Crystallization Half-time Research Articles

Effect of Organic Modifier and Clay Content on Non-Isothermal Cold Crystallization and Melting Behavior of Polylactide/Organovermiculite Nanocomposites.

In clay/polymer nanocomposites, the crystallization behavior and kinetics of the polymer can be affected by the presence of clay, its content and the degree of miscibility between the clay and the polymer matrix. The effect of two different organomodified vermiculites on the non-isothermal cold crystallization and melting behavior of polylactide (PLA) was studied by differential scanning calorimetry (DSC). In the presence of vermiculites, the cold crystallization of PLA occurred earlier, particularly for the highest content of the most miscible organovermiculite with PLA. The cold crystallinity of PLA decreased at low heating rates, notably at high organoclay loadings, and increased at high heating rates, especially at low vermiculite contents. According to the crystallization half-time, crystallization rate coefficient (CRC), and crystallization rate parameter (CRP) approaches, the cold crystallization rate of PLA increased by incorporating vermiculites, with the effect being most noteworthy for the vermiculite showing better compatibility. The Mo model was successful in describing the non-isothermal cold crystallization kinetics of the PLA/vermiculite composites. The melting behavior was affected by the heating rate and the type and content of clay. The nucleating effect of the most compatible clay resulted in the less perfect crystallites. The activation energy was evaluated using the Kissinger and Takhor methods.

Isothermal Kinetics of Poly(butylene adipate-co-butylene itaconate) Copolyesters with Ethylenediaminetetraacetic Acid.

A series of aliphatic copolyesters, poly(butylene adipate-co-butylene itaconate) (PBABI), have been synthesized using melt polycondensation of adipic acid (AA), itaconic acid (IA), 1,4-butanediol (1,4-BDO), and the tetra-functional group of ethylenediaminetetraacetic acid (EDTA, 0.1 mol %) to form partially cross-linking density as novel thermoplastic unsaturated copolyesters in our previous research. The crystal phase of PBABI copolyesters tended to prefer thermodynamics in the presence of a small amount of EDTA. The isothermal crystallization analysis revealed that the PBABI with EDTA exhibited a higher crystallization rate and a shorter half-time of crystallization than neat PBABI copolyesters. All of the sizes of spherulite/sheet crystals in the BA/BI = 9/1 are smaller than at BA/BI = 10/0 with or without a cross-linking agent, which demonstrated that the morphology behavior tended to form a small sheet crystal in the presence of 10 mol % IA, which played a dominant role in determining the average size of the crystal. These results deepen our understanding of the relationship among the cross-linking agent, the crystal form, and solidification time in PBABI copolyesters, making these kinds of polymers applicable to reinforce three-dimensional (3D) air-permeable polyester-based smart textiles.

Isothermal Crystallization Kinetics of Poly(ethylene terephthalate) Copolymerized with Various Amounts of Isosorbide

Poly(ethylene-co-isosorbide terephthalate) (PEIT) copolyesters could be used in various applications depending on their ability to crystallize. Moreover, the possibility to carry out solid-state post-condensation (SSP) is conditioned by its ability to sufficiently crystallize. The present study, thus, gives a systematic investigation of isothermal crystallization of these statistical copolyesters with isosorbide contents ranging from 4.8 to 20.8 mol.%. For each copolyester composition, the lowest isothermal half crystallization times and the highest Avrami constant (K) were obtained around 170 °C. Over the range of composition that was studied, both melting points and melting enthalpies decreased with increasing amounts of isosorbide (from 250 to 207 °C and from 55 to 28 J/g, respectively). On the contrary, half crystallization time displayed an exponential increase when increasing isosorbide contents in the studied range. Finally, structural and thermal analysis of PIT homopolyester are reported for the first time, showing that only ET moieties crystallized when PEIT was subjected to isothermal crystallization at 170 °C.

