Crystallization and Morphology of Poly(ethylene 2,6‐naphthalene dicarboxylate) Containing Additives

The influence of nucleating agents (AClyn^®, Surlyn^® and sodium benzoate (SB)) alone and together with nucleating promoter (Ceraflour^® 993 and Ceraflour^® 991 and poly(1,4‐butylene sebacate)) on the crystallization and morphology of poly(ethylene 2,6‐naphthalene dicarboxylate) (PEN) was investigated by means of differential scanning calorimeter, polarized optical microscopy and small angle light scattering. It was revealed that AClyn, Surlyn and SB effectively accelerate nucleation and crystallization of PEN with increasing the ratio of nucleating agent up to 1 wt.‐%. A combination of nucleating agent and nucleating promoter leads to further increase in crystallization rate at low temperature, but only a slight change at high temperature. Hedrites were obtained in pure PEN and the addition of SB and Ceraflour 993 produces small crystals with poor perfection upon crystallization in high temperature region. When crystallization temperature was below 210 °C, spherulites were observed in pure PEN and also in the samples of PEN/Ceraflour 993 and PEN/SB but with smaller size.

Crystal morphology of PEN crystallized at 240 °C for 40 min.     

Differential Scanning Calorimetry Study of Blends of Poly(ethylene glycol) with Selected Fatty Acids

A series of blends of poly(ethylene glycol) (PEG) with different molecular weights with: (i) capric, (ii) lauric, (iii) myristic, (iv) palmitic or (v) stearic acid, as a thermal energy storage material, has been investigated by differential scanning calorimetry (DSC). Transition temperatures and latent heat of transition of PEG, fatty acids and their binary blends were determined since these properties are of primary importance in the design of phase change energy storage materials. The experimental results showed that it is possible to obtain homogeneous (as indicated by DSC data) polymer/fatty acid blends by mixing in the melt and subsequent solidification. The melting ranges of PEG/fatty acid systems were observed to be from 30 to 72 °C while their heat of transition lies in the range of 168–208 J · g^?1. Synergistic action of the components was found for PEG 10 000/stearic acid blend – heat of transition was ca. 15 and 35% higher than for pure stearic acid and PEG, respectively. This phenomena may be explained in terms of strengthened specific interactions via hydrogen bonding leading to formation of more perfect crystalline lattice.

DSC melting and freezing curves of blends PEG/lauric acid. 1 ‐ PEG 3 400/lauric acid, 2 ‐ PEG 10 000/lauric acid, 3 ‐ PEG 20 000/lauric acid, 4 ‐ PEG 35 000/lauric acid (cooling ‐ 10 K · min^?1), 5 ‐ PEG 3 400/lauric acid, 6 ‐ PEG 10 000/lauric acid, 7 ‐ PEG 20 000/lauric acid, 8 ‐ PEG 35 000/lauric acid (heating ‐ 10 K · min^?1).     

Cold Crystallization of PLLA Studied by Simultaneous SAXS and WAXS

Summary: The cold crystallization process of initially amorphous poly(L ‐lactic acid), PLLA, with two different molecular weights, during a heating at 2 °C/min, was investigated by DSC and time‐resolved simultaneous SAXS and WAXS, using synchrotron radiation. Equatorial scans of the isotropic 2D‐SAXS patterns showed that the average Bragg long period (L_B) of PLLA samples was approximately constant with the development of cold crystallization up to a temperature that corresponded to a melt/re‐crystallization process that took place before the nominal melting peak seen by DSC. L_B values were found to be higher for the high molecular weight material. This was in accordance with the higher melting temperature observed in the high molecular weight PLLA that implied the existence of thicker lamellae. WAXS results showed that the molecular weight did not apparently affect the crystal form and the final degree of crystallinity of PLLA. The Avrami parameters from WAXS and DSC were consistent, showing that the non‐isothermal cold crystallization of the two PLLA samples corresponded mainly to a three‐dimensional growth, although an imperfect crystallization process was involved at early times. The crystallization rate of PLLA, observed both by WAXS and DSC, decreased with increasing molecular weight.

