers was predominantly in the α form. By cold drawing, α‐phase crystallites could be transformed into the β phase. It was established that, under certain conditions of melt spinning and cold drawing, PVDF fibers of up to 80% crystallinity, mainly in the β form, could be prepared. It was further proposed that fibers spun at a sufficiently high MDR consist to a large extent of extended‐chain crystals, and this greatly affects the melting point of PVDF. Thus, DSC melting‐point data were shown to be insufficient for determining the crystalline phase of PVDF. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Rheological,thermal, and morphological properties of low‐density polyethylene/ultra‐high‐molecular‐weight polyethylene and linear low‐density polyethylene/ultra‐high‐molecular‐weight polyethylene blends

The dynamic rheological behavior of low‐density polyethylene (LDPE)/ultra‐high‐molecular‐weight polyethylene (UHMWPE) blends and linear low‐density polyethylene (LLDPE)/UHMWPE blends was measured in a parallel‐plate rheometer at 180, 190, and 200°C. Analysis of the log–additivity rule, Cole–Cole plots, Han curves, and Van Gurp curves of the LDPE/UHMWPE blends indicated that the blends were miscible in the melt. In contrast, the rheological properties of LLDPE/UHMWPE showed that the miscibility of the blends was decided by the composition of LLDPE. The differential scanning calorimetry results and scanning electron microscopy photos of the LLDPE/UHMWPE blends were consistent with the rheological properties, whereas with regard to the thermal and morphological properties of LDPE/UHMWPE blends, the results reveal three endothermic peaks and phase separation, which indicated a liquid–solid phase separation in the LDPE/UHMWPE blends. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

Protection of high‐density polyethylene–silicon composites from ultraviolet–visible photodegradation

The extent of the ultraviolet–visible (UV–vis) photoirradiation effect on high‐density polyethylene (HDPE) and HDPE–silicon (Si) composites is reported in terms of the addition of Si microparticles at contents of 0.1, 1, and 5 wt %. A standard accelerated UV–vis exposure was applied over 2750 h, corresponding to 22 months in Florida. Thermogravimetry, differential scanning calorimetry, and Fourier transform infrared spectroscopy were used as reliable techniques for monitoring the quality of the HDPE–Si composites. The increasing addition of Si microparticles delayed the photodegradation of the HDPE–Si composites. Because of their strong light‐scattering effects, Si microparticles blocked the degradation of tertiary carbons of the HDPE backbone and reduced the apparition of vinyl groups; this prevented the structural impoverishment of HDPE–Si composites. Consequently, variations in the crystallization temperature (T_c) and melting temperature (T_m), which were indicators of photodegradation, were not modified. In general, the HDPE–Si composite formulation with 5 wt % Si microparticles was useful for protecting the material from photodegradation and, thus, should be an environmentally friendly, reliable alternative UV–vis blocker. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134, 45439.     

Isothermal crystallization kinetics of high‐flow nylon 6 by differential scanning calorimetry

The isothermal crystallization kinetics have been investigated with differential scanning calorimetry for high‐flow nylon 6, which was prepared with the mother salt of polyamidoamine dendrimers and p‐phthalic acid, an end‐capping agent, and ε‐caprolactam by in situ polymerization. The Avrami equation has been adopted to study the crystallization kinetics. In comparison with pure nylon 6, the high‐flow nylon 6 has a lower crystallization rate, which varies with the generation and content of polyamidoamine units in the nylon 6 matrix. The traditional analysis indicates that the values of the Avrami parameters calculated from the half‐time of crystallization might be more in agreement with the actual crystallization mechanism than the parameters determined from the Avrami plots. The Avrami exponents of the high‐flow nylon 6 range from 2.1 to 2.4, and this means that the crystallization of the high‐flow nylon 6 is a two‐dimensional growth process. The activation energies of the high‐flow nylon 6, which were determined by the Arrhenius method, range from ?293 to ?382 kJ/mol. The activation energies decrease with the increase in the generation of polyamidoamine units but increase with the increase in the content of polyamidoamine units in the nylon 6 matrix. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

A DMA study of the interfacial changes on injection‐molded iPP/mica composites modified by a p‐phenylen‐bis‐maleamic acid grafted atactic polypropylene

Present work concerns to the study of the dynamic mechanical and thermal responses of selected polypropylene (iPP)/mica composites with a modified interface from the matrix side by using a p‐phenylen‐bis‐maleamic acid grafted atactic polypropylene, coming from a byproduct of industrial polymerization reactors. Thus, the study is mainly focused on the 75/25 iPP/mica ratio since it was identified in previous works as providing the maximum inter mica particle distance to assure they should participate in the overall process of dissipation of the mechanical energy supplied to the composites. Hence, the present dynamic mechanical analysis discussion tries to correlate the damping responses of the injection‐molded composites with those previously obtained but over compression molded composites as the basis of further studies all along the compositional iPP/mica map. Therefore, the latter let us, on the one hand, to follow how the main values of the different dynamic mechanical analysis parameters vary because of the interfacial modifier presence, and on the other, to develop a robust correlation between them and the corresponding macroscopic mechanical parameters. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134, 45366.     