Phytic Acid Modified Boron Nitride Nanosheets as Sustainable Multifunctional Nanofillers for Enhanced Properties of Poly(l-lactide)

A sustainable multifunctional nanofiller (f-BNNSs) based on boron nitride nanosheets and biobased phytic acid was prepared using (γ-aminopropyl) triethoxysilane as a coupling agent. The structure of f-BNNSs was analyzed systematically using Fourier transform infrared spectroscopy, X-ray photoelectron spectroscopy, and elemental mapping. The influence of f-BNNSs on the crystallinity, polymorphism, crystallization kinetics, thermal stability, thermal conductivity, and flame retardant properties of poly(l-lactic acid) (PLLA) was systematically investigated. f-BNNSs show remarkable nucleating effects on the crystallization of PLLA, and the crystallization rate increases with increasing f-BNNSs loading. Upon addition of 20 wt % of f-BNNSs, the crystallization half-time of PLLA/f-BNNSs nanocomposite decreases from 12.0 to 1.0 min at 130 °C compared to PLLA. The presence of f-BNNSs in PLLA/f-BNNSs nanocomposites favors the formation of ordered α form irrespective of the loadings of f-BNNSs. Thermal stability and...

Enzymatic Degradation of Acrylic Acid-Grafted Poly(butylene succinate-co-terephthalate) Nanocomposites Fabricated Using Heat Pressing and Freeze-Drying Techniques.

Biodegradable acrylic acid-grafted poly(butylene succinate-co-terephthalate) (g-PBST)/organically modified layered zinc phenylphosphonate (m-PPZn) nanocomposites were effectively fabricated containing covalent bonds between the g-PBST and m-PPZn. The results of wide-angle X-ray diffraction and transmission electron microscopy revealed that the morphology of the g-PBST/m-PPZn nanocomposites contained a mixture of partially exfoliated or intercalated conformations. The isothermal crystallization behavior of the nanocomposites showed that the half-time for crystallization of 5 wt % g-PBST/m-PPZn nanocomposites was less than 1 wt % g-PBST/m-PPZn nanocomposites. This finding reveals that increasing the loading of m-PPZn can increase the crystallization rate of nanocomposites. Degradation tests of g-PBST/m-PPZn nanocomposites fabricated using the heat pressing and the freeze-drying process were performed by lipase from Pseudomonas sp. The degradation rates of g-PBST-50/m-PPZn nanocomposites were significantly lower than those of g-PBST-70/m-PPZn nanocomposites. The g-PBST-50 degraded more slowly due to the higher quantity of aromatic group and increased stiffness of the polymer backbone. The degradation rate of the freeze-drying specimens contained a more extremely porous conformation compared to those fabricated using the heat pressing process.

Isothermal cold crystallization kinetics and properties of thermoformed poly(lactic acid) composites: effects of talc, calcium carbonate, cassava starch and silane coupling agents

The effects of three different fillers (i.e., talc, calcium carbonate, and cassava starch) and surface functionalization by 3-aminopropyltriethoxysilane (APTES) and vinyltriethoxysilane (VTES) on morphology, thermal and tensile properties of the poly(lactic acid) (PLA) composites were comparatively examined. Dynamic differential scanning calorimetry (DSC) results revealed that the incorporation of filler can facilitate the cold crystallization of PLA, as confirmed by lowered cold crystallization temperature. By fitting DSC data with Avrami model, the highest isothermal cold crystallization rate constant k and the shortest crystallization half time t1/2 were obtained for the PLA/talc composites under isothermal temperature of 100 °C, implying that talc was the most effective nucleating agent for PLA in this study. The average Avrami index n of neat PLA and its composites lay within the same range of 3.0–3.6, which reflected the three-dimensional spherulitic growth of PLA with the mixture of instantaneous nuclei and sporadic nuclei. In comparison with the composite cast films, the thermoformed films had higher degree of crystallinity as well as higher tensile strength and Young’s modulus owing to the chain orientation upon annealing. Furthermore, the addition of silane-treated talc, especially APTES-treated talc, fastened cold crystallization rate and enhanced tensile properties because of the improved interfacial interaction between talc particles and PLA matrix.