SAXS profiles of PLLA2 as a function of temperature. The inset shows the 2D‐SAXS pattern obtained at 180 °C.     

Preparation of Micron‐Sized Spherulitic Bisphenol A Polycarbonate Particles in Thin Films

A facile technique is presented to prepare discrete µm‐sized spherulitic particles of BAPC in thin polymer films. Unlike in bulk precipitation or spray crystallization, the present technique offers a method to prepare three‐dimensional semicrystalline particles of narrow particle size distribution that can be readily isolated and collected from the glass substrate as discrete particles. We report the effects of polymer molecular weight, polymer type, and the precursor polymer film thickness on the formation of spherulitic particles and their morphologies. The three‐dimensional spherulitic particles prepared in this study have large specific surface areas, higher crystallinity and melting temperature than the bulk precipitated and crystallized polycarbonate particles.

     

The Influence of the Irradiation Temperature on the Ratio of Chain Scission to Branching Reactions in Electron Beam Irradiated Polytetrafluoroethylene (PTFE)

Polytetrafluoroethylene (PTFE) films have been irradiated by electron beam in vacuum at various temperatures ranging from room temperature up to temperatures far above the melting temperature. Changes of the chemical structure have been analyzed by ¹⁹F solid‐state NMR and IR spectroscopy. The concentration of several structures generated by irradiation increases with increasing irradiation temperature up to the beginning of the thermal degradation. The molar ratio of >CF? branching points to ? CF₃ end groups changes with crossing of the melting temperature. The generation of >CF? branching points is accelerated if the PTFE is irradiated in the molten state, where branching reactions become more important.

     

Dynamic Mechanical Properties of Poly(propylene) Blends with Poly[ethylene‐co‐(methyl acrylate)]

Summary: Blends of poly(propylene) (PP) were prepared with poly[ethylene‐co‐(methyl acrylate)] (EMA) having 9.0 and 21.5% methyl acrylate comonomer. A similar series of blends were compatibilized by using maleic anhydride grafted PP. The morphology and mechanical properties of the blends were investigated using differential scanning calorimetry (DSC) and dynamic mechanical analysis (DMA) in tensile mode. The DMA method and conditions were optimized for polymer film specimens and are discussed in the experimental section. The DSC results showed separate melting that is indicative of phase‐separated blends, analogous to other PP‐polyethylene blends but with the added polarity of methyl acrylate pendant side groups that may be beneficial for chemical resistance. Heterogeneous nucleation of PP was decreased in the blends because of migration of nuclei into the more polar EMA phase. The crystallinity and peak‐melting temperature did not vary significantly, although the width of the melting endotherm increased in the blends indicating a change had occurred to the crystals. DMA analysis showed the crystal‐crystal slip transition and glass transition (T_g) for PP as well as a T_g of the EMA copolymer occurring chronologically toward lower temperatures. The storage modulus of PP and the blends was generally greater with annealing at 150 °C compared with isothermal crystallization at 130 °C. The storage modulus of the blends for isothermally crystallized PP increased with 5% EMA, then decreased for higher amounts of EMA. Annealing caused a decrease with increasing copolymer content. The extent of the trend was greater for the compatibilized blends. The T_g of the blends varied over a small range, although this change was less for the compatibilized blends.

Storage modulus for PP and EMA9.0 blends annealed at 150 °C.     

Physical Properties of Isotactic Poly(propylene)/Silver Nanocomposites: Dynamic Crystallization Behavior and Resultant Morphology

