Changes In Degree Of Crystallinity Research Articles

Effect of graphite filler on the physiochemical properties of graphite reinforced thermoset rooflite – unsaturated polyester resin composites

It is well known that many polymers are insulators with poor mechanical properties, which limit their use in fuel cell applications. Physicochemical properties of the polymers can be improved by adding conductive fillers. Carbon-based materials like graphite, which provides excellent mechanical strength and thermal conductivity to the polymer matrices, is of special interest because of its abundance, low cost and light weight when compared to other carbon allotropes. In the present work we describe the physicochemical properties of rooflite unsaturated polyester resin/graphite composites. Rooflite resin and three of its composites containing 1%, 3% and 5% of graphite by weight (C-2, C-3, and C-4, respectively) were synthesized and characterized by FTIR spectral data. XRD showed two peaks at 2q = 27.37°and 55.40° with d spacing value of 3.2559 nm and 1.6571 nm, respectively, indicating the change in degree of crystallinity of the composite. The calculated crystallinity for the resin is 7.3%, and for C-2, C-3 and C-4 its values are 12.1%, 14.3%, 17.1%, respectively, evidencing the interactions between the graphite and polymer matrix. The composites showed fractured surfaces and porous rough structure with randomly distributed vascularized cavities. Agglomeration occurs, when the concentration of graphite increases. The glass transition temperature for the pure resin is 65.9 °C and increases when the resin is filled with graphite. Thermogravimetric analysis (TGA) of the composites showed no marked difference between Tmax and Tfinal, and LOI values of C-3 and C-4 are above 21%, making them self-extinguishable materials that could be used for making bipolar plates. The chemical resistance investigation against water, NaCl, NaOH, acetic acid, and toluene showed more resistance to acid than alkali solutions. These rooflite resin/graphite composites could be further studied to explore the possibility of making bipolar plates, which are an essential component of fuel cells.

H‐Bonded Amorphous Polymer Glass Nanofibers with Simultaneously Large Enhancement in Strength, Toughness, Ductility, and Thermal Stability

AbstractUnderstanding the direct effects of hydrogen bonding (H‐bonding) on the mechanical response of glassy state polymers remains a challenge, largely owing to the use of semicrystalline polymers in such studies, wherein, separating the contributions due to the changes in degree of crystallinity and direct H‐bonding effects on the observed mechanical properties is extremely difficult. This limitation is overcome by studying the mechanical behavior of amorphous, glassy polyvinylpyrrolidone (PVP), H‐bonded with tannic acid (TA). Uniaxial tension experiments on individual submicron scale PVP fibers (0.6–1.0 µm diameters) with different TA concentrations are conducted to capture their elasto‐plastic deformation characteristics. Amorphous PVP‐TA complexes exhibited some distinctive trends in elasto‐plastic properties with increasing H‐bond density, which are not observed earlier. These distinctive trends are discussed in terms of the competing effects of H‐bond driven crosslinking and TA‐induced reduction in entanglement density, and their differing roles during elastic and plastic deformation. The improvements in elasto‐plastic properties (particularly ductility and toughness) are simultaneously accompanied by uniquely significant thermal stability (i.e., glass transition temperature, Tg) improvements, that can help improve the practical applicability, operational life, and performance of these materials.

Mechanical properties of rCB-pigment masterbatch in rLDPE: The effect of processing aids and water absorption test

Abstract Homogenization of pigment is the key to coloring a plastic product evenly. In this article, the tensile properties of recovered carbon black merge with low molecular weight lubricants and other compounding ingredients in the form of pigment masterbatch (PM) added in a recycled low-density polyethylene (rLDPE) resin were evaluated. The prepared masterbatch with the varying amount and types of processing aids (A and B) was first compounded using the heated two-roll mill. Subsequently, the manually mixed masterbatch in rLDPE was put through an injection molding machine for the shaping process to produce an rLDPE pigment masterbatch composite (PMC). The tensile test was performed on the samples to evaluate the mechanical properties of the PMC. Meanwhile, the melt flow index test was executed to justify the composite flow characteristics. Fourier-transform infrared spectroscopy analysis and scanning electron microscopy were also carried out to analyze the PM and PMC chemical properties and their constructed surface morphology. Besides, X-ray diffraction analysis was performed to determine the changes in degree of crystallinity before and after the water absorption test. The addition of PM in rLDPE has slightly increased the rLDPE matrix tensile properties. While, the usage of more processing aid B in the PMC has turned out to secure better tensile properties compared to the addition of higher amount of processing aid A in the PMC. Interestingly, the tensile properties of all composites after the water absorption test were enhanced, suggesting that a stronger bond was formed during the immersion period.

