NMR analysis of poly(ethylene naphthalate) + poly(butylene terephthalate) blends

Melt blends of poly (butylene terephthalate) (PBT) and poly (ethylene naphthalate) (PEN) with 30, 40, 50, 60 and 70 wt% PEN were prepared using a single screw extruder and injection moulding machine. ¹³C and ¹H nuclear magnetic resonance (NMR) spectra were obtained with a Bruker DRX-400 instrument, on solutions prepared by dissolving samples of the homopolymers and each blend in deuterated trifluoroacetic acid + chloroform mixtures (1:1 by volume). The absence of new signals in ¹H and ¹³C spectra, that would be expected to result from transesterification reactions in the PBT + PEN blend system, provides convincing evidence that such reactions do not occur in these blends under the melt processing conditions that were used. In the light of published work on solid-state NMR studies of these and related blend systems, and our observations of partial miscibility with a very small domain size, together with substantial enhancement of the mechanical properties of PBT by blending with PEN, we conclude that the improvement in mechanical properties arises from molecular scale mixing of the homopolymers and strong but non-covalent bonding interactions over the very large interfacial area between the PBT-rich and PEN-rich phases.     

Viscoelastic properties of poly(butylene terephthalate)/poly(ethylene naphthalate) blends

Melt blends of poly(butylene terephalate) (PBT) and poly(ethylene naphthalate) (PEN) with 30 and 60 wt% PEN were prepared using a single screw extruder and an injection moulding machine. Stress relaxation tests for the specimens of PBT/PEN blends and the homopolymers were carried out using an Instron testing machine in an Instron environmental chamber. The Taguchi method of experimental design analysed how different levels of temperature, PEN content and initial stress affected the relaxation behaviour of PBT/PEN blends and homopolymers. From the response tables and analyses of main and interaction effects, it was shown that the most significant factor was temperature, followed by PEN content and then the initial stress. Consequently, high temperature, low PEN content and high initial stress speeded up stress relaxation rate of specimens. Interaction effects between factors were insignificant. To fit the relaxation curves of the PBT/PEN blends and the homopolymers at different temperatures, PEN contents and the initial stresses, four different equations were attempted with Matlab™, which determined the coefficients of these functions using the experimental data of stress change with time. The simulated curves from the most suitable function among them were shown using the calculated coefficients to predict the relaxation behaviour of PBT/PEN blends (50% PEN) at temperatures of 30 and 60°C with an initial stress of 7 MPa.     

Thermal stability and thermal degradation kinetics of poly(ethylene 2,6-naphthalate)/poly(trimethylene terephthalate) blends

The kinetics of thermal degradation of poly(ethylene 2,6-naphthalate)/poly(trimethylene terephthalate) (PEN/PTT) blends with different weight ratio were investigated by thermogravimetry analysis from ambient temperature to 800 °C in flowing nitrogen. The kinetic parameters, including the activation energy E _a, the reaction order n, and the pre-exponential factor ln(Z), of the degradation of the PEN/PTT blends were evaluated by three single heating rate methods and advanced isoconversional method developed by Vyazovkin. The three single heating rate methods used in this work include Friedman, Freeman–Carroll, and Chang method. The effects of the heating rate, the calculation methods, and the content of the PEN component on the thermal stability and degradation kinetic parameters of the PEN/PTT blends were systematically discussed. The PEN/PTT blends which degraded in two distinct stages were stable under nitrogen, also, the maximum rate of weight loss increased linearly with increasing of heating rate and decreased with increasing of PEN content. The obtained kinetics data suggested that the introduction of PEN component increased the activation energy, enhanced the stability of the blend system, and affected the process of degradation of PEN/PTT blend.     

Miscibility and melting properties of poly(ethylene 2,6-naphthalate)/poly(trimethylene terephthalate) blends

The miscibility and melting properties of binary crystalline blends of poly(ethylene 2,6-naphthalate)/poly(trimethylene terephthalate) (PEN/PTT) have been investigated with differential scanning calorimetry (DSC). The glass transition and cold crystallization behaviors indicated that in PEN/PTT blends, there are two different amorphous phases and the PEN/PTT blends are immiscible in the amorphous state. The polymer–polymer interaction parameter, , calculated from equilibrium melting temperature depression of the PEN component was −1.791 × 10⁻⁵ (300 °C), revealing miscibility of PEN/PTT blends in the melt state.     

