Cold Crystallization Behavior Research Articles

Heat Treatment and Chemical Composition of Fatty Acids and Rosin Acids Mixtures: Effects on Their Thermal Properties and Morphology

AbstractMixtures of fatty acids and rosin acids are industrially important products utilized as a raw material for several purposes. Their thermal properties, especially cold stability and crystallization behavior is also important. Several fatty acid and rosin acid mixtures both from industrial products and from commercially available fatty and rosin acids were prepared and treated for 30 min at 80 °C under an inert atmosphere. Thereafter, the mixture was cooled to the desired temperature. Determination of the cloud point, chemical analysis of liquid and solid phase, thermal analysis by differential scanning calorimetry as well as morphology analysis by scanning electron microscopy were performed. The results revealed that crystallization was more rapid when it occurred at 10 °C compared to 25 °C. The crystal sizes increased with decreasing the crystallization temperature. Furthermore, crystals were of irregular shape and agglomerated when rapid cooling of the mixture occurred. Chemical analysis revealed that liquid phase was enriched with stearic acid, whereas crystals contained large amounts of abietic, dehydroabietic and linoleic acids. The cloud point of the mixtures increased with increasing amount of stearic and rosin acids. Dehydroabietic acid addition improved the cold stability of the synthetic fatty acid–rosin acids mixture.

In situ ring-opening polymerization of poly(l-lactide)-graft-graphene oxide and its effect on the crystallization kinetics and morphology of biodegradable poly(l-lactide) at low loadings

Biodegradable poly(L-lactide) (PLLA) and graphene oxide (GO) nanocomposites were prepared by blending commercial PLLA with PLLA-g-GO at low loadings, which was synthesized via ring-opening polymerization using GO as the initiator and characterized with various techniques. Both the nonisothermal cold and melt crystallization behaviors and overall isothermal melt crystallization rates of PLLA have been enhanced significantly by PLLA-g-GO in the nanocomposites, relative to neat PLLA. PLLA-g-GO is more efficient than GO as a nucleating agent for the crystallization of PLLA, because PLLA is covalently grafted onto the surface of GO in PLLA-g-GO, which may provide better compatibility with the PLLA matrix and improve the nucleation ability.

Non-isothermal cold crystallization behavior and kinetics of poly(l-lactide): effect of l-lactide dimer

The effects of l-lactide dimer as additives on the crystallization behavior of poly(l-lactide) (PLLA) films were studied. Hence, neat PLLA films and PLLA containing l-lactide (5 % w/w) (PLLA/La) were prepared in dichloromethane at room temperature via solution casting. The non-isothermal cold crystallization of PLLA films were studied using differential scanning calorimetry at various heating rates including 2.5, 5, 7.5, 10 and 15 °C/min. However, the X C% was increased for PLLA/La films in comparison with neat PLLA films. The crystallization kinetics was then analyzed by the Avrami, Jeziorny, Ozawa and Mo kinetic models. It is found that all the kinetic models were established to describe the experimental data fairly well except the Ozawa model. The values of t 1/2, Z C and F(T) indicated that the crystallization rate increased with increase in heating rates for PLLA and PLLA/La films. However, l-lactide dimer incorporated in PLLA films accelerates the crystallization process of PLLA at the high heating rate. The nucleation constant (K g) and the surface free energy (σ e) based on Lauritzen–Hoffman theory indicated that these parameters for PLLA/La films is lower than neat PLLA.

Crystallization Behavior of Polylactide/Graphene Composites

Polylactide (PLA) composites containing graphene nanosheets were prepared by the approach of solution mixing for a crystallization study. The results revealed that the graphene nanosheets are well distributed in the PLA matrix, leading to an evident viscosity increase despite their dispersion as multilayered structures in stack form. Both the cold and melt crystallization behaviors of PLA were found to depend strongly on the presence of the graphene nanosheets. During cold crystallization, the graphene nanosheets merely act as an inert filler, and the increased viscosity results in a decrease of the overall crystallization rate of the composite relative to neat PLA. However, the graphene nanosheets can act as a heterogeneous nucleating agent, which is their dominant role during melt crystallization. As a result, the composite shows a higher crystallization rate than neat PLA under these conditions.