THERMAL COMPRESSION EFFECT ON SEVERAL PROPERTIES OF 8-YEAR-OLD WARU GUNUNG (HIBISCUS MACROPHYLLLUS) WOOD

The study aimed to investigate the effect of thermal compression on the properties of 8-year-old waru gunung wood. Wood specimens with the dimension of 25 mm100 mm150 mm in thickness, width and length, respectively were heated at 180 ˚C and 200 ˚C for 4 h. During the heating process, the specimens were subsequently compressed at 2.452 N mm−2 for 40 mins at each temperature. Changes in the wood chemical structure were examined using the pyrolysis-gas chromatography-mass spectrometry, the wood physical properties were tested according to ASTM D143-94, the wood surface hardness was tested using a Universal Testing Machine and the wood discoloration was examined using the CIELab method. The changes in crystallinity degree was examined using x-ray diffraction and cell structure were collected as supporting data. Results showed that the thermal compression at 180 ˚C and 200 ˚C caused severe degradation on the specimen carbohydrate but less for lignin. The sum effect of thermal compression on the specimens also consecutively increased the density by 34.24% and 41.87% and surface hardness by 52.78% and 63.09% and decreased the swelling thickness by 38.54% and 47.03% and the equilibrium moisture content by 36.53% and 38.59% at 180 ˚C and 200 ˚C, respectively. Thermally compressed specimens also had darker colours, glossier surfaces and smoother texture compared to non-thermally compressed specimens.

Fabrication, physico-chemical characterization, and bioactivity evaluation of chitosan-linalool composite nano-matrix as innovative controlled release delivery system for food preservation

The aim of the present study was to encapsulate linalool into chitosan nanocomposite (Nm-linalool) for developing novel controlled release delivery system in order to protect stored rice against fungal infestation, aflatoxin B1 (AFB1) contamination, and lipid peroxidation. The chitosan-linalool nanocomposite showed spherical shapes, smooth surface with monomodal distribution as revealed by SEM and AFM investigation. FTIR and XRD represented peak shifting and changes in degree of crystallinity after incorporation of linalool into chitosan nanocomposite. Nanoencapsulation of linalool showed higher zeta potential and lowered polydispersity index. TGA analysis reflected the stability of Nm-linalool with reduced weight loss at varying temperatures. Biphasic pattern, with initial rapid release followed by sustained release illustrated controlled delivery of linalool from chitosan nanocomposite, a prerequisite for shelf-life enhancement of stored food products. Chitosan nanocomposite incorporating linalool displayed prominent antifungal and antiaflatoxigenic activity during in vitro as well as in situ investigation in rice with improved antioxidant potentiality. Further, Nm-linalool displayed considerable reduction of lipid peroxidation in rice without exerting any adverse impact on organoleptic attributes. In conclusion, the investigation strengthens the application of chitosan-linalool nanocomposite as an innovative controlled nano-delivery system for its practical application as novel environmentally friendly eco-smart preservative in food and agricultural industries.

Selective localization of nanohydroxyapatite in poly(3-hydroxybutyrate)/polycaprolactone blends composites and its effects on crystallization and molecular dynamics

This work deals with the thermodynamic selective localization of hydroxyapatite nanoparticles (Hap) and its effects on crystallization and molecular dynamics in immiscible polyester blend films based on poly(3-hydroxybutyrate) (PHB, 90 wt%) and polycaprolactone (PCL, 10 wt%). Polymer blend composite films were obtained through solution casting method and characterized by contact angle (surface energy measurements), ultraviolet–visible spectroscopy (UV–Vis), elemental mapping, X-ray diffraction (WAXD), differential scanning calorimetry (DSC), polarized optical microscopy (POM) and time domain nuclear magnetic resonance (TD-NMR) techniques. It was found that hydroxyapatite (Hap) is selectively localized in the PHB phase and consequently, nanoparticles strongly influenced the PHB crystallization behavior. DSC and POM results indicated that hydroxyapatite nanoparticles acted as a nucleating agent. However, no significant changes in crystallinity degree were observed by WAXD. Fractionated crystallization behavior was observed for PCL droplets and the increase in the Hap concentration promoted heterogeneous nucleation on the droplets surface due to the nanoparticles close to the interface. Molecular dynamics studies by TD-NMR suggested a disordered Hap nanoparticles distribution inside the polymer matrix, leading to slower dynamics in the semirigid fraction of the sample´s magnetization, typically attributed to restricted polymeric chains close to the particle’s surface.

