Zhikai Zhong

Phase behaviour and mechanical properties of epoxy resin containing phenolphthalein poly(ether ether ketone)

Abstract Blends of bisphenol-A-type epoxy resin(ER) and phenolphthalein poly(ether ether ketone) (PEK-C) cured with 4,4′-diaminodiphenylmethane (DDM) were studied using differential scanning calorimetry (DSC), dynamic mechanical analysis (DMA) and scanning electron microscopy (SEM). The phase behaviour of the DDM-cured ER/PEK-C blends was greatly dependent on the curing condition and was affected by both the thermodynamic and kinetic factors. The homogeneous DDM-cured ER/PEK-C blends were obtained. The studies of DSC and Fourier-transform infrared (FTi.r.) spectroscopy indicate that there existed some unreacted oxirane rings of ER in the blends, and the curing reaction was incomplete even though the samples of the blends were further post-cured at 250°C. Mechanical measurements show that incorporation of PEK-C slightly decreased both the fracture toughness (KIC and GIC) and the flexural properties, presumably due to the reduced cross-link density of the epoxy network. SEM observation of the surfaces of fracture mechanical measurement specimens indicates the nature of brittle fracture for the plain ER and the blends.

Miscibility and morphology of thermosetting polymer blends of novolac resin with poly(ethylene oxide)

Abstract Polymer blends of novolac resin and poly(ethylene oxide) (PEO) were prepared by solution casting from N, N -dimethylformamide (DNIF). The miscibility and morphology of the blends before and after curing were investigated by optical microscopy differential scanning calorimetry (d.s.c.) and Fourier transform infrared ( FT i.r.) spectroscopy. It was found that PEO is miscible with uncured novolac over the entire composition range, as shown by the existence of a single composition-dependence glass transition temperature (T g ). FT i.r. studies revealed that hydrogen bonding interactions exist between the hydroxyl groups of novolac and the ether oxygens of PEO. The relative amount and the average strength of the hydrogen bonds in the blends were higher than those in the pure novolac resin. The curing with 15 wt% hexamine (HMTA) (relative to novolac content) resulted in the disappearance of a detectable T g in both the neat novolac and the novolac-rich blends, due to the reduced mobility of the novolac chain segments. An analysis of the reduction in T m and crystallization rate with increasing novolac content revealed that the HMTA-cured blends remained completely miscible. After curing with HMTA, considerable hydrogen bonding interaction between the components still existed, which is the driving force for the miscibility of the HMTA-cured blends. The relative amount and the average strength of hydrogen bonds in the cured blends were lower than those in the uncured blends.

The miscibility and morphology of hexamine cross-linked novolac/poly(ϵ-caprolactone) blends

Abstract The miscibility and morphology of novolac/poly(ϵ-caprolactone) (PCL) blends before and after curing were investigated by optical microscopy, differential scanning calorimetry (d.s.c.) and FT i.r. It was found that PCL is miscible with uncured novolac resin, as shown by the existence of a single glass transition temperature (Tg) in each blend. FT i.r. studies revealed that hydrogen bonding interaction in novolac/PCL blend occurs between the hydroxyl groups of novolac and the carbonyl groups of PCL, which is responsible for the miscibility of the novolac/PCL blends. However, remarkable changes occurred after the novolac/PCL blends were cured with hexamine (HMTA), which can be considered to be due to the dramatic changes in chemical and physical nature of novolac resin during the cross-linking. Phase separation in the initially miscible novolac/PCL blends occurred after curing with 15 wt% HMTA (relative to novolac content). The phase structures of the cured blends show composition dependence. The cured novolac/PCL blends with novolac content up to 70 wt% were observed to be partially miscible, whereas the 90 10 cured novolac/PCL blend was found to be miscible. The curing reduces the intermolecular hydrogen-bonding significantly, but there still exists a considerable amount of residual intermolecular hydrogen bond in the cured blends with its strength much lower than that in the uncured blends. The morphology of the novolac/PCL blends was remarkably affected by curing. The curing results in the disappearing of the Tg behaviour of novolac, owing to less mobility of the novolac chain segments.