Effect of Low Octavinyl-Polyhedral Oligomeric Silsesquioxanes Loading on the Crystallization Kinetics and Morphology of Biodegradable Poly(ethylene succinate-co-5.1 mol % ethylene adipate) as an Efficient Nucleating Agent

In this work, a biodegradable polymer composite was prepared by mixing poly(ethylene succinate-co-5.1 mol % ethylene adipate) (PESA) and octavinyl-polyhedral oligomeric silsesquioxanes (ovi-POSS) at a very low ovi-POSS loading. It is found that a fine dispersion of ovi-POSS has been achieved in the PESA matrix. The effects of ovi-POSS on the nonisothermal melt and cold crystallization behaviors, overall isothermal melt crystallization kinetics, spherulitic morphology, and crystal structure of PESA in the composite were studied in detail with various techniques. Relative to neat PESA, both the nonisothermal melt and cold crystallization behaviors and isothermal melt crystallization kinetics of PESA have been enhanced significantly in the composite. Ovi-POSS is an efficient nucleating agent for the crystallization of PESA, because the nucleation density of PESA spherulites is apparently higher in the composite than in neat PESA; however, the crystallization mechanism and crystal structure of PESA remain unchanged in the composite.

Isothermal and Nonisothermal Cold Crystallization Behaviors of Asymmetric Poly(l-lactide)/Poly(d-lactide) Blends

Isothermal and nonisothermal cold crystallization behaviors of asymmetric poly(l-lactide) (PLLA)/poly(d-lactide) (PDLA) blends at PDLA loadings of 0–20 wt % were investigated in this work. Formation of the stereocomplex in the blends was confirmed by differential scanning calorimetry and wide-angle X-ray diffraction. For both neat PLLA and its blends, the overall isothermal cold crystallization rates increase with increasing crystallization temperature; moreover, the overall isothermal cold crystallization rates of PLLA are faster in the blends than in neat PLLA, indicative of the nucleating agent effect of the stereocomplex formed in the blends. Crystallization mechanism and crystal structure of PLLA remain unchanged despite the PDLA loading. For the nonisothermal cold crystallization, the crystallization process of PLLA is accelerated by increasing both heating rate and the PDLA loading up to 10 wt %. The Ozawa equation failed to fit the crystallization process, while the Tobin equation could describe it well in the relative degree of crystallization range of 0–75%.

Isothermal Crystallization Kinetics, Morphology, and Mechanical Properties of Biocomposites Based on Poly(3-hydroxybutyrate-co-4-hydroxybutyrate) and Recycled Carbon Fiber

The biocomposites of poly(3-hydroxybutyrate-co-4-hydroxybutyrate) [P(3,4HB)] and recycled carbon fiber (RCF) were prepared via a melting extrusion. The crystallization behaviors and kinetics of the P(3,4HB) matrix in composites were exclusively studied under both nonisothermal and isothermal conditions. The corresponding results indicated that the P(3,4HB) either neat or compositing with RCF had a dual-peak cold crystallization behavior in the nonisothermal condition, and the isothermal crystallization rate of P(3,4HB) in composites was jointly determined by the rates of the nucleation and the crystal growth and integrity. However, it was reduced with the incorporation of RCF. Wide-angle X-ray scattering investigation demonstrated that the presence of RCF did not change the crystallization mechanism and crystalline structure of the P(3,4HB) matrix, but the crystallinity of the P(3,4HB) either neat or compositing with RCF was enhanced with an increase of crystallization temperature. Dynamic mechanical anal...

Comparative study of poly(L‐lactide) nanocomposites with organic montmorillonite and carbon nanotubes

AbstractOrganic montmorillonite (OMMT) and the one‐dimensional functionalized multiwalled carbon nanotubes (FMWCNTs) were introduced into poly(L‐lactide) (PLLA) to prepare PLLA/OMMT and PLLA/FMWCNT nanocomposites, respectively. The effects of nanofillers on melt crystallization and cold crystallization of PLLA were comparatively investigated by using polarized optical microcopy, differential scanning calorimetry and wide angle X‐ray diffraction. The results show that FMWCNTs exhibit higher nucleation efficiency for the melt crystallization of PLLA, whereas OMMT is the better one for the cold crystallization of PLLA. Rheological properties show that both OMMT and FMWCNTs at relatively higher concentrations can form the percolated network structure in the PLLA matrix, however, the latter nanocomposites exhibit relatively denser or more compact percolated networks. The difference of the networks between OMMT and FMWCNTs is suggested to be the main reason for the different cold crystallization behaviors observed in the PLLA/OMMT and PLLA/FMWCNT nanocomposites. The dynamic mechanical analysis measurements show that OMMT is the better one to improve the stiffness of the nanocomposites in the present work. The thermogravimetric analysis measurements show that FMWCNTs have higher efficiency in improving the thermal stability of PLLA compared with OMMT. © 2012 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys, 2013