Effects of hydrogen-bonding density on polyamide crystallization kinetics

We employed Flash DSC1 apparatus for fast-scan chip-calorimeter measurement in a broad temperature range to compare the isothermal crystallization rates among six polyamide/nylon (PA) samples, i.e. PA 46, PA 66, PA 610, PA 612, PA 1012 and PA 12. The double parabolic curves of crystallization half-time versus crystallization temperature revealed that PA 46 crystallizes relatively fast due to its high hydrogen-bonding density favoring thermodynamic driving forces for crystallization in the high temperature region, while PA 1012 and PA 12 crystallize relatively fast due to their low hydrogen-bonding densities favoring short-range diffusion for crystallization in the low temperature region. Furthermore, the cross-over temperatures between two parabolic curvatures of six samples follow their sequences in hydrogen-bonding density, and the Avrami indexes reveal a potential switching in the modes between heterogeneous and homogeneous crystal nucleation.

Crystallization kinetics and morphology of small concentrations of cellulose nanofibrils (CNFs) and cellulose nanocrystals (CNCs) melt-compounded into poly(lactic acid) (PLA) with plasticizer

In the present study, very small concentrations of CNCs and CNFs were melt-compounded into PLA using a solvent-free process where poly(ethylene glycol) (PEG) was used to disperse the nanoparticles in PLA. As a comparison, the commercial nucleant, talc, was processed similarly into PLA. CNC and CNF were shown to be efficient nucleants for PLA, similar to talc, and conventional Avrami and Lauritzen-Hoffman analysis of the crystallization behavior was performed for isothermal temperatures from 90 °C to 130 °C across all compositions. From the Avrami analysis, the crystallization rate, half-time, and Avrami exponent were calculated and suggested a synergistic effect of nanocellulose and PEG, even at very small concentrations. The crystallization half-time was lower than talc at higher temperatures indicating faster crystallization for samples containing nanocellulose under certain conditions. Analysis of secondary nucleation revealed a decrease in the surface energy for CNC containing samples, further suggesting that, given the enhanced mobility of plasticized PLA, very small concentrations of CNC are effective nucleation agents. Lastly, scanning electron microscopy was used to correlate the crystal morphology of chemically etched samples with the thermal analysis. Coarsening of the microstructure was observed initially with the addition of PEG, and further coarsening was observed upon the addition of nanocellulose.

Stereocomplex crystallization, homocrystallization, and polymorphism of enantiomeric copolyesteramides poly(lactic acid‐ co ‐alanine)s from the melt

Stereocomplex (SC) crystallization, homocrystallization, and polymorphism of poly(l-lactic acid-co-l-alanine) [P(LLA-LAL)] and poly(d-lactic acid-co-d-alanine) [P(DLA-DAL)] copolymers with wide alanine unit content ranges from 0 to 21 and 22 mol% are investigated for melt-crystallization. P(LLA-LAL)/P(DLA-DAL) blends crystallize for wide alanine unit content ranges compared to unblended P(LLA-LAL) and P(DLA-DAL) samples, due to facile SC crystallization compared to homocrystallization. The phase diagrams of the unblended samples [α- and δ-form homocrystallites] and the blend samples (SC and homocrystallites) are drawn. The transition crystallization temperature of unblended samples from α-form to δ-form decreases with an increase in alanine unit content. In the unblended and blend samples, alanine units are correspondingly incorporated in α-form homocrystalline regions and excluded from SC crystalline regions. The maximum radial growth rate values of spherulites are higher for the blend samples than for the unblended samples. The experimental crystallization half time [tc(1/2)(exp)] values of the unblended samples increase with an increase in alanine unit content, whereas the tc(1/2)(exp) values of the blend samples with alanine unit contents of 3 and 4 mol% and 6 and 6 mol% and of 12 and 13 mol% are respectively higher than and similar to those of poly(l-lactic acid)/poly(d-lactic acid) blend.