Summary: The presence of silver nanoparticles (0.01–5 wt.‐%) increased the crystallization temperature of isotactic poly(propylene) (iPP) (e.g., a 5 wt.‐% content increases the temperature by ca. 7 °C) and produced a sharper crystalline peak. It had little effect on the melt rheology of the nanocomposites. The shear‐induced crystallization behavior of iPP was accelerated with increasing Ag content and imposed frequency. In addition, the promoting effect of Ag nanoparticles on the overall crystallization behavior was more notable at 140 °C than at 130 °C. The wide‐angle X‐ray diffraction scans of iPP nanocomposites with 5 wt.‐% Ag crystallized at 130 °C clearly presented another peak at a 2θ value of 15.8°, which corresponded to a β‐form crystal. The nanocomposites with 5 wt.‐% Ag crystallized at 130 °C gave double melting peaks at 154 and 166 °C. On the other hand, the samples crystallized at 140 °C produced two melting peaks at 166 and 172 °C. The introduction of as much as 0.1 wt.‐% of Ag nanoparticles increased both the tensile strength and elongation at break, but subsequent further addition caused a decrease. In addition, iPP nanocomposites with more than 1 wt.‐% Ag exhibited a higher modulus than pure iPP.

Time dependence of G′ of iPP and iPP/Ag nanocomposites at 130 °C at ω = 1 rad · s^?1.     

Applicability of Frozen Gels from Ultra High Molecular Weight Polyethylene and Paraffin Waxes as Shape Persistent Solid/Liquid Phase Change Materials

Ultra high molecular weight polyethylene (UHMW‐PE) physically gels molten paraffin waxes (PW) at concentrations exceeding 0.5 wt.‐%. In the composites the paraffin wax crystallises without destruction of the UHME‐PE gel network. Above the melting transition of the paraffin compound the capillary forces prevent the liquid wax from free flow. The composites can be processed by melt extrusion, and injection moulding above the melting temperature of the gel at 116 °C. The thermal and mechanical properties of these UHMW‐PE/paraffin composites have been characterised regarding their applicability as shape persistent phase change materials (PCM). The UHMW‐PE/PW gels can store, and release enthalpies up to 200 J/g at the melting temperature of the PW. In the gel state the liquid alkane can leave the gel when in direct contact to porous materials, and the gels mechanical strength are lower than that of standard polymers. These drawbacks are proposed to overcome by formation of PCM/polymer, or PCM/metal laminates.

Schematic cross section of a proposed PCM laminate consisting of a polymer top‐ and bottom layer enclosing the UHMW‐PE/paraffin gel.     

Colloidal Crystalline Arrays of β‐Polymorphic Poly(vinylidene fluoride)

Stable layers of nearly monodisperse spheres of β‐polymorphic poly(vinylidene fluoride) with iridescent properties are prepared. The colloidal crystalline arrays (CCAs) were characterized by optical microscopy, differential scanning calorimetry (DSC), and FT‐IR spectroscopy. FT‐IR spectroscopic and wide‐angle X‐ray scattering (WAXS) studies revealed a β‐polymorphic PVF₂ structure, the DSC study showed that the level of crystallinity in the CCA was much higher than that in the melt‐crystallized sample, and UV‐visible spectroscopy showed extinction peaks at 323 and 510 nm in the CCAs. The β‐polymorphic PVF₂ structure, along with the optical extinction properties of these CCAs, raises the prospect of their application in optical filters and/or piezoelectric sensors.

Optical micrograph of PVF₂ CCA films cast on glass substrates.     

Preparation and Characterization of Polycarbonate/Poly(propylene)/Attapulgite Ternary Nanocomposites with the Morphology of Encapsulation

Summary: Ternary nanocomposites based on polycarbonate (PC), poly(propylene) (PP), and attapulgite (AT) were prepared via the method of two‐step melt blending, by which the AT was blended with PP prior to compound with PC. Structure and properties of the ternary PC/PP/AT nanocomposites were investigated. The degradation of PC triggered by AT during direct blending process can be inhibited effectively by using two‐step melt blending. It was found that the morphology of encapsulation structure like sandbag was formed in PC matrix, where PP encapsulated AT fibrillar single crystals. DSC experiments showed that in PC/PP/AT ternary nanocomposites, AT had a strong heterophase nucleation effect on PP, resulting in the enhancement of crystallization degree and the crystallization temperature of PP. DMA and mechanical property results showed that the ternary nanocomposites exhibited good balanced toughness and stiffness.

TEM photograph of PC/PP/AT ternary nanocomposite.     