Improving the Barrier Properties of Poly(Lactic Acid) by Blending with Poly(Ethylene-Co-Vinyl Alcohol)

Poly(lactic acid) (PLA)/poly(ethylene-co-vinyl alcohol) (EVOH) blends were prepared via melt blending to improve the barrier properties of PLA. The phase morphologies and final properties (rheological behavior, thermal and dynamical-mechanical features, barrier properties, and mechanical behaviors) of the blends were investigated as a function of the EVOH content. The results indicated that hydroxyl groups of EVOH promoted the degradation of PLA, and thus affected the viscosities and morphologies of the resulting blends. The intrinsic viscosities of PLA in the blends decreased with the content of EVOH. The PLA and EVOH presented typical phase-separated morphologies, with a relatively small domain size of the EVOH phase. The EVOH enhanced the cold-crystallization behavior of PLA. The barrier properties to water vapor and oxygen increased linearly with increasing EVOH content.

Cold‐crystallization behavior of poly(L‐lactide)/ACR blend films investigated by in situ FTIR spectroscopy

AbstractThe cold crystallization behavior of poly (L‐lactide) (PLLA) blend films modified by small amount of acrylic rubber particles (ACR) have been investigated by in situ Fourier‐transform infrared (FTIR) spectroscopy. During the isothermal cold crystallization, the crystallization rate of PLLA is greatly improved with addition of only 1 wt % ACR. However, for PLLA with 8 wt % ACR, the crystallization rate is slower than that of neat PLLA. The relative crystallinity of PLLA with the addition of 1–5 wt % ACR is obviously higher than that of the neat PLLA. For the PLLA blend film with 3 % ACR, the relative crystallinity reaches a maximum. It was found that the addition of ACR particles below 5% accelerated the cold crystallization nucleation process and made the cold‐crystallization rate of PLLA/ACR be quicker than that of neat PLLA. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013

Highly improved crystallization behavior of poly(L‐lactide) induced by a novel nucleating agent: substituted‐aryl phosphate salts

In this work, a novel nucleating agent (NA) based on substituted‐aryl phosphate salts was introduced into poly(L‐Lactide) (PLLA). The nonisothermal and isothermal crystallization behaviors of nucleated PLLA samples were investigated through differential scanning calorimetry (DSC), wide angle X‐ray diffraction, and polarized optical microscope (POM). Furthermore, the effect of annealing treatment on the cold crystallization behaviors of nucleated samples was also investigated. The results show that the crystallization of PLLA, whether for the melt crystallization (including nonisothermal and isothermal crystallization process) or for the cold crystallization (including the cold crystallization occurring during the DSC heating process and during the annealing process), is greatly dependent upon the content of NA. At relatively lower NA content (≤0.1 wt%), the nucleation effect of NA is inconspicuous, however, at higher NA content (≥0.2 wt%), it exhibits great nucleation effect for the crystallization of PLLA. Further results show that the double endothermic peak of PLLA depends on the temperature applied for the crystallization. Copyright © 2012 John Wiley & Sons, Ltd.

Elastic Light Scattering Studies on Cold-crystallization Behaviors of Syndiotactic Polystyrene

The cold-crystallization behavior of syndiotactic polystyrene (sPS) and its isothermal kinetics were studied by elastic scattering method in this work. It was shown that the scattering signal was very sen- sitive to the conformational change of sPS chains upon heating. The glass transition temperature (Tg) and cold-crystallization temperature (Tc) obtained by elastic scattering were in good agreement with those meas- ured by DSC method. In addition, it can be clearly observed in the plot of temperature-dependent scattering intensity, there are several stages during the cold-crystallization process, i.e., nucleation phase, nucleus growth phase and secondary crystallization phase. By using isothermal scattering data and Arrhenius equation, the apparent activation energy of cold-crystallization of sPS was estimated to be 309 kJ/mol.