Achieving highly crystalline rate and crystallinity in Poly(l-lactide) via in-situ melting reaction with diisocyanate and benzohydrazine to form nucleating agents

The drawback of the application for poly(l-lactide) (PLLA) is the low crystalline rate and crystallinity obtaining via normal processing methods. Modifying crystallization of PLLA has been found to be an efficient way to improve its mechanical and heat resistance properties. In this wok, 4, 4′-diphenylmethane diisocyanate (M) and benzohydrazine (P) were employed into PLLA melt to in-situ form nucleating agents. The in-situ melting reaction was confirmed by a nuclear magnetic resonance spectroscopy. The crystallization behavior and crystalline morphology were investigated by a differential scanning calorimetry, a polarized optical microscopy and a field emission scanning electron microscope. The crystalline rate of PLLA was abruptly enhanced by adding (M+P) and melting reaction with PLLA. The crystallization half-time of PLLA dramatically decreased from 42.0 to 1.1 min at 130 °C by the in-situ formation of nucleating agents. The crystallinity of PLLA increased from 10.3 to 42.1 by adding 0.25% (M+P) and melting reaction for 8 min. Furthermore, the size of PLLA crystals was dramatically reduced because of the nucleating effect. Accompanied with improvement on crystallinity, the Vicat softening temperature of PLLA shifted from 57.4 °C to 93.7 °C by the in-situ reaction with 6.00% (M+P), and indicating heat resistance enhancement.

Nucleus density and crystallization behavior of isotactic polypropylene nucleated with different α/β compound nucleating agents

Different compound nucleating agents consisting of a highly efficient novel α-nucleating agent N,N’-bis(benzoyl) sebacic acid dihydrazide and three typical β-nucleating agents N,N-dicyclohexylterephthalamide, rare earth compound (WBG-II) and calcium pimelate were incorporated into isotactic polypropylene (iPP), and the isothermal crystallization behavior of iPP nucleated with these compound nucleating agents was investigated by differential scanning calorimetry. Based on the classical Avrami theory and the calorimetric curves under isothermal conditions, the crystallization half-time and the Avrami index can be calculated. The results demonstrate that addition of these nucleating agents reduced the crystallization half-time and speed up the crystallization process of iPP. In addition, the nucleus density of pure and nucleated iPP was further calculated from the Lamberti model and the results illustrate that the nucleus density of iPP after addition of different compound nucleating agents was increased greatly and it was several orders of magnitude higher than that of pure iPP.

A novel approach of preparing zinc adipate as β-nucleating agent for polypropylene engineering

Abstract

Crystallization and Rheological Properties of the Eco-friendly Composites Based on Poly (lactic acid) and Precipitated Barium Sulfate

The environmental-friendly poly (lactic acid) (PLA) composites were fabricated by incorporating precipitated barium sulfate (BaSO4), and then the crystallization behaviors and rheological properties were investigated in detail. Results show that the added inorganic filler enhances the crystallization capacity, promoting the crystallization happened in advance and achieving increased crystallinity for the composites. Such promotion effect is further demonstrated by the calculated kinetic parameters including half-time of crystallization, F(T), activation energy and nucleation activity. Rheology tests reveal that pure PLA exhibits a typical linear viscoelastic feature while the shear-thinning behavior of the composites becomes manifest increasingly. However, the complex viscosity, storage modulus and loss modulus for the composites are all increased along with added inorganic filler.

Influence of Two Different Nanofillers on the Crystallization Behavior and Dynamic Mechanical Properties of Biodegradable Poly(ethylene adipate)

In this work two biodegradable poly(ethylene adipate) (PEA) based nanocomposites containing the same low loading of cellulose nanocrystals (CNC) and carboxyl-functionalized multi-walled carbon nanotubes (f-MWCNT) were prepared through a solution and casting method, respectively. The crystallization behavior and dynamic mechanical properties of neat PEA and the nanocomposites were studied in detail and compared with each other. Both CNC and f-MWCNT finely dispersed in PEA matrix. The addition of CNC or f-MWCNT not only increased the melt crystallization peak temperature but also decreased the crystallization half-time of PEA, suggesting that the crystallization of PEA was apparently enhanced by CNC or f-MWCNT due to the heterogeneous nucleating agent effect. Both CNC and f-MWCNT increased the storage modulus and glass transition temperature of PEA matrix in the nanocomposites. As a nucleating agent, f-MWCNT was more efficient than CNC, while CNC was stronger than f-MWCNT as a reinforcer.