Thermal Characterization of Upper Critical Solution Temperature m‐LLDPE/Poly(ethylene‐ran‐butene) Elastomer Blends

Summary: The phase and thermal characteristics of blends consisting of linear low‐density polyethylene (LLDPE) (0.7 mol‐% hexene copolymer) and poly(ethylene‐ran‐butene) (PEB) (26 mol‐% butene copolymer) have been investigated using optical microscopy (OM), differential scanning calorimetry (DSC), and thermogravimetric analysis (TGA). An upper critical solution temperature of 162 °C was exhibited. The addition of PEB not only slowed the overall crystallization rate of LLDPE but also changed the distribution of lamellar thickness or perfection of LLDPE crystals. The equilibrium melting temperature of LLDPE in the blends was reduced and kept relatively constant in the bi‐phase state. The blends showed a single‐stage degradation and an intermediate thermal stability between those of the individual components. It could be attributed to their homogeneous states at degradation temperatures and the similar decomposing mechanisms of two components. The kinetic analysis of thermal degradation also confirmed the above results.

Phase diagram of LLDPE/PEB blends.     

The Solid State Postcondensation of PET, 4

Summary: A new method of polymerising PET in the solid state is proposed in either a gas phase reactor, or in hydrocarbon dispersion. It is shown that the reaction can be carried out efficiently at temperatures on the order of 200–240 °C directly from a prepolymer without the need for a melt phase step. It is shown that the crystal structure of the prepolymer plays a determining role in the kinetics of the SSP reaction.

Schema of the reactor used for gas phase SSP.     

Spherulitic crystallization behavior of linear low‐density polyethylene

In this study the crystallization behavior of linear low‐density polyethylenes (LLDPEs) (ethylene‐α‐olefin copolymers) was studied by polarized light microscopy. A modified Hoffman‐Lauritzen (MHL) expression is proposed whereby the equilibrium melting temperature, T (T), is replaced with the melting temperature of the crystal stem is replaced with the maximum possible stem length, T. It successfully describes the crystalline spherulitic growth kinetics for both homogeneous and heterogeneous LLDPEs. In addition to regimes III and II, another regime (IM) was found in the high crystallization temperature range. Linear growth behavior of crystalline spherulites was observed in regime III, and nonlinear growth behavior was found in regimes II and IM. The basal surface free energy can be estimated from the short chain branching polydispersity (SCBP) for LLDPEs with excluded comonomers. Polym. Eng. Sci. 45:74–83, 2005. © 2004 Society of Plastics Engineers.     

Effect of Nanoclay Incorporation on the Thermal Properties of Poly(ethylene terephthalate)/Liquid Crystal Polymer Blends

The effect of OMLS incorporation on the thermal properties of PET/LCP blends is studied. Pure and OMLS‐modified PET/LCP blends were prepared by melt‐extrusion using twin‐screw extruder. The morphological analyses of PET/LCP blends show that OMLS addition enhances the phase‐separated structure of the pure blend. A detailed study on the thermal properties of the pure and OMLS‐modified PET/LCP blends were carried out by means of DSC in both conventional and modulation modes. Results show a complex melting behaviour comprises of successive melting and re‐crystallisation. Finally, non‐isothermal crystal‐growth kinetics of pure and OMLS‐modified blends were investigated.

     

Injection Moulding: Evaluation of Appropriate Melt Injection Points for the Gas Injection Technique

In gas assisted injection moulding the melt front advancement has a considerable effect on the gas penetration. The evaluation of an appropriate melt filling is an important step to avoid instabilities in the process sequence. Taking a sample moulded part a procedure is presented that enables the part designer to evaluate required melt and gas injection points according to the gas injection technique. Using finite element simulations, different calculations for the melt front advancement lead to the correct gate location.

Presentation of different degrees of filling for the optimised article geometry.     

