Nonisothermal Crystallization Behavior Research Articles

Effect of styrene–butadiene–styrene triblock copolymer on non-isothermal crystallization kinetics and melting behavior of syndiotactic 1, 2-polybutadiene

Syndiotactic 1,2-polybutadiene (s-PB), as a semi-crystalline polymer, has many excellent properties, such as thermal stability and processability. Meanwhile, styrene–butadiene–styrene triblock copolymer (SBS) is an amorphous thermoplastic elastomer. Therefore, modifying s-PB with SBS will affect the crystallization and melting behavior of s-PB/SBS blends. In this work, differential scanning calorimetry technique was used to investigate the effect of the introduction of SBS on non-isothermal crystallization and melting behavior of s-PB. Non-isothermal crystallization kinetics was analyzed by Jeziorny, Ozawa and Mo’s methods. Jeziorny method indicates that the crystallization process can be divided into two stages as primary crystallization and secondary crystallization. Mo’s method gives a better description of the non-isothermal crystallization kinetics of s-PB/SBS blends (the mass ratios are 100/0, 95/5, 90/10, and 80/20). These two methods both indicate that the crystal process becomes difficult with increasing SBS content, but the introduction plays little or no effect on the nucleation mechanism and crystal growth type of s-PB in the bends. Comparatively, Ozawa method is not suitable for this system. The effective energy barriers during the non-isothermal crystallization process are also analyzed via Friedman method.

Investigating the Physical Properties of Poly(L-lactic acid) Modified Using an Aromatics Succinic Dihydrazide Derivative

In order to overcome the defect of slow crystallization rate of Poly(L-lactic acid) (PLLA) during manufacturing, a new organic nucleating agent, N,N'-succinic bis(hydrocinnamic acid) dihydrazide (BHSH), was synthesized to evaluate its influence on the crystallization and other physical properties of PLLA in this work. For this purpose, the non-isothermal crystallization, isothermal crystallization of PLLA modified using BHSH were investigated using differential scanning calorimetry and depolarized-light intensity measurement. Additionally, the melting behavior, thermal stability, and optical property of BHSHnucleated PLLA were further studied. The result of the non-isothermal crystallization behavior indicated that BHSH had a distinct accelerating effect for the melt crystallization process of PLLA and the non-isothermal crystallization peak shifted to the higher temperature and became sharper. Meantime, non-isothermal crystallization result further revealed that both the cooling rate and the final set melting temperature affected the non-isothermal crystallization behavior of PLLA. The addition of BHSH could cause the crystallization halftime of PLLA to become shorter, meaning that PLLA/BHSH samples had a faster overall crystallization rate comparing with the pure PLLA. Upon the addition of 2 wt% BHSH, the crystallization half-time of PLLA/BHSH decreased from 575.7 s to the minimum value 48.6 s at 100°C. Melting behavior after crystallization further confirmed the crystallization promoting effect of BHSH for PLLA, and the double-melting peaks were attributed to the melting-recrystallization. Although that the BHSH could improve the crystallization of PLLA, unfortunately, the presence of BHSH decreased the thermal stability and light transmittance of PLLA.

Cationic Cyclopentadienyliron Complex as a Novel and Successful Nucleating Agent on the Crystallization Behavior of the Biodegradable PHB Polymer.

Cationic cyclopentadienyliron (CpFe+) is one of the most fruitful organometallic moieties that has been utilized to mediate the facile synthesis of a massive number of macromolecules. However, the ability of this compound to function as a nucleating agent to improve other macromolecule properties has not been explored. This report scrutinizes the influence of the cationic complex as a novel nucleating agent on the spherulitic morphology, crystal structure, and isothermal and non-isothermal crystallization behavior of the Poly(3-hydroxybutyrate) (PHB) bacterial origin. The incorporation of the CpFe+ into the PHB materials caused a significant increase in its spherulitic numbers with a remarkable reduction in the spherulitic sizes. Unlike other nucleating agents, the SEM imageries exhibited a good dispersion without forming agglomerates of the CpFe+ moieties in the PHB matrix. Moreover, according to the FTIR analysis, the cationic organoiron complex has a strong interaction with the PHB polymeric chains via the coordination with its ester carbonyl. Yet, the XRD results revealed that this incorporation had no significant effect on the PHB crystalline structure. Though the CpFe+ had no effect on the polymer’s crystal structure, it accelerated outstandingly the melt crystallization of the PHB. Meanwhile, the crystallization half-times (t0.5) of the PHB decreased dramatically with the addition of the CpFe+. The isothermal and non-isothermal crystallization processes were successfully described using the Avrami model and a modified Avrami model, as well as a combination of the Avrami and Ozawa methods. Finally, the effective activation energy of the PHB/CpFe+ nanocomposites was much lower than those of their pure counterparts, which supported the heterogeneous nucleation mechanism with the organometallic moieties, indicating that the CpFe+ is a superior nucleating agent for this class of polymer.