Tensile behaviour of blends of poly(vinylidene fluoride) with poly(methyl methacrylate)

Blends of poly(vinylidene fluoride) (PVF₂) and poly(methyl methacrylate) (PMMA) were prepared over a wide concentration range and tested in tension at the same relative temperature below the glass transition. Testing was performed at strain rates ranging from 10 to 0.01 min^–1 at test temperatures fromT _g-40 toT _g-10. By normalizing the test temperature to fixed increments belowT _g, blends and homopolymers can be compared on the basis of PVF₂ and PMMA composition and crystallinity. In nearly all blends, under conditions favouring disentanglement, (decrease in strain rate, or increase in test temperature), the yield stress and drawing stress decreased while the breaking strain increased. For materials with about the same degree of crystallinity, those with a higher proportion of amorphous PVF₂ exhibited brittle-like behaviour as a result of interlamellar tie molecules. In the semicrystalline blends, yield stress remains high as the test temperature approachesT _g, whereas in the amorphous blends the yield stress falls to zero nearT _g. Results of physical ageing support the role of interlamellar ties which cause semicrystalline blends to exhibit ageing at temperatures aboveT _g.     

Super-tough poly(butylene terephthalate) based blends by modification with core-shell structured polyacrylic nanoparticles

Core-shell structured polyacrylic nanoparticles (named CSPN) impact modifiers consisting of a rubbery poly(n-butyl acrylate) core and a rigid poly(methyl methacrylate) shell with a size of about 352 nm were synthesized by seed emulsion polymerization. The CSPN modifier with core-shell weight ratio 80/20 was used to toughen poly(butylene terephthalate) (PBT) by melt blending. With an increase in CSPN content, the impact strength and the elongation at break of PBT/CSPN blends increased significantly compared with those of PBT; however, the tensile strength decreased. It was found that the polymerization had a very high instantaneous conversion (> 93%) and overall conversion (99%). The core-shell structure of CSPN was examined by means of transmission electron microscope. Scanning electron microscope was used to observe the morphology of CSPN particle and fractured surfaces of the blends. The dynamic mechanical analyses of PBT/CSPN blends showed two merged transition peaks of PBT matrix, with the presence of CSPN modifier, which was responsible for the improvement of PBT toughness. The results indicated that the notched impact strength of PBT/CSPN blend with a weight ratio of 80/20 was 8.61 times greater than that of pure PBT where the brittle-ductile transition point appeared.     

Fracture toughness and fracture mechanisms of PBT/PC/IM blends: Part V Effect of PBT-PC interfacial strength on the fracture and tensile properties of the PBT/PC blends

To investigate the effect of PBT-PC interfacial strength on the fracture toughness and toughening mechanisms of the PBT/PC system, a series of PBT/PC blends with different content of in situ formed PBT-PC copolymers were made by melt blending. The in situ copolymer was separately prepared via reactive blending of the PBT and PC in the presence of a transesterification catalyst in a twin-screw extruder for a few minutes. The reactive extrudate (RE) was studied using a DSC and the existence of the PBT-PC copolymer in the RE was confirmed. Microstructure characterizations of the PBT/PC/RE blends revealed that the domain sizes of the PBT and PC decrease and the PBT-PC interfacial strength increases with the RE content. Compared with the PBT/PC blend, all the PBT/PC/RE blends have higher yield strength, elongation at break as well as tensile modulus. The quasi-static fracture tests show that fracture toughness of the blends increases with the RE content. Since the highest toughness was obtained with the blend having the highest RE content (7.5%), it is not certain at this stage whether adding more than 7.5% RE will further improve the fracture toughness. The impact toughness of the PBT/PC/RE blends was found to decrease with the increase of the PBT-PC interfacial strength, which confirms the failure mechanisms proposed in the Part-4 of this series.     