Isothermal and Nonisothermal Cold Crystallization Behaviors of Biodegradable Poly(l-lactide)/Octavinyl-Polyhedral Oligomeric Silsesquioxanes Nanocomposites

Isothermal and nonisothermal cold crystallization behaviors of biodegradable poly(l-lactide) (PLLA)/octavinyl-polyhedral oligomeric silsesquioxanes (ovi-POSS) nanocomposites at low ovi-POSS loadings were investigated in this work. For both neat PLLA and its nanocomposites, the overall isothermal cold crystallization rates increase with increasing crystallization temperature; moreover, the overall isothermal cold crystallization rates of PLLA increase with increasing the ovi-POSS loading in the nanocomposites relative to neat PLLA, indicative of the nucleating agent effect of ovi-POSS. Crystallization mechanism and crystal structure of PLLA remain unchanged despite the ovi-POSS loading. For the nonisothermal cold crystallization, the crystallization process of PLLA is accelerated by increasing both heating rate and the ovi-POSS loading. The Ozawa equation failed to fit the crystallization process, while the Tobin equation could describe it well. The activation energies of nonisothermal cold crystallization were calculated by the Kissinger method, which increase with increasing the ovi-POSS loading in the nanocomposites relative to neat PLLA.

Unusual Cold Crystallization Behavior in Physically Aged Poly(l-lactide)

A comparative study of cold crystallization behavior in poly(L-lactide) (PLLA) annealed below and just above the glass transition temperature (T(g)) has been conducted. Annealing benefits the generation of local order and the subsequent cold crystallization process, which becomes significant in PLLA annealed just above T(g). Surprisingly, morphological observation reveals high density nuclei in PLLA annealed below T(g), contrary to its relatively slow crystallization kinetics. This unusual crystallization behavior in physically aged PLLA arises from the retarded crystal growth rate because of incomplete recovery of reduced segmental mobility above T(g). In contrast, annealing just above T(g) has little influence on the crystal growth rate, and the increased nucleation density alone accounts for the accelerated crystallization rate.

The plasticizer‐assisted formation of a percolating multiwalled carbon nanotube network in biodegradable poly(L‐lactide)

AbstractA plasticizer, polyethylene glycol (PEG), was used to disperse multiwalled carbon nanotubes (MWCNTs) in biodegradable poly(L‐lactide) during one‐step melt mixing. Incorporation of PEG significantly promotes the formation of a percolating MWCNT network in the plasticized composites, as revealed by rheological measurements and morphological observations. It, in turn, results in the retarded glass transition and cold crystallization behaviors in these plasticized composites as a result of constrained chain relaxation. It is believed that noncovalent wrapping of MWCNTs by PEG is responsible for the improved affinity between MWCNTs and the poly(L‐lactide) matrix. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012

Carbon nanotubes induced microstructure and mechanical properties changes in cocontinuous poly( L‐lactide)/ethylene‐co‐vinyl acetate blends

AbstractToughening of poly( L‐lactide) (PLLA) by elastomer attracts much attention in recent years; however, it is usually associated with the deterioration of modulus and/or strength, resulting in limitation in many applications of the material. In this work, functionalized multiwalled carbon nanotubes (FMWCNTs) were introduced into ethylene‐co‐vinyl acetate toughened PLLA blends. The effects of FMWCNTs content on crystalline structure of PLLA matrix and the morphology of the blends, as well as the selective distribution of FMWCNTs in the ternary nanocomposites were investigated using differential scanning calorimetry (DSC), wide angle X‐ray diffraction, scanning electron microscope, and transmission electron microscope. The results show that FMWCNTs exhibit excellent nucleation role in improving the cold crystallization behaviors of PLLA during the annealing and/or DSC heating processes. The results of mechanical property measurements demonstrate that the modulus, strength, and ductility of the blends can be further improved simultaneously through introducing FMWCNTs. Copyright © 2011 John Wiley & Sons, Ltd.