Nonisothermal Crystallization Kinetics of Glassy Mold Fluxes

Crystallization of the solid glassy mold flux film occurring in the gap between the initial shell and mold wall is important, as it determines the in-mold heat transfer and mold lubrication during the process of continuous casting. In order to study the nonisothermal crystallization behavior of the glassy mold flux film in the continuous casting mold, the continuous heating transformation diagram, crystallization mechanism, and precipitate phases were investigated using the single hot thermocouple technique, kinetic models, a scanning electron microscope, and an energy-dispersive spectrometer (EDS). The results show that the initial crystallization temperature for CaO-SiO2 based flux A ranges from [1086 K to 1147 K (813 °C to 874 °C)], which is lower than the case of CaO-Al2O3 based flux B ranging from [1205 K to 1245 K (932 °C to 972 °C)]. The crystallization kinetics for flux A are constant nucleation rate, two-dimensional growth, and control by diffusion. For flux B, they are constant nucleation rate, three-dimensional growth, and control by interface reaction. Besides, the EDS results indicate that the precipitate crystals in fluxes A and B are CaSiO3 and Ca2AlSiO4, respectively.

Effect of low loadings of cellulose nanocrystals on the significantly enhanced crystallization of biodegradable poly(butylene succinate-co-butylene adipate)

Biodegradable poly(butylene succinate-co-butylene adipate) (PBSA)/cellulose nanocrystals (CNC) nanocomposites were successfully prepared via a solution and casting method at low CNC loadings. The nonisothermal and isothermal melt crystallization behaviors of PBSA/CNC nanocomposites were significantly enhanced by low loading of CNC. The nonisothermal melt crystallization peak temperature obviously increased from 56 °C for neat PBSA to 63.6 °C for PBSA/CNC1 (the nanocomposite containing 1 wt% CNC) at 10 °C/min. Crystallization half-time at 80 °C significantly decreased from 31 min for neat PBSA to 8.4 min for PBSA/CNC1. CNC apparently increased the crystallization rate of PBSA; however, the crystallization mechanism remained unchanged. The crystalline morphology study verified the enhanced nucleation density of PBSA spherulites, indicating the role of CNC as an efficient nucleating agent. In addition, low loadings of CNC did not modify the crystal structure of PBSA.

Non-isothermal crystallization of copper-containing composite based on polymer alloy of poly(ethylene oxide) and polyethylene

Non-isothermal crystallization behavior of copper/poly(ethylene oxide)/low density polyethylene (Cu/PEO/LDPE) composite was investigated by using differential scanning calorimetry, and the feasibility of various models for determination the non-isothermal crystallization kinetics and activation energy of its LDPE matrix were evaluated in this work. The results show that the crystallization of its LDPE matrix was retarded by the addition of PEO with a higher molecular weight and accelerated by cooling with a larger cooling rate. The results also show that the crystallization kinetics of the LDPE matrix was not affected by the PEO molecular weights, but the crystallization activation energy of the LDPE matrix was affected and increases with the increase of PEO molecular weight. Additionally, Avrami-Ozawa equation is desirable to determinate the non-isothermal crystallization kinetics of their LDPE matrix, and isoconversional method modified by Vyazovkin is more suitable to calculate the non-isothermal crystallization activation energy of their LDPE matrix.