Crystallisation and miscibility of poly(ethylene oxide)/poly(vinyl chloride) blends

Isothermal crystallisation of blends of Poly(ethylene oxide) and Poly(vinyl chloride), PEO/PVC, was analysed by differential scanning calorimetry (DSC). The influence of the amorphous polymer, PVC, on crystallisation rate of PEO was investigated using pure PEO as reference. Pure PEO and PEO/PVC blends were submitted to different crystallisation temperatures (from 40 to 58°C) and crystallisation times (from 1 to 72 h). Using the Hoffman-Weeks plot procedure, the equilibrium melting temperature, T _m°, was determined for pure PEO and for PEO/PVC blends with compositions (in wt%): 90/10, 80/20, 70/30, 60/40, 50/50, 40/60, 30/70 and 20/80. The lamellar thickness factor of PEO crystals for pure PEO and for the blends showed a strong decrease when the PVC content was higher than 60 wt%. A small depression in T _m° was verified as the composition of PVC was increased. From the depression in T _m° the polymer-polymer interaction parameter, ₁₂, was evaluated using the Nishi-Wang equation. The results indicate that the miscibility between PEO and PVC in the molten state depends on the blend composition. The crystallisation rate also depends on the blend composition: the richer in PVC is the blend, the slower the crystallisation process.     

Miscibility, morphology and fracture toughness of tetrafunctional epoxy resin/poly (styrene-co-acrylonitrile) blends

Poly(styrene-co-acrylonitrile) (SAN) was found to be miscible with the tetraglycidylether of 4,4'-diaminodiphenylmethane (TGDDM), as shown by the existence of a single glass transition temperature (T _g) over the whole composition range. However, SAN was found to be immiscible with the 4,4-diaminodiphenylmethane (DDM)-cured TGDDM. Dynamic mechanical analysis (DMA) shows that the DDM-cured TGDDM/SAN blends have two T _gs. A scanning electron microscopy (SEM) study revealed that all the DDM-cured TGDDM/SAN blends have a two-phase structure. The fracture toughness K _IC of the blends increased with SAN content and showed a maximum at 10 wt% SAN content, followed by a dramatic decrease for the cured blends containing 15 wt% SAN or more. The SEM investigation of the K _IC fracture surfaces indicated that the toughening effect of the SAN-modified epoxy resin was greatly dependent on the morphological structures.     

Mechanical properties and structure of glassy and semicrystalline random copolymers of poly(ethylene terephthalate) and poly(ethylene naphthalene-2,6-dicarboxilate)

The microhardness,H, of random copolymers of poly(ethylene terephthalate) (PET) and poly(ethylene naphthalene-2,6-dicarboxilate) (PEN) was determined over a wide range of compositions. It is shown that microhardness of the materials is strongly affected by the composition. The mechanical property,H, of the quenched amorphous copolyester films is discussed in terms of a simple model given by the additivity values of the single componentsH _a ^PET andH _a ^PEN . In materials containing up to 30% PEN, crystals of PET are found after annealing at temperatures 10 °C below their melting points. In materials containing 80% PEN, after annealing at about 20 °C below the melting point, crystals of PEN are formed. The observed deviation ofH for the crystallized films from the additive behaviour of the single components can be quantitatively related to two factors: the changes occurring in the crystallinity value and in the thickness of PET and PEN crystals.     

Structure formation and miscibility of sheets from PBT and LCP blends

Sheets from blends containing poly(butylene terephthalate) (PBT) and liquid crystalline polymer (LCP) were prepared using a twin-screw extruder. The LCP used is a copolymer composed of 20 mol % ethylene terephalate (PET) and 80 mol % p-hydroxybenzoic acid (PHB). Thermal behavior, viscoelastic properties, and structure of the sheets of various compositions were investigated by using differential scanning calorimetry (DSC), dynamic mechanical analysis (DMA), microwave orientation analysis (MOA), and wide angle x-ray diffraction (WAXD). X-ray diffractograms of extruded sheets from PBT, LCP, and their blends show a high degree of orientation along extrusion direction. The orientation is mainly due to the high crystallization rate of PBT, although crystallization and orientation of PBT in the PBT and LCP blends could also be induced by adding LCP. In the PBT and LCP blends, the thermal properties of the constituents are slightly changed indicating that PBT and LCP are partially miscible. DSC measurements show that as the amount of LCP added to the blend increased, the melting point T _m of PBT in the blends decreased. The single glass transition temperature T _g for the PBT and LCP was observed by DMA. Furthermore, no evidence of transesterification in PBT and LCP blends was observed by WAXD.     

