Fold Surface Free Energy Σe Research Articles

Influence of isotactic polypropylene grafted with styryl-group on the polymer crystallization behavior

4-Furfuryloxymethylstyrene (Sf) grafted isotactic polypropylene (iPP-g-Sf) was prepared by melt grafting reaction. The crystallization temperature of iPP after grafting increased to ∼130 °C. The isothermal and non-isothermal crystallization kinetics of iPP-g-Sf containing up to 1.50 mol% grafted Sf groups were compared with that of virgin iPP, and the isothermal and non-isothermal crystallization kinetics parameters of the polymers, including the fold surface free energy σe, the chain folding work q, and the crystallization activation energy ΔE, were calculated by Lauritzen-Hoffman theory and Kissinger method respectively. The results showed that iPP-g-Sf exhibited a unique self-nucleation phenomenon, which accelerating the crystallization rate of iPP and produced tiny crystal morphology than that for iPP. The introduction of only 0.23–1.50 mol% grafted Sf groups reduced the σe of the crystals by 44–57%. This might provide guidance for the design of polymer crystallization rate by controlling the molecular structures.

Crystallization behaviour of syndiotactic polystyrene and benzoylated syndiotactic polystyrene

The crystallization behaviour of syndiotactic polystyrene (sPS) and benzoylated sPS (BzsPS) was investigated by POM, DSC and XRD. The results suggest β form of sPS has higher equilibrium melting temperature Tm0 and the fold surface free energy σe than α form. With increasing benzoylation degree the growth rates and Tm0 of two forms decrease, but their Tm0 decrement is very close; the σe of β form more increases than that of α form, the formation of α is more favourable. Upon loading trace amount of α nucleating agent PTBBNa in samples the growth rate of two forms can be strictly compared in the same melting and crystallization temperature condition, the results reveal that the growth rate of β form is faster than that of α form in sPS and BzsPS-2%. Using supercooling degree ΔT and σe two parameters has explained the formation competition mechanism of α and β forms.

Crystallization of poly(ethylene oxide) with acetaminophen – A study on solubility, spherulitic growth, and morphology

A simple, sensitive, efficient, and novel method analyzing the number of spherulitic nuclei was proposed to estimate the solubility of a model drug acetaminophen (APAP) in poly(ethylene oxide) (PEO). At high crystallization temperature (323K), 10% APAP–PEO had the same low number of spherulitic nuclei as pure PEO, indicating that APAP and PEO were fully miscible. At low crystallization temperature (303K), the number of nuclei for 10% APAP–PEO was significantly higher, suggesting that APAP was oversaturated and therefore recrystallized and acted as a nucleating agent. Based on the results obtained, the solubility of APAP in PEO is possibly between the concentration of 0.1% and 1% at 303K. The spherulitic growth rate G of PEO was found to decrease with increasing APAP concentration, suggesting that APAP is most likely functioning as a chemical defect and is either rejected from or included in the PEO crystals during chain folding. APAP could possibly locate in the inter-spherulitic, inter-fibrillar, inter-lamellar, or intra-lamellar regions of PEO. At 323K, the morphology of 10% APAP–PEO is more dendritic than spherulitic with large unfilled space in between dendrites and spherulites, which is a sign of one or the combination of the four modes of segregation. An extensive spherulitic nucleation and growth kinetics study using the classical theoretical relationships, for example, the Hoffman–Lauritzen (HL) and Avrami theories, was conducted. Both microscopic and differential scanning calorimetric (DSC) analysis yielded similar values for the nucleation constant Kg as well as the fold surface free energy σe and work of chain folding q. The values of σe and q increased with APAP concentration, indicating that the chain folding of PEO was hindered by APAP.

Effect of multi-walled carbon nanotubes on crystallization behavior of poly(3-hydroxybutyrate-co-3-hydroxyvalerate)

The effect of multi-walled carbon nanotubes on the crystallization behavior of poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV) has been investigated. The results have shown that carbon nanotubes (CNTs) act as an effective heterogeneous nucleation agent, inducing an increase in crystallinity and crystallite sizes. Comparing with the double melting peaks in pure PHBV, there is only one peak in the melting curves of nanocomposites. The isothermal crystallization kinetics of PHBV and its nanocomposite containing 0.5% CNTs were examined based on Avrami equation, indicating that the crystallization half-time decreases while the overall crystallization rate k increases dramatically with CNTs addition. The spherulitic nucleation and growth kinetics were also discussed grounded on Lauritzen–Hoffman equation. It is found that there is a spherulitic growth rates (G) maximum within selected temperature range in our study. Also, the temperatures corresponding to G maximum shift to a high level with addition of CNTs. The parameters of the equilibrium melting temperature \( T_m^0 \), the nucleation parameter Kg, the lateral surface free energy σ, the fold surface free energy σe, and the work of chain folding q of PHBV and its composite containing 0.5% CNTs were all calculated. The reductions of Kg, σe and q values of nanocomposite are in agreement with the fact that the crystallization rate of PHBV increases greatly by addition of CNTs.