Isothermal and non-isothermal crystallization kinetics of PLA/PBS blends with talc as nucleating agent

The isothermal and non-isothermal crystallization kinetics of PLA/PBS at the blend ratio of 90/10 by mass containing 0.1% of talc was studied by differential scanning calorimetry. In this study, Avrami and Tobin equations were used to explain isothermal crystallization kinetics. The results of both theoretical models offered the same trend results which were the different crystallization temperatures influenced crystallization rate and the amount of crystallinity. It was found that at 100 °C is the temperature for the fastest of the completion of the crystallization blending process. Both models were also used to calculate the overall kinetic rate constant, n value, half-time of crystallization and growth rate. They indicated that growth dimension was three-dimensional which is the spherulitic growth from instantaneous nuclei of heterogeneous nucleation and occurred from talc. For non-isothermal crystallization kinetics, Jeziorny and Ozawa equations were used to explain. The results from Jeziorny equation show that there are two stages of crystallization at high cooling rate, the straight line in the primary stage followed by the nonlinear line in the secondary stage. It was also found that Jeziorny crystallization rate increased when the cooling rate increased. However, the Ozawa model was inappropriate for describing the non-isothermal crystallization for these blends.

Numerical study of the relationship between the spherulitic microstructure and isothermal crystallization kinetics. Part I. 2-D analyses

In this paper, we proposed a numerical model to study the kinetic properties and the spherulite microstructure of a semi-crystalline polymer under isothermal crystallization, which further exhibits the potential in generating the 2D spherulitic structure according to the observations obtained by experimental techniques. Two characteristic parameters are introduced, namely, characteristic length Lc and characteristic time tc, which are dependent on the growth rate, G and the nucleation rate, I. In addition, two non-dimensional parameters are introduced to model the nucleation saturation: Ld/Lc and t⋆/tc, which is related to the thickness of nucleation exclusion zone Ld, and the effective nucleation time t⋆, respectively. In 2D modeling, the kinetics are confirmed by Avrami fitting, and the effects of the four characteristic parameters on the Avrami parameter n and the crystallization half-time t0.5 are presented. The regularity of how the spherulite density or the mean radius of spherulites R‾ change along with these parameters are also given, respectively. It shows that Lc is the prominent parameter for the size of the spherulite, and tc controls t0.5 as long as there is no nucleation saturation (Ld=0 and t⋆→∞). Besides, the existence of the nucleation saturation increases the mean radius of spherulites, but decreases n from 3 to 2 in 2-D modeling. Finally, a relationship between crystallization kinetics and microstructures is provided, giving a new perspective to estimate the nucleation rate.

Accelerated crystallization of poly(l-lactic acid) by silk fibroin nanodisc

Slow crystallization of poly(l-lactic acid) (PLLA) limits the widespread applications of PLLA because of its insufficient thermal and mechanical properties. In this study, a biobased filler, silk fibroin nanodisc (SFN), has been included in the PLLA matrix with the aim of accelerating the crystallization process of PLLA. Detailed investigation of the effect of SFN inclusion on the crystallizability of PLLA has been performed by polarizing optical microscope (POM) observations and differential scanning calorimetry (DSC) measurements. For isothermal crystallization studies by DSC, extremely quick cooling (~300 °C/min) from the melt to the crystallization temperature was conducted in order to avoid nucleation during the cooling process. The experimental results show that the small amount of SFN (only 1%) can significantly enhance the crystallizability of PLLA. The glass transition temperature and the melting temperature of PLLA were not influenced by the inclusion of SFN. However, the nucleation rate and the final degree of crystallinity were significantly enhanced. The effect of optical purity on the acceleration ability of SFN was examined in this research by utilizing two different types of PLLA having different contents of the D moiety (0.5 and 1.4%). As a result, it was found that the extent of enhancement is much larger in the case of highly optical pure PLLA (0.5% D moiety). The nucleating effect of silk fibroin nanodisc on the crystallization behavior of poly(l-lactic acid) (PLLA) was investigated by polarizing optical microscope observations and the differential scanning calorimetry measurements. The experimental results show that the small amount of SFN (only 1%) reduces the induction period and the crystallization half-time while it increases the final degree of crystallinity. It was found that the SFN works as a nucleation agent by increasing the number of nuclei about four times while it does not change the growth rate of spherulites.