Poly(ether ether ketone) with pendent methyl groups as a toughening agent for amine cured DGEBA epoxy resin

A diglycidyl ether of bisphenol-A (DGEBA) epoxy resin was modified with poly(ether ether ketone) with pendent methyl groups (PEEKM). PEEKM was synthesised from methyl hydroquinone and 4,4′-difluorobenzophenone and characterised. Blends of epoxy resin and PEEKM were prepared by melt blending. The blends were transparent in the uncured state and gave single composition dependent T _g. The T _g-composition behaviour of the uncured blends has been studied using Gordon–Taylor, Kelley–Bueche and Fox equations. The scanning electron micrographs of extracted fracture surfaces revealed that reaction induced phase separation occurred in the blends. Cocontinuous morphology was obtained in blends containing 15 phr PEEKM. Two glass transition peaks corresponding to epoxy rich and thermoplastic rich phases were observed in the dynamic mechanical spectrum of the blends. The crosslink density of the blends calculated from dynamic mechanical analysis was less than that of unmodified epoxy resin. The tensile strength, flexural strength and modulus were comparable to that of the unmodified epoxy resin. It was found from fracture toughness measurements that PEEKM is an effective toughener for DDS cured epoxy resin. Fifteen phr PEEKM having cocontinuous morphology exhibited maximum increase in fracture toughness. The increase in fracture toughness was due to crack path deflection, crack pinning, crack bridging by dispersed PEEKM and local plastic deformation of the matrix. The exceptional increase in fracture toughness of 15 phr blend was attributed to the cocontinuous morphology of the blend. Finally it was observed that the thermal stability of epoxy resin was not affected by the addition of PEEKM.     

Design,synthesis and physical properties of poly(styrene-butadiene-styrene)/poly(thiourea-azo-sulfone) blends

A new aromatic azo-polymer, poly(thiourea-azo-sulfone), has been synthesized using 1-(4-thiocarbamoylaminophenylsulfonylphenyl)thiourea and diazonium salt solution. Conducting and thermally stable rubbery blends of poly(styrene-block-butadiene-block-styrene) (SBS) triblock copolymer and poly(thiourea-azo-sulfone) (PTAS) were produced by solution blending technique. PTAS possessed fine solubility in polar solvents and high molar mass 63 × 10₃ g moL^?1. Microscopic analysis on SBS/PTAS blends revealed good adhesion between the two polymers without macro phase separation. Electrical conductivity measurement recommended that blending of SBS with 60% PTAS was sufficiently conducting 1.43 S cm^?1. A relationship between PTAS loading and thermal stability of blends was observed. With the increasing PTAS content, 10% gravimetric loss was increased from 481 to 497 °C, while glass transition improved from 123 to 136 °C (better than neat SBS but lower than PTAS). The blends also established higher tensile strength (52.40–59.96 MPa) relative to SBS. Fine balance of properties renders new SBS/PTAS, potential engineering plastics for a number of aerospace relevance.     

Effect of core–shell structured modifier ACR on ASA/SAN/ACR ternary blends

In this study, acrylonitrile–styrene–acrylic terpolymer/styrene–acrylonitrile copolymer/acrylic resin (ASA/SAN/ACR) ternary blends with different compositions were prepared by melting blending. Properties of the ternary blends were studied by differential scanning calorimetry, heat distortion temperature (HDT), Fourier transform infrared (FTIR) spectra, melt flow rate (MFR), mechanical properties, and scanning electron microscopy (SEM). The blends showed two T _gs at about −48 and 109 °C. FTIR analyses showed no strong interactions between the characteristic groups existed in the prepared blends. No obvious phase separation observed in SEM images indicated good compatibility in the blend system. With respect to mechanical properties and processability, the addition of ACR not only led to the improvement of impact strength and elongation at break, but also the decline of tensile strength, flexural properties, hardness, and MFR. Furthermore, heat resistance of ASA/SAN (70/30) binary blends decreased with the addition of ACR, but the HDT of ASA/SAN (30/70) almost remain unchanged.     