Novel Starch/Chitosan/Aloe Vera Composites as Promising Biopackaging Materials

Edible films based on potato starch, chitosan and Aloe vera gel (AV) as modifiers were evaluated towards their potential application in food or cosmetics industry. The films, with different AV gel concentration were prepared by casting method. The influence of UV radiation on samples chemical structure was analyzed. The surface morphology was observed with AFM method. The chemical structure and molecular arrangement of mixture components were analyzed with ATR–FTIR spectroscopy and X-ray diffraction. Hydrogen bond interactions among the film components, conformational rearrangements as well as changes in crystallinity degree were confirmed. A study of thermal resistance showed the delay of degradation observed together with an increase AV gel amount and after UV-irradiation. The hydrophilic character of the samples was proved. Water solubility slightly depends on the AV concentration in films, and it decrease after UV-irradiation. All the samples with AV gain the increase resistance to microbial action.

Development of Nateglinide Loaded Graphene Oxide-Chitosan Nanocomposites: Optimization by Box Behnken Design

Background:Nateglinide is an antidiabetic drug having biological half-life 1.5 h which shows a concise effect. Graphene oxide along with chitosan can be used as a nanocarrier for sustained release of Nateglinide.Objective:To develop Nateglinide loaded graphene oxide-chitosan nanocomposites and to evaluate for different characterization studies.Methods:Graphene Oxide (GO) was synthesized by improved hummer’s method and drug-loaded Graphene oxide - chitosan nanocomposites were prepared. Box Behnken design was used to carry out experiments. The nanocomposites were characterized for encapsulation efficiency and drug release. Morphology was studied using field emission scanning electron microscope and transmission electron microscope. An interaction between drug, polymer and GO was investigated by Fourier transform infrared spectroscopy and X-ray diffractometer along with in vitro drug release study.Results:The statistical evaluation of the design showed linear and quadratic models which are significant models for encapsulation efficiency (R1 0.6883, 0.9473) and drug loading (R2 0.6785, 0.9336), respectively. Fourier transform infrared spectroscopy showed the compatibility of GO, Chitosan and Nateglinide. X-ray diffractometer reveals the change in degree of crystallinity of drug. FE-SEM and TEM images confirmed the distribution of the drug within the nanocomposites. Design expert reveals that the concentration of GO has great influence on encapsulation efficiency. In Vitro drug release showed the sustained release of drug over the period of 12 h.Conclusion:GO-Chitosan nanocomposites can be used as a sustained release carrier system for Nateglinide to reduce dose frequency of drug as well as its probable side effects.

Radiation-Induced Changes in the Degree of Crystallinity of Powdered Polytetrafluoroethylene

An analysis of the diffraction patterns of powdered polytetrafluoroethylene (PTFE) γ-irradiated at room temperature in a nitrogen atmosphere to doses of 10–500 kGy with a fluence of 1.50 ± 0.3 Gy/s has shown that the diffraction peak 100 of the crystalline phase at 2θ ∼ 18° and the halo at 2θ = 10°–25° are most sensitive to ionizing radiation. It is found that the intensity, FWHM, and position of the maximum of reflection 100 change with an increase in the absorbed dose; this fact is indicative of the doublet nature of the peak profile. It is established that the doublet components differently response to ionizing radiation. The interplanar spacings, amplitude and sign of arising stress, and the degree of crystallinity (DOC) of polymer are calculated as functions of the irradiation dose. The radiation-induced change in the DOC of PTFE should be considered as a complex process, which includes radiative destruction and topochemical reactions of different types in crystals.

Kinetic studies of biocatalyzed copolyesters of poly(butylene succinate) (PBS) containing fully bio-based dilinoleic diol

A series of segmented bio-copolyesters based on crystallizable hard segments of poly(butylene succinate) (PBS) and fully bio-based dilinoleic diol (DLAOH), creating dilinoleic succinate (DLS) soft segments, were prepared by enzymatically catalyzed polycondensation. The kinetic studies performed with 1H NMR and SEC have proved incorporation of highly hydrophobic DLAOH into the polymer backbone. We found that the efficacy of DLAOH incorporation was limited by the catalytic pocket size of the enzyme and its hydrophobic nature favouring the formation of long PBS sequences, especially at the early synthesis stages and having an effect on final content of soft segments compared to feed ratio. Based on quantitative 13C NMR analysis we found that copolymers had R-values lower than 1, that is low degree of randomness. Differential scanning calorimetry (DSC) revealed changes in degree of crystallinity and the presence of a phase mixed system.