Characterization of the free volume in high‐impact polystyrene/polypropylene and high‐impact polystyrene/high‐density polyethylene blends probed by positron annihilation spectroscopy

The free‐volume properties of high‐impact polystyrene (HIPS)/polypropylene (PP) and HIPS/high‐density polyethylene (HDPE) blends were investigated by means of positron annihilation lifetime spectroscopy (PALS). The measured results show that the free‐volume holes in the semicrystalline polymers, such as PP and HDPE, were not large enough to accommodate the branched chains and the end groups of the macromolecular chains in HIPS to produce favorable interactions between the semicrystalline polymers and the HIPS polymer in these blends; thus immiscible blends were formed. The weak interaction between two dissimilar polymer molecules only took place in the regions between two amorphous phases. In addition, the observed negative deviations of the longest lifetime intensity and the free‐volume fraction were attributed to the influence of the interfacial polarization during PALS measurement. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 90: 1507–1514, 2003     

Chemical and thermal characterization of high‐ and low‐density irradiated polyethylenes

A comparative study of the dynamic mechanical relaxation spectra of high‐ and low‐density polyethylenes irradiated with γ‐radiation from a Co⁶⁰ source was performed. The irradiation doses ranged from 0 to 100 Mrad. All the samples were previously characterized by determination of the molecular weight distribution, the number of functional groups, and the crystalline fraction. All the relaxation zones between ?145°C and the melt were studied in the frequency range from 0.3 to 30 Hz. The changes observed in the mechanical relaxation spectra were related to modifications in the chemical structure and morphological parameters attributed to the exposure of the samples to the γ‐radiation. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 86: 1953–1958, 2002     

Rheological behavior of high‐density polyethylene (HDPE) filled with paper mill sludge

A comparative study was conducted of composites made with sludge from three different paper mills. Sludges were obtained from a thermomechanical pulp (TMP), a chemico‐TMP (CTMP), and a Kraft mill with a feedstock of primarily black spruce. The primary sludge (PS) and secondary sludge (SS) were mixed at two different ratios (PS:SS = 7:3 and 9:1) and blended with high‐density polyethylene (HDPE) at 20%, 30%, and 40% proportion. The blends were tested using plate–plate geometry before subjection to frequency sweep by oscillation rheometry. The storage modulus (G′), loss modulus (G″), and complex viscosity (η*) increased with increasing paper sludge content. Decreasing the PS:SS ratio from 9:1 to 7:3 decreased G′, G″, and η*. Differential scanning calorimetry showed that sludge addition increased both the melting and crystallization temperature, for a positive effect on crystallinity. Although the behavior of sludge–high‐density polyethylene blends differed from that of traditional wood plastic composite made with wood flour, they obtained G′, G″, and η* values of the same magnitude. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018 , 135, 46484.     

Effect of 1,3,5‐trialkyl‐benzenetricarboxylamide on the crystallization of poly(lactic acid)

A series of 1,3,5‐trialkyl‐benzenetricarboxylamides (BTA‐Rs) with different side‐chain lengths of n‐alkyl are synthesized to use as nucleating agents of poly (lactic acid) (PLA). Crystallization rate of PLA is detailed discussed in nonisothermal melt‐crystallization with addition of the synthesized nucleating agents. Among these BTA‐Rs, BTA‐n‐butyl (BTA‐nBu) shows the most excellent nucleation ability for PLA. The influences of BTA‐nBu on the nonisothermal melt‐crystallization and cold‐crystallization from the glassy state, isothermal crystallization, crystalline structure, and spherulite morphology of PLA are investigated. It is found that 0.8 wt % is the optimal weight fraction of BTA‐nBu to improve the crystallization of PLA. In the case of isothermal melt‐crystallization from melt, the addition of BTA‐nBu shortens the crystallization half‐time and speeds up the crystallization rate of PLA with no discernible effect on the crystalline structure. Besides, BTA‐nBu nucleated PLA exhibits smaller spherulites size and larger nucleation density than that of pure PLA. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 130: 1328‐1336, 2013     

Influence of various reaction media on the thermal and rheological properties of poly(acrylamide‐co‐N‐hexadecylacrylamide)