Nanostructure of atmospheric and high-pressure crystallised poly(ethylene-2,6-naphthalate

Poly(ethylene-2,6-naphthalate) (PEN) was crystallized from the glassy state at atmospheric pressure (beyond the end of primary crystallization) and from the melt at high pressure. The structure was characterized using small-angle X-ray scattering (SAXS), wide-angle X-ray scattering (WAXS), differential scanning calorimetry (DSC) and density measurements. The SAXS patterns were analysed using the interface distribution function (IDF) method. For the materials prepared at ambient pressure the crystallinity inside the layer stacks remains nearly constant during the secondary crystallization process. On the other hand, the volume filled with the stacks increases as a function of crystallization temperature (T _c) and time (t _c). For T _c > 200°C secondary crystallisation goes along with a dynamic rearrangement of the primary stacks, as concluded from variations of the layer thickness distributions in the SAXS data. For T _c < 200°C primary lamellae are stable, and both insertion of new crystal lamellae into existing stacks and generation of additional stacks is found. In contrast to PET, two different kinds of layer stacks are not observed in the PEN nano-composites. Materials prepared at 400 MPa exhibit high roughness of the crystalline domain surfaces. Depending on T _c there is a continuous transformation from the to the -crystal modification, but hardly any change of the long period. Crystal thickness increases, both at the expense of the amorphous thickness and of the volume filled with lamellar stacks. The structure of samples showing two melting peaks is discussed in terms of a dual lamellar contribution of correlated and uncorrelated nano-crystallites, respectively.     

Biodegradation of porous versus non-porous poly(L-lactic acid) films

The influence of porosity on the degradation rate of poly(L-lactic acid) (PLLA) films was investigated in vitro and in vivo. Non-porous, porous and combi (porous with a non-porous layer) PLLA films were used. Changes in Mw, Mn, polydispersity (Mw/Mn) ratio, melting temperature (T _m), heat of fusion, tensile strength, E-modulus, mass and the remaining surface area of cross-sections of the PLLA films were measured. In general, during the degradation process, the porous film has the highest Mw, Mn, Mw/Mn ratio and T _m, while the non-porous film has the lowest. In contrast, the highest heat of fusion values were observed for the non-porous film, indicating the presence of relatively smaller molecules forming crystalline domains more easily. The tensile strength and E-modulus of the non-porous film decrease faster than those of the porous and the combi film. None of the three types of films showed massive mass loss in vitro nor a significant decrease in remaining polymer surface area in light microscopical sections in vitro and in vivo. Heavy surface erosion of the non-porous layer of the combi film was observed after 180 days, turning the combi film into a porous film. This is also indicated by the changes in tensile strength, Mw, Mw/Mn, T _m and heat of fusion as a function of time. It is concluded that non-porous PLLA degrades faster than porous PLLA. Thus, in our model, porosity is an important determinant of the degradation rate of PLLA films.     

Miscible blends from rigid poly(vinyl chloride) and epoxidized natural rubber

Miscible blends of rigid poly(vinyl chloride), PVC, and epoxidized natural rubber (ENR) having 50 mol % epoxidation level, are prepared in a Brabender Plasticorder by the melt-mixing technique. Changes in Brabender torque and temperature, density, dynamic mechanical properties and DSC thermograms of the samples are studied as a function of blend composition. The PVC-ENR blends behave as a compatible system as is evident from the singleT _g observed both in dynamic mechanical analysis (DMA) and differential scanning calorimetry (DSC). The moderate level broadening of theT _g zone in blends is due to microinhomogeneity, which may arise from the particle structures of PVC perturbing the molecular level mixing of PVC and ENR. Scanning electron microscopic studies were conducted on nitric acid-etched samples and the results showed continuous structures of blend components as well as the occurrence of solvent-induced cracks in high PVC blends.     