Structural, Optical and Electrical Studies on Hybrid Material of In Situ Formed Silver sulfide in Polymer Blend Matrix

Organic–inorganic polymer hybrid films were prepared, using polyvinyl alcohol–polyethylene glycol blend as the organic host matrix. Silver sulfide (Ag2S) semiconductor particles have been synthesized in polymer blend matrix, by in-situ method. Polymer hybrid films, with various amounts of Ag2S were prepared and characterized structurally, optically and electronically by using various characterization techniques, such as Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), Scanning electron microscopy (SEM), UV–Vis absorption spectroscopy, temperature and time dependent DC electrical studies. Hydrogen bonding interactions take place between hydroxyl groups (OH) and carbonyl groups (C=O) of polymer blend molecules with Ag+ ion of Ag2S filler, indicating complex formation between polymer matrix and filler, which is confirmed by FTIR technique. XRD results showed presence of additional multiple peaks (compared to pure blend film) corresponding to αʹ-Ag2S monoclinic crystal system. Changes in degree of crystallinity (%C) are observed for hybrid films with various amounts of Ag2S, showing a highest value of 18.2% for the film containing 0.372 g of Ag2S, when compared to 13.45% (%C) for pure blend film. Uniform distribution of Ag2S nanoparticles in polymer blend matrix is revealed by SEM analysis for hybrid film containing 0.372 g of Ag2S. UV–Vis absorption studies showed multiple absorption peaks due to added filler. Highest value of room temperature conductivity of 9.40 × 10−7 S/cm was obtained for the hybrid film containing 0.372 g of Ag2S. Values of transference numbers (tion and tele) in time dependent electrical studies indicated that the electrical conductivity in pure blend film as well as hybrid films is mainly due to ions.

Enzymatic Degradation of Poly(butylene succinate) Copolyesters Synthesized with the Use of Candida antarctica Lipase B.

Biodegradable polymers are an active area of investigation, particularly ones that can be produced from sustainable, biobased monomers, such as copolymers of poly(butylene succinate) (PBS). In this study, we examine the enzymatic degradation of poly(butylene succinate-dilinoleic succinate) (PBS-DLS) copolymers obtained by “green” enzymatic synthesis using lipase B from Candida antarctica (CALB). The copolymers differed in their hard to soft segments ratio, from 70:30 to 50:50 wt %. Enzymatic degradation was carried out on electrospun membranes (scaffolds) and compression-moulded films using lipase from Pseudomomas cepacia. Poly(ε-caprolactone) (PCL) was used as a reference aliphatic polyester. The degradation process was monitored gravimetrically via water uptake and mass loss. After 24 days, approx. 40% mass loss was observed for fibrous materials prepared from the PBS-DLS 70:30 copolymer, as compared to approx. 10% mass loss for PBS-DLS 50:50. Infrared spectroscopy (FTIR) and size exclusion chromatography (SEC) analysis were used to examine changes in chemical structure. Differential scanning calorimetry (DSC) and scanning light microscopy (LSM) revealed changes in degree of crystallinity, and changes in surface morphology, consistent with a surface erosion mechanism. We conclude that the obtained copolymers are suitable for tissue engineering applications thanks to tuneable degradation and lack of acidification during breakdown.

Aging and arsenite loading control arsenic mobility from ferrihydrite-arsenite coprecipitates

Iron (oxyhydr)oxides may act as a sink and source of arsenic (As) in terrestrial and aquatic systems, therefore studying the mechanisms controlling Fe (oxyhydr)oxide transformation under changing environmental conditions is essential for elucidating the fate of As, in terms of release, mobility and speciation. We provide evidence that aging and As(III) loading control the mineralogical and structural evolution of As(III)-bearing Fe (oxyhydr)oxides, and thus influence the extraction of As with compounds which frequently occur in soil solution. During a one year timeframe, partial As(III) oxidation to As(V) and accumulation on poorly crystalline Fe (oxyhydr)oxides were promoted by increasing As(III) contents, which hindered the transformation of less into more crystalline materials. The changes in crystallinity degree and surface properties resulted in the release of different proportions of As(III) and As(V) from the aged compared to the fresh coprecipitates. The extraction of both As species through mechanisms of competition, disaggregation of Fe (oxyhydr)oxides, or both was assessed by employing several anions, whose efficiency decreased in the order: inorganic phosphate> citrate> organic phosphate> chloride≥silicate. The tested extractants are key components of environments such as aquifers, waterlogged soils or the rhizosphere of paddy soils, where aqueous As(III) is mobilized from the anoxic soil layers and sequestered by Fe (oxyhydr)oxides under more oxidizing environments.