Non-isothermal crystallization kinetics of poly (lactic acid)/modified carbon black composite

A novel method was employed to modify the surface of carbon black (CB) by an organic small molecule in a Haake Rheomix mixer. Jeziorny equation, the Ozawa model and Mo equation were employed to describe the non-isothermal crystallization process of poly (lactic acid) (PLA), PLA/CB and PLA/modified carbon black (MCB) composites. It is found that the Ozawa model fail to describe the non-isothermal crystallization process for PLA and its composites, while Jeziorny equation and Mo’s theory provide a good fitting. The comparison of crystallization kinetics between PLA/MCB and PLA through Lauritzen–Hoffman model indicates that there appears a transition from regimes II to III in PLA and PLA/MCB. The fold surface free energy σe of PLA/MCB composite is higher than that of neat PLA, implying that the existence of nucleating agent is unfavorable for the regular folding of the molecule chain.

Effect of nucleating agents on crystallization kinetics of PET

Effects of three nucleating agents concluding talc, sodium benzoate (SB) and an ionomer (Ion., Na+) on crystal- lization of poly(ethylene terephthalate) (PET) were studied by differential scanning calorimetry (DSC) and polarized opti- cal microscope (POM), the parameters of crystallization kinetics were obtained through Avrami and Ozawa equations. The fold surface free energy σe of pure PET and PET/nucleating agent blends was calculated by Hoffman-Lauritzen theory. The results indicate that the three kinds of nucleating agents increase the crystallization rate constant through promoting their nucleating effect for PET crystallization, among which SB is the best one with the same content. The crystallization mode of PET might shift from three-dimensional growth to two-dimensional growth by the addition of the nucleating agents. The values of σe of PET/nucleating agent blends are much less than that of pure PET, and PET/SB (99:1) blend has the least value of σe (18.2 mJ/m2). The conclusion based on Hoffman theory is similar to the analysis by Avrami and Ozawa equa- tions.

Blends of polypropylene resins with a liquid crystalline polymer. I. Isothermal crystallization

AbstractThe isothermal crystallization kinetics of blends of different polypropylene (PP) resins and a liquid crystalline polymer (LCP) after two different melting conditions (200 and 290°C) were studied by DSC and polarized light optical microscopy. The resins were a homopolymer (hPP), a random copolymer with ethylene (cPP), and a maleic anhydride grafted PP (gPP). The LCP was Vectra A950, a random copolymer made of 75 mol % of 4‐hydroxybenzoic acid and 25 mol % of 2‐hydroxy,6‐naphthoic acid. It was observed that the overall crystallization rates of all the blends after melting at 200°C were higher than those after melting at 290°C. The LCP acted as a nucleating agent for all the PP resins; however, its nucleating effect was stronger for the hPP than for the cPP and gPP resins. After both melting conditions, an increase was observed in the overall crystallization rate of the hPP and gPP resins with the increase in the amount of LCP, but not in the cPP crystallization rate. The fold surface free energy σe of hPP and cPP in the blends decreased, but increased in the gPP blends. Finally, all the PP resins formed transcrystallites on the LCP domain surfaces. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 87: 916–930, 2003

Effect of isotacticity distribution on crystallization kinetics of polypropylene

AbstractThe crystallization kinetics of isotactic polypropylene (iPP) depends not only on the undercooling but also on its microstructure characteristics. In this paper the effect of isotacticity distribution on the isothermal kinetics of iPPs in the crystallization regime III was examined by differential scanning calorimetry. The microstructure features of two commercial film grade iPPs were characterized with temperature rising elution fractionation and size exclusion chromatography. The results indicated that, although the overall isotacticities and molecular weights of two iPPs were similar, their isothermal crystallization kinetics displayed marked differences due to the disparity in isotacticity distributions. With increasing molecular weight of components containing crystallizable units, the isothermal crystallization rate exhibited a higher temperature dependence. When the isotactic defects in polypropylene chains increase with the molecular weight of components, both the fold surface free energy σe and the work of chain folding q decreases, in spite of the higher molecular weight.© 2002 Society of Chemical Industry

Compatibility and Crystallization Studies on Poly(phenyl acetylene)/Polycaprolactone Blend

The compatibility and crystallization behavior of poly(phenyl acetylene) (PPA)/polycaprolactone (PCL) blends were investigated. PPA and PCL were partially miscible in the melt. PCL composition in the PCL-rich phase was calculated from the observed glass transition temperature with the consideration of the perturbation of amorphous phase composition by the crystallization of PCL. PCL composition in PCL-rich phase ranged from ca. 91 wt% to 94 wt%. The melting point of PCL was depressed upon blending. The isothermal crystallization kinetics of the blends was analyzed by Avrami equation. The crystallization rate decreased with increasing PPA composition in the PCL-rich phase. The crystal fold surface free energy σe of ca. 90 erg cm−2 was obtained from Lauritzen-Hoffman analysis considering regime II kinetics. Fold surface free energy was found to increase slightly with PPA composition.

Influence of crystallization and annealing conditions on the morphology of bulk‐crystallized isotactic polystyrene

AbstractThe influence of thermal history on the morphology of bulk‐crystallized isotactic polystyrene was investigated. Results from x‐ray diffraction (both wide‐ and small‐angle), DSC experiments, and electron microscope observations, were combined to define the influence of thermal history on the fold surface free energy σe. lamellar thickness, and crystallite perfection. The increase of the melting point with crystallization temperature is not only the consequence of an increase in lamellar thickness, but also of marked decrease of σe. Annealing above the crystallization temperature results in a fast reorganization to a more stable structure, as reflected in an increase in melting point. This reorganization, depending on the crystallization temperature, involves an increase in lamellar thickness, a decrease of σe, and eventually an increase in crystallite perfection.