Disentangled State in Polymer Melts; a Route to Ultimate Physical and Mechanical Properties

The role of entanglements in obtaining a homogeneous product of ultra high molecular weight polyethylene (UHMW‐PE) has been explored. Studies performed in this report show that a disentangled state before melting is a prerequisite to obtain homogeneous products of an intractable polymer like UHMW‐PE. The disentangled state is obtained directly from the reactor by controlling the polymerisation conditions or in the solid state when there is enhanced chain mobility along the c‐axis of a unit cell. The disentangled state is maintained in the melt over a period of time, invoking implications in polymer rheology. This approach is applicable to polymers in general. The homogeneous fully sintered UHMW‐PE, obtained for the first time, shows a considerable decrease in oxygen permeability, and increase in toughness and fatigue resistance. Such homogeneous products of UHMW‐PE are of beneficial in highly demanding applications, especially in knee‐prosthesis, where the polymer is used as an inlay between the human bone and a metal or ceramic part, which slides against the polyethylene component during normal gait.

Phase diagram for the extended chain crystals.     

Crystalline and Conductive Poly(3‐hexylthiophene) Fibers

Intrinsically conducting polymer fibers are prepared from P3HT by melt spinning. High crystallinity is achieved by drawing the fibers after the spinning process, applying a draw ratio of 1:2. DSC and XRD measurements confirm the continuous increase of crystalline phases with drawing. For comparison, poly(ethylene terephthalate) fibers are coated with P3HT and drawn as well. Again, the drawing of the coated fiber results in a significant increase in crystallinity of the P3HT coating. The high amount of crystalline phases is associated with a dramatic increase in conductivity (350 S · cm^?1) after doping with FeCl₃ in nitromethane.

     

Study of the Effects of Gamma Irradiation on the Structure and Physical Properties of Low Density Polyethylene Films Containing Hindered Amine Stabilizers

The effect of gamma‐irradiation on the structure, rheology, and mechanical properties of low density polyethylene (LDPE) films containing some new hindered amine stabilizers (HAS) has been investigated and the results obtained were compared to additive free samples. The HAS used involved various structures such as an alkoxyamine, a polymer bound HAS and a HAS modified with siloxane; these are commercially known as Tinuvin 123, Sanduvor PR 31 and Uvasil 299, respectively. It was found that the carbonyl index values measured by FTIR spectroscopy increased linearly with the radiation dose for all the samples studied, however this increase was less pronounced for the stabilized samples. The formation rates of carbonyls followed the order LDPE > LDPE/Uvasil 299 > LDPE/PR 31 > LDPE/Tinuvin 123. The second order derivative UV analysis showed the formation of vinyl groups in the irradiated samples at higher doses (812 kGy), while vinylidene groups were detected only in the films stabilized with PR 31 and Tinuvin 123. The curves of the melt flow rate (MFR) exhibited a fast increase for the unstabilized sample after 67 kGy, indicating the occurrence of chain scission. The stabilized samples on the other hand showed an evident increase in MFR from almost 300 kGy. The contribution of different HAS for the durability of LDPE films under γ rays was evaluated by determining the half‐value‐dose, which is related to the radiation resistance of the material. The results indicated that the presence of HAS in LDPE films improves the half‐value‐dose of those stabilized with Tinuvin 123 by 2.5 times against 2.4 and 2 for PR 31 and Uvasil 299, respectively. These data correlate well with the results obtained by FTIR and MFR measurements. Finally, the higher efficiency of Tinuvin 123 could be assigned to its appropriate oxidation state to enter the stabilization mechanism directly.

An example of the new HAS.     

Crystallization Kinetics and Hydrophilicity Improvement of Biodegradable Poly(butylene succinate) in its Miscible Blends with Poly(ethylene oxide)

The spherulitic morphology and growth, overall isothermal crystallization kinetics and hydrophilicity of PBSU were investigated by POM, DSC and WCA measurements in its miscible blends with PEO. The Hoffman‐Lauritzen equation was employed to analyze the spherulitic growth rates of neat and blended PBSU, which show a crystallization regime transition between regime II and III. The overall crystallization rates of PBSU decreased with increasing crystallization temperature, regardless of blend composition, while the crystallization mechanism does not change. A significant improvement in the hydrophilicity of PBSU can be achieved by blending with different weight fractions of PEO, which may be essential for the practical application of PBSU/PEO blends.