A hydrophobically modified polyacrylamide (PAM) was synthesized by the copolymerization of acrylamide (Am) and N‐hexadecylacrylamide (hAm) through solution copolymerization in a polar organic solvent. Polymer synthesis was performed in three nonaqueous media, including dimethyl sulfoxide (DMSO), a mixture of DMSO and an anionic surfactant such as sodium dodecyl sulfate, and a mixture of DMSO and an acidic surfactant such as dodecyl benzene sulfonic acid. The obtained copolymer, poly(acrylamide‐co‐N‐hexadecylacrylamide) [poly(Am‐co‐hAm)], was characterized by ¹H‐NMR. The physical properties of poly(Am‐co‐hAm)s synthesized in different media were compared with those of PAM and with each other by viscosity measurement, X‐ray diffraction, thermogravimetric analysis, and differential scanning calorimetry. We investigated the ways in which the polymerization medium affected the hydrophobic distribution within the resulting copolymer structure. This aspect, in turn, should have altered the solution properties and the microstructure of the copolymer. For this purpose, we studied the viscometric behavior in diluted solutions, the thermal behavior and thermal stability of the copolymers, and finally, the crystalline structure of the copolymers. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2014 , 131, 39939.     

Effect of poly(styrene‐co‐maleic anhydride) imidization on the miscibility and phase‐separation temperatures of poly(styrene‐co‐maleic anhydride)/poly(vinyl methyl ether) and poly(styrene‐co‐maleic anhydride)/ poly(methyl methacrylate) blends

The objective of this work was to study the miscibility and phase‐separation temperatures of poly(styrene‐co‐maleic anhydride) (SMA)/poly(vinyl methyl ether) (PVME) and SMA/poly(methyl methacrylate) (PMMA) blends with differential scanning calorimetry and small‐angle light scattering techniques. We focused on the effect of SMA partial imidization with aniline on the miscibility and phase‐separation temperatures of these blends. The SMA imidization reaction led to a partially imidized styrene N‐phenyl succinimide copolymer (SMI) with a degree of conversion of 49% and a decomposition temperature higher than that of SMA by about 20°C. We observed that both SMI/PVME and SMI/PMMA blends had lower critical solution temperature behavior. The imidization of SMA increased the phase‐separation temperature of the SMA/PVME blend and decreased that of the SMA/PMMA blend. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Crystallization and thermal properties of biodegradable polyurethanes based on poly[(R)‐3‐hydroxybutyrate] and their composites with chitin whiskers

A series of biodegradable polyurethanes (PUs) were synthesized from hydroxylated bacterial poly[(R)‐3‐hydroxybutyrate], P[(R)‐HB]‐diol, as crystallizable hard segment and hydroxyl‐terminated synthetic poly[(R,S)‐3‐hydroxybutyrate), P[(R,S)‐HB]‐diol, as an amorphous soft segment, using 1,6‐hexamethylene diisocyanate, as non‐toxic connecting agent. The P[(R)‐HB] content was varied from 30 to 70 wt %. The resulting copolymers were characterized by FT‐IR, ¹H‐NMR, DSC, and TGA. The DSC data revealed that the melting of P[(R)‐HB] segment increases with increasing its own content in the PUs. The cold and melt crystallization are enhanced with increasing P[(R)‐HB] content. The TGA data revealed that the thermal decomposition mainly occurred via a single degradation step and the thermal stability slightly increased with increasing P[(R)‐HB] content. The non‐isothermal crystallization behavior of PU sample containing 40 wt % PHB with and without α‐Chitin whiskers was studied using DSC, and their kinetics data were investigated via the Avrami, Ozawa, and Z.S. Mo methods, respectively. Crystallization activation energy was estimated using Kissinger's method. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 40784.     

Emulsion‐electrospinning n‐octadecane/silk composite fiber as environmental‐friendly form‐stable phase change materials

The ultrafine n‐octadecane/silk composite fibers as form‐stable phase change materials were successfully developed by the emulsion‐electrospinning method. The effect of n‐octadecane content in the emulsion on the morphology and thermal energy storage capacity of the composite fibers were scientifically investigated. Scanning electron microscopy images show that the composite fibers display cylindrical shape with smooth surface and uniform diameter. Differential scanning calorimetry results demonstrate that the composite fibers exhibit reversible phase transition behavior, high thermal energy storage capacity, and good thermal reliability. Meanwhile, the composite fibers exhibit the capability to regulate their interior temperature as the ambient temperature alters according to the thermo‐infrared images. In addition, the composite fibers are friendly to the environment due to the biodegradability of silk. Therefore, the n‐octadecane /silk composite fibers have the great potential application of serving as form‐stable phase change materials for thermal energy storage and thermal regulation. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134, 45538.