The effect of crystalline morphology of poly (butylene terephthalate) phases on toughening of poly(butylene terephthalate)/epoxy blends

In an effort to investigate the effect of the crystalline morphology of a poly(butylene terephthalate) (PBT) phase on the toughening of PBT/epoxy blends, the blends, having different degrees of perfectness of the PBT crystalline phase, were prepared by blending PBT and epoxy at various temperatures ranging from 200 to 240 °C. As the blending temperature decreases, the degree of perfectness of the PBT crystalline phase increases as a result of the increase of crystal growth rate. For PBT/epoxy blends, the change in crystalline morphology induced by processing may be the most important cause for the dependency of the fracture energy on blending temperatures. It has been found that PBT phases with a well-developed Maltese cross are most effective for epoxy toughening. This dependency reveals the occurrence of a phase transformation toughening mechanism. Also, the higher relative enhancement of fracture energy of a higher molecular weight epoxy system is further indirect evidence for a phase transformation toughening mechanism. Some other toughening mechanisms observed from the fracture surfaces, such as crack bifurcation, crack bridging, and ductile fracture of PBT phases, have been found to also be affected by the blending temperatures.     

Enthalpy relaxation behaviour of metal-metal (Zr-Cu) amorphous alloys upon annealing

Anneal-induced enthalpy relaxation behaviour was examined calorimetrically for Zr_50-70Cu_50-30, Zr₇₀(Cu-Fe)₃₀ and Zr₇₀(Cu-Ni)₃₀ amorphous alloys. When the alloys annealed at temperatures belowT _g are heated, an excess endothermic reaction (enthalpy relaxation) occurs above the annealing temperatureT _a. The peak temperature of C _p,endo, evolves in a continuous manner with lnt _a. The magnitudes of C _p,endo and H _endo for Zr-Cu binary alloys increase gradually with risingT _a and then rapidly at temperatures just belowT _g, while their changes as a function ofT _a for the ternary alloys show a distinct two-stage splitting; a low-temperature one which peaks at aboutT _g — 150 K and a high-temperature peak just belowT _g. From the result that the addition of iron or nickel causes the two stage splitting of the C _p,endo (T _a), it was proposed that the low-temperature endothermic peak is attributed to local and medium range rearrangments of copper and iron or nickel atoms with weak bonding nature and the high-temperature reaction to the long-range co-operative regroupings of zirconium and copper, iron or nickel atoms which are composed of the skeleton structure in the metal-metal amorphous alloys. The mechanism for the appearance of the two-stage enthalpy relaxation was investigated by the concept of two-stage distributions of relaxation times proposed previously, and the distinct two-stage splitting was interpreted as arising from the distinctly distinguishable difference in the ease of atomic rearrangements between Cu-(Fe or Ni) and Zr-(Cu, Fe or Ni).     

Properties of pressure sensitive adhesive made of acrylic quaternary copolymers and their blends with vinyl chloride copolymers

Acrylic quaternary copolymers (AQC) were synthesized from copolymerization reaction of 2-ethylhexyl acrylate (2-EHA), n-butyl acrylate (BA), ethyl acrylate (EA) and vinyl acetate (VAc). The blends of AQC with poly(vinyl chloride-co-vinyl acetate) (PVCVAc) and with poly(vinyl chloride-co-vinyl propionate) (PVCVP) were prepared by solution blending. Pressure sensitive adhesive (PSA) properties of AQC and their blends were investigated. Glass transition temperature T _g and holding power of AQC decreases with increasing contents of 2-EHA and BA. Tackiness, however, increases with increasing the contents of 2-EHA and BA. Peel strength shows maximum value for the sample with 15 wt% of those monomers. Tackiness of blend systems is similar, but holding power begins to decrease at 15 wt% or higher PVCVAc contents in AQC+PVCVAc blends. On the other hand, holding power of AQC+PVCVP blends increases as the contents of PVCVP increases. Failure modes of the blend are adhesive except for blends with 5 wt% of PVCVP.