Miscibility and cure kinetics of nylon/epoxy resin reactive blends

The miscibility, phase behavior and cure kinetics of the reactive blends of an alcohol-soluble nylon with an epoxy resin, i.e. diglycidyl ether of bisphenol A (DGEBA), were studied by differential scanning calorimetry (d.s.c.) and Fourier transform infra-red spectroscopy (FTi.r.). Differential scanning calorimetry (d.s.c.) studies showed that all the uncured nylon/DGEBA blends were crystallizable and exhibited two glass transition temperatures (Tgs). The lower Tg is independent of composition and is due to the glass transition of DGEBA phase. The higher Tg varies with composition and is attributable to the glass transition of the nylon-rich phase. Nylon is partially miscible with DGEBA, and the extent of miscibility is dependent on the blend composition. Nylon and DGEBA in all the uncured blends can react with each other above 200°C. The curing reaction of nylon with DGEBA is dependent on the blend composition. The nucleophilic attack on oxirane ring by amide nitrogen of nylon is dominant curing reaction in low DGEBA compositions, and another type of curing reaction with relatively large activation energy and frequency factor also occurred which becomes dominant when the DGEBA content reaches 63 wt% or more. FTi.r. studies revealed three does exist two types of reactions during curing of nylon with DGEBA. All the cured nylon/DGEBA blends show a composition-independent Tg, which is the glass transition of cured nylon-DGEBA network. All other blends are uncrystallizable after curing except for the 9010 and 8020 nylon/DGEBA blends. The curing greatly destroyed the crystallinity of the blends.

Crosslinkable interpolymer complexes of novolac resin and poly(ethylene oxide)

Crosslinkable interpolymer complexes of novolac resin and poly(ethylene oxide) (PEO) were prepared by mutual mixing ethanol solutions of novolac and PEO. Fourier transform infrared (FTIR) studies revealed that the driving force for the formation of novolac/PEO complex is hydrogen bonding interaction between the hydroxyl groups of novolac and the ether oxygens of PEO. The morphology and thermal properties of the complexes before and after curing were investigated by optical microscopy and differential scanning calorimetry (DSC). It was found that the uncured novolac/PEO complexes had a single composition-dependent glass transition temperature (Tg). The curing with 15 wt % hexamine (HMTA) (relative to novolac content) resulted in disappearing of Tg behaviour for both the neat novolac and the novolac-rich complexes, owing to less mobility of the novolac chain segments. The melting temperature (Tm) and crystallization rate of the HMTA-cured novolac/PEO complexes decreased with increasing novolac content, and no Tm was observed for the cured complexes with PEO content less than 50%.

Miscibility, phase behavior, and mechanical properties of ternary blends of poly(vinyl chloride)/polystyrene/chlorinated polyethylene-graft-polystyrene

The effectiveness of chlorinated polyethylene-graft-polystyrene (CPE-g-PS) as a polymeric compatibilizer for immiscible poly(vinyl chloride)/polystyrene (PVC/PS) blends was investigated. The miscibility, phase behavior, and mechanical properties were studied using differential scanning calorimetry (DSC), dynamic mechanical analysis (DMA), Izod impact tests, tensile tests, and scanning electron microscopy (SEM). DSC and DMA studies showed that PVC is immiscible with chlorinated polyethylene (CPE) in CPE-g-PS, whereas the PS homopolymer is miscible with PS in CPE-g-PS. The PVC/PS/CPE-g-PS ternary blends exhibit a three-phase structure: PVC phase, CPE phase, and PS phase that consisted of a PS homopolymer and PS in CPE-g-PS. The mechanical properties showed that CPE-g-PS interacts well with both PVC and PS and can be used as a polymeric compatibilizer for PVC/PS blends. CPE-g-PS can also be used as an impact modifier for both PVC and PS. SEM observations confirmed, after the addition of CPE-g-PS, improvement of the interfacial adhesion between the phases of the PVC/PS blends.