On crystallization and oxidation behavior of Zr54Cu46 and Zr27Hf27Cu46 thin-film metallic glasses compared to a crystalline Zr54Cu46 thin-film alloy

Amorphous Zr54Cu46 and Zr27Hf27Cu46 thin-film metallic glasses were prepared by non-reactive magnetron co-sputtering of Zr, Hf and Cu in pure argon. Several as-deposited Zr54Cu46 films were post-annealed in high vacuum to create a crystalline thin-film alloy of the identical composition. The non-isothermal crystallization behavior of the amorphous Zr54Cu46 and Zr27Hf27Cu46 films and the effect of a substitution of Hf for Zr on the crystallization process were studied by differential scanning calorimetry. The activation energy of the crystallization was obtained by the Kissinger–Akahira–Sunose method. The results show that the activation energy of the Zr27Hf27Cu46 film was higher for all conversion fractions, which indicates that the substitution of Hf for Zr enhances the thermal stability of the glassy state. Considerable attention was also paid to the isothermal oxidation behavior of the amorphous and crystalline Zr54Cu46, and amorphous Zr27Hf27Cu46 films investigated by thermogravimetric analysis. It was shown that all oxidation curves in the temperature range from 400 to 575 °C obeyed the parabolic law. The activation energy of the oxidation process determined by the Arrhenius equation for the oxidation rate constants was found to be the highest for the Zr27Hf27Cu46 film, which indicates that its surface oxide layer is a more effective barrier against the diffusion of species.

Non-isothermal crystallization behavior of polyethylene glycol/expanded vermiculite form-stable composite phase change material

In this work, non-isothermal crystallization behavior of polyethylene glycol (PEG)/expanded vermiculite (EVM) form-stable composite phase change material (PEG-EVM) was investigated. The activation energy of non-isothermal crystallization of PEG-EVM (−219.7 kJ/mol) was lower than that of PEG (−375.3 kJ/mol), indicating that the energy barrier of heterogeneous nucleation decreased, demonstrating that the EVM significantly accelerated the nucleation of PEG. However, the crystallization kinetic parameters (half-crystallization time, crystallization rate and required cooling rate for a designated relative crystallinity) revealed that the non-isothermal crystalline growth of PEG in PEG-EVM was constrained because the surface interactions of EVM hindered the migration and diffusion of PEG molecular chains to the surface of nucleus.

Isothermal and non-isothermal crystallization kinetics of composites of poly(propylene) and MWCNTs

The isothermal and non-isothermal crystallization behaviour of composites of a poly(propylene) (PP) and multi-walled carbon nanotubes (MWCNTs) were investigated using Differential Scanning Calorimetry (DSC). An Avrami analysis was used to study the isothermal crystallization kinetics of unfilled PP and composites of PP with MWCNT loadings up to 2 (w/w). The value of the Avrami exponent (n) was greater than 2 for all samples, confirming the primary stage of crystal growth is a three-dimensional phenomenon. The activation energy (ΔE), determined using an Arrhenius type expression, for the isothermal crystallization of PP increased from 87 kJ for unfilled PP to 228 kJ on incorporation of 2 (w/w) MWCNTs to PP. An attempt was made to model the non-isothermal crystallization kinetics of composites of PP and MWCNTs using a range of mathematical models, including the Jeziorny extended Avrami equation, Ozawa equation, Caze and Chuah average Avrami exponents, and a combined Avrami/Ozawa approach. The Jeziorny extended Avrami approach confirmed that the non-isothermal crystallization of MWCNT filled PP is clearly a two-stage process. Fitting of the Ozawa model was shown to be not valid and both the Caze and Chuah average Avrami approaches were ineffective as neither took in to account the effects of secondary crystallization. Only the combined Avrami/Ozawa method successfully modelled the two-stage crystallization of composites of PP and MWCNTs. The activation energy (ΔE) for the non-isothermal crystallization of PP on addition of MWCNTs increased with increasing MWCNT content, up to as high as 726 kJ.

Thermal behavior and light transmittance of PLLA nucleated using strontium phenylmalonate

Adding functional additives in the poly(l-lactic acid) (PLLA) matrix to develop high-performance modified biodegradable polymers is of great interest. Therefore, in this work, strontium phenylmalonate (SrPA), as an organic–inorganic hybrid material, was prepared through a neutralization reaction to evaluate its influence on the crystallization behavior, melting behavior, thermal stability and light transmittance of PLLA. The non-isothermal crystallization behavior, for all PLLA/SrPA samples, showed that the SrPA loading and variations in cooling rate significantly influenced the non-isothermal crystallization of PLLA; 5 wt% SrPA exhibited the best crystallization-accelerating capability for PLLA. However, the effects of the set final melt temperature used on the non-isothermal crystallization were negligible, resulting from the minimal difference in solubility of SrPA in the PLLA matrix in the temperature range of 170–210°C. The results from X-ray diffraction measurements and melting behavior further demonstrated the crystallization-accelerating role of SrPA for PLLA. Thermal stability measurements indicated that the incorporation of SrPA did not change the thermal decomposition behavior of PLLA, but the onset decomposition temperature decreased with increasing SrPA concentration. The addition of SrPA led to a significant decrease in light transmittance.