On the comparison of changes induced in crystallinity and surface nanomechanical properties of ultra high molecular weight polyethylene by γ and swift heavy ion irradiations

In this work the influence of two different irradiation techniques on the degree of crystallinity and nanomechanical properties of a medical grade UHMWPE is compared. One technique, widely used in the production of components for total joint replacement, is comprised by γ-irradiation followed by a thermal treatment above the melting temperature of UHMWPE and thus modifies the material's bulk. The other one, an alternative modification technique that affects only the near surface layers of UHMWPE, is swift heavy ion (SHI) irradiation. The effect of two types of ion beams (nitrogen and lithium) with different energies (33 and 47MeV) and fluences (1011 to 1013 ions/cm2) is investigated. Changes in degree of crystallinity are investigated by DSC and Raman spectroscopy while the nanomechanical properties – elastic modulus and hardness – are evaluated by nanoindentation tests. The γ-irradiated and remelted sample exhibits lower degree of crystallinity than the pristine material due to the hindered recrystallization process of the crosslinked chains. Concomitantly, this sample shows a reduction in hardness and elastic modulus of the bulk. On the other hand, SHI-irradiated samples display a large increase in degree of crystallinity and surface mechanical parameters with respect to pristine UHMWPE. The modification is confined to the ion target depth. The layer affected by the ion beam shows constant mechanical properties that appeared to be slightly influenced by the fluence in the studied range (around the optimum). Despite the changes induced by both techniques are completely different, they are able to enhance the wear performance of UHMWPE due to the beneficial change in elastic to plastic properties. Among SHI-irradiated samples, the N-ion (33MeV and 1×1012 ions/cm2) exhibits the better combination of nanomechanical properties.

In situ crystallization of high performing WO3-based electrochromic materials and the importance for durability and switching kinetics

A chemical self-assembled synthesis was used to prepare disordered porous semicrystalline WO3-based cathodic electrochromic films. The resulting films were characterized with transmission electron microscopy (TEM), scanning electron microscopy (SEM), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), N2 physisorption, Fourier transform infrared spectroscopy (FTIR) and near-edge X-ray absorption fine structure (NEXAFS). The electrochromic performance was evaluated in a Li-ion electrolyte (i.e., 1 M LiClO4 dissolved in propylene carbonate) with cyclic voltammetry (CV), galvanostatic cycling with potential limitation (GCPL) and chronoamperometry (CA) techniques. It is demonstrated that the crystallinity of WO3 thin films can be readily tuned with the variation of annealing temperatures and TiO2 addition. The results demonstrated excellent stability and durability (i.e., 1500 GCPL cycles in 32 days) for WO3 electrode annealed at 350 °C, ultrafast switching kinetics for WO3–TiO2 electrode (i.e., bleaching and coloration times are 5.5 s and 4.2 s, respectively) and excellent charge reversibility (%R ≈ 100%). Electrochemical, TEM and Raman spectroscopy studies suggest that a change in degree of crystallinity in WO3 occurs during the extended durability test, which then influences the durability and switching kinetics.

Photochemical transformation in poly(acrylic acid)/poly(ethylene oxide) complexes

The poly(acrylic acid)/poly(ethylene oxide) (PAA/PEO) complexes with different stoichiometric ratio were obtained from aqueous solutions. The chemical structure of these blends in solid state and the interactions between components has been studied using mainly FT-IR spectroscopy. The miscibility of components was proved also by differential scanning calorimetry (DSC). The films of both pure polymers and their blends at different compositions were UV-irradiated ( λ = 254 nm) in air atmosphere. The course of photochemical transformations has been monitored by absorption spectroscopy (FT-IR, UV–vis), DSC, X-ray diffraction and thermogravimetry, which was also applied for estimation of the thermal properties of samples studied. It was found that photooxidative degradation is less efficient in PAA/PEO complexes than that in PAA and PEO exposed separately. The most photostable was PAA/PEO (50/50) blend. PAA disturbs crystallization PEO in the blends but changes in crystallinity degree of PEO/PAA during UV-radiation were negligible. Thermal stability of PAA/PEO complexes is lower comparing to pure components but UV-irradiation does not cause significant changes in thermal resistance of blends studied.