Thermal, crystalline, and mechanical properties of octa(3‐chloropropylsilsesquioxane)/ poly(L‐lactic acid) hybrid films

AbstractA series of organic‐inorganic hybrid films were prepared based on octa(3‐chloropropylsilsesquioxane) (OCPS) and poly(L‐lactic acid) (PLLA) via simply solution blending method. The thermal, crystalline and mechanical properties of OCPS/PLLA hybrid films were characterized by Fourier transform infrared, scanning electron microscopy, energy dispersive spectrometer, differential scanning calorimetry (DSC), X‐ray diffraction, polarized optical microscopy, thermogravimetric analysis (TGA), and tensile tests. The results showed that OCPS could be dispersed well at molecular level when its content was less than 3 wt % and began to crystallize in PLLA matrix when the content increased to 5 wt %. DSC study revealed that OCPS acted as a plasticizer to decrease both Tg and Tm of the PLLA matrix at various heating rates. The addition of OCPS did not change the crystal form of PLLA, while had an great influence on the cold crystallization and melting behaviors of PLLA in the second heating cycles. Moreover, the initial crystallinity of OCPS/PLLA was higher than that of pure PLLA. The results suggested that OCPS could be an effective heterogeneous nucleating reagent to promote the crystallization of PLLA. TGA showed that the PLLA thermal degradation mechanism remained unchanged, whereas the weight loss temperatures and residual weights were improved. Tensile tests indicated that the incorporation of OCPS into PLLA matrix changed the tensile behavior of the hybrid films from brittle to ductile, and the strain at break was improved remarkably as a result of the plasticizer effect of OCPS. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011

Nonisothermal and Isothermal Cold Crystallization Behaviors of Biodegradable Poly(p-dioxanone)

Nonisothermal and isothermal cold crystallization behaviors of poly(p-dioxanone) (PPDO) were investigated by differential scanning calorimetry (DSC). There were two crystallization exotherms—a majo...

Crystallization studies on a clay nanocomposite prepared from a degradable poly(ester amide) constituted by glycolic acid and 6‐aminohexanoic acid

AbstractAn intercalated nanocomposite was prepared from an organomodified clay (Cloisite 25A) and a new biodegradable poly(ester amide) characterized by an alternating arrangement of glycolic acid and 6‐aminohexanoic acid units by the melt‐mixing technique. The influence of the final silicate layer morphology on hot and cold crystallization behavior was investigated by optical microscopy, differential scanning calorimetry, and synchrotron radiation. Primary nucleation increased significantly with the incorporation of nanoparticles, in contrast with the decrease previously observed when exfoliated structures were obtained. The secondary nucleation constant was higher for the nanocomposite sample, indicating that the growth mechanism was hampered by the presence of clay particles. However, the increase in primary nucleation had a greater effect, resulting in a faster overall crystallization rate for the nanocomposite. The addition of clay particles slightly reduced the degree of crystallinity attained after the hot and cold crystallization processes and favored a lamellar insertion mechanism. POLYM. ENG. SCI., 2011. © 2011 Society of Plastics Engineers

Intermolecular interactions and crystallization behaviors of biodegradable polymer blends between poly (3-hydroxybutyrate) and cellulose acetate butyrate studied by DSC, FT-IR, and WAXD

Relationships between composition- and temperature-dependent intermolecular interactions and cold crystallization behaviors of poly(3-hydroxybutyrate) (PHB)/ cellulose acetate butyrate (CAB) blends have been investigated mainly by infrared (IR) spectroscopy, together with differential scanning calorimetry, and wide-angle X-ray diffraction (WAXD). Weak intermolecular hydrogen bondings between OH groups in CAB and CO groups in amorphous part of PHB define as inter were detected in OH stretching bands of the blends. These interactions occur in the blends with high CAB content (wCAB) and highly depend on temperature. For all the blends having 0.2≤wCAB≤0.7, when temperature is raised (e.g., above 90°C for the blend with wCAB=0.5) the cold crystallization of PHB was discerned, as evidenced by an increase of the absorbance of the band due to CO stretching in the crystal field. The crystallization was found to involve the dissociation of inter and transformation of inter into intramolecular hydrogen bondings within PHB and within CAB as summarized in Table 2 in this text, which promotes the crystallization and enhances stabilization of the crystals. Consequently, the crystallization of the PHB is influenced by exchanges of the hydrogen bondings as described above with raising temperatures. X-ray diffraction from PHB crystals in the blends show a remarkable decrease of crystallinity with wCAB and eventually disappear when wCAB≥0.8.