Crystallization kinetics of crosslinkable polymer complexes of novolac resin and poly(ethylene oxide)

Results of a study on the isothermal crystallization and thermal behavior of both uncured and hexamine-cured novolac/poly(ethylene oxide) (PEO) complexes are reported. The crystallization behavior of PEO in complexes is strongly influenced by factors such as composition, crystallization temperature, complexation, and crosslinking. The time dependence of the relative degree of crystallinity at high conversion deviated from the Avrami equation. The cured complexes exhibited an obvious two-stage crystallization (primary crystallization and crystal perfection), and this was more evident at higher crystallization temperature and high PEO-content. The addition of a noncrystallizable component into PEO caused a depression of both the overall crystallization rate and the melting temperature. In general, complexation and curing resulted in an increase in the overall crystallization rate. Complexation and curing are beneficial to the nucleation of PEO. Additionally, curing led to changes of the nucleation mechanism. Experimental data on the overall kinetic rate constant Kn were analyzed by means of the nucleation and crystal growth theory. For uncured complexes, the surface free energy of folding, σe, increased with increasing novolac content, whereas for cured complexes, σe displayed a maximum with the variation of composition.

Crystallization kinetics of miscible thermosetting polymer blends of novolac resin and poly(ethylene oxide)

Abstract Results of an investigation of isothermal crystallization and melting behavior of both uncured and hexamine-cured novolac/poly(ethylene oxide) (PEO) blends were reported. The crystallization behavior of PEO in blends is strongly influenced by factors such as composition, crystallization temperature, and cross-linking. The time dependence of the relative degree of crystallinity deviated from the Avrami equation at high conversion. The addition of non-crystalline component into PEO caused a depression in both the overall crystallization rate and the melting temperature. The influence of curing on the crystallization and melting behavior of PEO is rather complicated. In general, curing led to increase of the overall crystallization rate of the blends, and enhanced the nucleation rate of PEO. The crystallization mechanism of PEO changed after curing. Curing also resulted in relatively slow depression of equilibrium melting point, and reduced the stability of PEO crystals in the blends. Experimental data on the overall kinetic rate constant Kn were analyzed according to the nucleation and growth theory. The surface free energy of folding σ e showed an increase with increase of novolac content for the uncured blends, whereas σ e displayed a maximum at 90/10 PEO/novolac composition for the cured blends.

Miscibility and interchange reactions in blends of bisphenol-A-type epoxy resin and poly(ethylene terephthalate)

Blends of diglycidyl ether of bisphenol A (DGEBA) and poly(ethylene terephthalate) (PET) were prepared by solution casting from 1,1,2,2-tetrachloroethane. The miscibility and interchange reactions in DGEBA-PET blends were studied by differential scanning calorimetry (DSC) and optical microscopy. PET was found to be miscible with DGEBA, as revealed by the existence of a single composition-dependence glass transition temperature (T g ). Interchange reactions between DGEBA and PET components in the blends at elevated temperatures were proven by appearance of the enhanced glass transition temperatures and the marked decrease in the crystallinity of PET. These results are attributed to the formation of copolymers based on the blend components due to interchange reactions. The morphological observations confirmed that there existed interchange reactions between DGEBA and PET. There also existed a self-crosslinking reaction among the DGEBA molecules.

A polymer of bisphenol A and bisphenol A diglycidyl ether and its blends with poly(styrene-co-acrylonitrile): In situ polymerization preparation, morphology, and mechanical properties

The poly(hydroxy ether of bisphenol A)-based blends containing poly(acrylontrile-co-styrene) (SAN) were prepared through in situ polymerization, i.e., the melt polymerization between the diglycidy ether of bisphenol A (DGEBA) and bisphenol A in the presence of poly(acrylontrile-co-styrene) (SAN). The polymerization reaction started from the initial homogeneous ternary mixture of SAN/DGEBA/bisphenol A, and the phenoxy/SAN blends with SAN content up to 20 wt % were obtained. Both the solubility behavior and Fourier transform infrared (FTIR) spectroscopy studies demonstrate that no intercomponent reaction occurred in the reactive blend system. Differential scanning calorimetry (DSC), dynamic mechanical analysis (DMA), and scanning electronic microscopy (SEM) were employed to characterize the phase structure of the as-polymerized blends. All the blends display the separate glass transition temperatures (Tgs); i.e., the blends were phase-separated. The morphological observation showed that all the blends exhibited well-distributed phase-separated morphology. For the blends with SAN content less than 15 wt %, very fine SAN spherical particles (1–3 μmm in diameter) were uniformly dispersed in a continuous matrix of phenoxy and the fine morphology was formed through phase separation induced by polymerization. Mechanical tests show that the blends containing 5–15 wt % SAN displayed a substantial improvement of tensile properties and Izod impact strength, which were in marked contrast to those of the materials prepared via conventional methods.