PHYSICAL AND BARRIER PROPERTIES OF DEVELOPED BILAYER PROTEIN FILMS

The effects of three bilayer–forming methods (liquid protein spread on dry film, heat pressing dry films, and solvent laminating dry films) on physical and barrier properties were investigated. These bilayer films were generated using soy protein isolate, wheat gluten protein, and corn zein protein. Bilayer films were evaluated for enhanced properties (tensile strength, percent elongation, water vapor, and oxygen permeability) over single layer films. Using X–ray crystallography, these films showed no changes in degree of crystallinity. Depending upon film type in this study, protein bilayer films exhibited reduced, similar, and enhanced properties. Hydration properties, solvent and protein interactions, film thickness, surface properties, or heat and pH differences influenced the formation of these films. Water vapor permeability for these films ranged from 1.3
10
9 g m –1 s –1 Pa –1 for soy sprayed on corn film to 3.5
10
9 g m –1 s –1 Pa –1 for solvent laminating wheat and soy films. Oxygen permeability ranged from 2.67
10 –17 moles m m –2 s –1 Pa –1 for spraying soy on corn films to 8.81
10 –19 moles m m –2 s –1 Pa –1 for pouring soy on wheat film. Tensile strength ranged from 1.57 MPa for spraying corn on wheat films to 9.10 MPa for heat pressing wheat and corn films. Elongation ranged from 5.36% for pouring soy on corn films to 204.12% for pouring soy on wheat films. Bilayer films appear to exhibit reduced tensile strength, similar oxygen permeability, enhanced percent elongation, and greatly increased water vapor permeability.

Understanding isothermal semicrystalline polymer drying: Mathematical models and experimental characterization

The drying mechanism of semicrystalline poly(vinyl alcohol) (PVA) was investigated. PVA samples of various molecular weights were crystallized by annealing at temperatures slightly above the glass transition temperature of PVA, and swollen in water for different time periods. The water volume fraction in the sample was measured using a buoyancy technique. The samples were dried in air at constant temperatures, and the drying kinetics were investigated using thermogravimetric analysis. The change in degree of crystallinity of the swollen polymer during drying was measured by differential scanning calorimetry (DSC) as well as by Fourier transform infrared spectroscopy (FTIR). The degree of crystallinity of the samples increased during drying, which in turn was found to alter the drying rate. The drying kinetics were faster at higher temperatures, for lower molecular weights, and for lower degrees of crystallinity. A mathematical model was developed to predict drying rates of semicrystalline polymers by considering the crystallization kinetics during drying. The model predictions included the thickness of the polymer sample, the degree of crystallinity of the polymer, and the water weight loss as functions of drying time. Model predictions were found to agree reasonably well with the experimental results.

Understanding isothermal semicrystalline polymer drying: Mathematical models and experimental characterization

The drying mechanism of semicrystalline poly(vinyl alcohol) (PVA) was investigated. PVA samples of various molecular weights were crystallized by annealing at temperatures slightly above the glass transition temperature of PVA, and swollen in water for different time periods. The water volume fraction in the sample was measured using a buoyancy technique. The samples were dried in air at constant temperatures, and the drying kinetics were investigated using thermogravimetric analysis. The change in degree of crystallinity of the swollen polymer during drying was measured by differential scanning calorimetry (DSC) as well as by Fourier transform infrared spectroscopy (FTIR). The degree of crystallinity of the samples increased during drying, which in turn was found to alter the drying rate. The drying kinetics were faster at higher temperatures, for lower molecular weights, and for lower degrees of crystallinity. A mathematical model was developed to predict drying rates of semicrystalline polymers by considering the crystallization kinetics during drying. The model predictions included the thickness of the polymer sample, the degree of crystallinity of the polymer, and the water weight loss as functions of drying time. Model predictions were found to agree reasonably well with the experimental results. © 1998 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 36: 2771–2780, 1998

Thermoanalytical study of nucleating effects in polypropylene composites

Engineering application of polypropylene requires the employment of flame retardants. Reactive compounding of ammonium-polyphosphate and synergist additives with polypropylene is an effective way for forming flame retardant polypropylene. Both the ammonium-polyphosphate and the additives used for improving its performance effect the crystallization and melting behavior of polypropylene. Encapsulation of flame retardant additives with appropriate elastomer, in order to improve their water resistancy, causes further changes in degree of crystallinity and consequently in the mechanical properties.