Heterogeneous Nucleation Effect of N, N'-Adipic Bis(4-phenylbutyric Acid) Dihydrazide on Crystallization Process of Poly(L-lactic Acid)

Enhancing crystallization ability is a fundamental challenges in Poly(L-lactic acid) (PLLA) industry, therefore, the goal of this work was to synthesis a new organic nucleating agent N, N'-adipic bis(4-phenylbutyric acid) dihydrazide (APAD), and investigate its effect on non-isothermal crystallization, isothermal crystallization, melting behavior, thermal stability, and optical property of PLLA. Non-isothermal melt crystallization results showed that APAD acted as more effective nucleating and accelerating agent for the crystallization of PLLA, as a result, upon cooling at 1 °C/min, PLLA/0.5 %APAD had the highest onset crystallization temperature 136.4 °C and the crystallization peak temperature 132.0 °C, as well as the largest non-isothermal crystallization enthalpy 48.1 J/g. However, with increasing of APAD concentration from 0.5 wt.% to 3 wt.%, the crystallization peak shifted to the lower temperature. In contrast, for the non-isothermal cold crystallization process, the effect of APAD concentration on the crystallization behavior of PLLA was negligible. Additionally, the non-isothermal crystallization process was also depended on the cooling rates and the final melting temperature. In isothermal crystallization section, to compare with the primary PLLA, the crystallization half-time of PLLA/APAD could decrease from 254.3 s to the minimum value 29.4 s, with 0.5 wt.% APAD contents at 125 °C. Melting behavior of PLLA/APAD samples under different conditions further confirmed the heterogeneous nucleation effect of APAD for PLLA, and the appearance of the double melting peaks was attributed to the melting-recrystallization. Finally, the addition of APAD decreased the thermal stability to some extent, although APAD could not change the thermal decomposition profile of PLLA. And a drop of PLLA/APAD samples in light transmittance resulted from the double influence of the enhancement of crystallization and the opaqueness of APAD.

Structural Evolution in Isothermal Crystallization Process of Poly(L-lactic acid) Enhanced by Silk Fibroin Nano-Disc.

The nucleating effect of silk fibroin nano-disc (SFN) on the crystallization behavior of poly(L-lactic acid) (PLLA) was investigated by simultaneous synchrotron small- and wide-angle X-ray scattering measurements. For the isothermal crystallization at 110 °C from the melt, the induction period of the PLLA specimens containing 1% SFN was reduced compared to that of the neat specimens, indicating the acceleration of the nucleation of PLLA. The final degree of crystallinity was also increased, and the crystallization half-time was decreased, which indicates that the overall crystallization process was accelerated. Furthermore, the final value of the crystallite size (the lateral size of the crystalline lamella) was slightly lower for the specimens containing 1% SFN than that for the PLLA neat specimen, although the crystallites started growing much earlier. However, it was found that there was no effect of SFN on the growth rate of the crystallite size. The lamellar thickening process was also accelerated with a clear overshooting phenomenon with the inclusion of 1% SFN. As for the polymorphism, the α’ phase is dominant with about 96%, but a small amount of the α phase (4%) is found to exist. It was found that the SFN can also accelerate the formation of the minor α phase as well as the major α’ phase.

Effect of different nucleating agent on crystallization kinetics and morphology of polypropylene

AbstractThe effects of phosphate nucleating agent (NA), carboxylate nucleating agent (MD), rosin type nucleating agent (WA) and sorbitol nucleating agent (NX) on crystallization behavior of isotactic polypropylene were investigated by fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), differential scanning calorimetry (DSC) and polarized light microscopy (PLM). The results showed that different structure nucleating agents significantly affected the crystallization kinetics, rate and temperature of polypropylene. Among them, half crystallization time of NX nucleating agent was the shortest, which was 53.4 seconds, and the crystallization temperature was the highest, reaching 129.8°C.