Investigation on the modification of N,N′-adipic bis(benzoic acid) dihydrazide on poly(l-lactic acid)

In this study, poly(l-lactic acid) (PLLA) modified using N,N′-adipic bis(benzoic acid) dihydrazide (BAAD) was fabricated by melt blending technology, and the differential scanning calorimetry, optical depolarizer, and thermogravimetric analysis (TGA) evaluated the effects of BAAD on crystallization behavior, melting behavior, and thermal stability of PLLA. Non-isothermal crystallization behavior indicated that BAAD as a heterogeneous nucleating agent had excellent acceleration effectiveness on the melt crystallization process of PLLA; however, an increase in cooling rate weakened the crystallization promoting effect of BAAD for PLLA, resulting from increasing cooling rate which led to decrease in the nuclei density. Additionally, non-isothermal crystallization results revealed that the effect of the final melting temperatures on the crystallization peak temperature and crystallization enthalpy was negligible. Isothermal crystallization measurement showed that the minimum t1/2 of the primary PLLA appeared at 120 °C, but the PLLA/2%BAAD exhibited the shortest t1/2 of 33.9 s at 95 °C comparing to the primary PLLA and other PLLA/BAAD samples. Through the analysis of the frontier molecular orbital energy and thermal stability of PLLA/BAAD system, it was proposed that the nucleation mechanism of the PLLA/BAAD system was chemical nucleation. Melting behavior of PLLA/BAAD system further confirmed the crystallization accelerating effect of BAAD for PLLA, as well as that the melting behavior of a given sample after non-isothermal crystallization was almost not dependent upon the heating rates, but the melting peak after isothermal crystallization shifted toward the higher temperature with the increase in crystallization time. Finally, the results of TGA measurements indicated that BAAD could not change the thermal decomposition profile of PLLA, but the concentration of BAAD could affect the onset decomposition temperature of PLLA.

Screening of sugar alcohols and their binary eutectic mixtures as phase change materials for low-to-medium temperature latent heat storage. (Ⅰ): Non-isothermal melting and crystallization behaviors

Towards latent heat storage in the low-to-medium temperature range (70–250 °C), screening of sugar alcohols and their binary eutectic mixtures as potential phase change materials was carried out by focusing on the non-isothermal melting and crystallization behaviors. A preliminary screening shortened the long list of isomers from common four-carbon to six-carbon sugar alcohols to only six affordable candidates, i.e., xylitol, d-sorbitol, erythritol, d-mannitol, d-dulcitol and inositol (ordered with increasing the melting point). Based on the six pre-screened sugar alcohols, a total of 15 binary eutectic mixtures were prepared to manipulate the melting points for more flexible match with real applications. Non-isothermal tests were then performed on a differential scanning calorimeter at various ramping/cooling rates up to 10 °C/min. In addition to determination of the melting point and latent heat of fusion, a special attention was paid to the crystallization behaviors by undertaking consecutive melting-crystallization cyclic tests. It was found that the two candidates with the lowest melting points (both below 100 °C), i.e., xylitol and d-sorbitol, as well as the nine binary eutectic mixtures containing at least one of them, are unable to crystallize from the melt during cool-down at any cooling rates tested (down to 0.5 °C/min). Four other binary eutectic mixtures, i.e., erythritol (84 mol%) + d-mannitol, erythritol (95 mol%) + d-dulcitol, erythritol (96 mol%) + inositol and d-dulcitol (69 mol%) + inositol, were also shown to be unable to crystallize upon cooling, with the crystallization occurring during the reheating process instead, referred to as cold crystallization. The rest four pure sugar alcohols with relatively high melting points (110–230 °C), i.e., erythritol, d-mannitol, d-dulcitol, inositol, and two mixtures, i.e., d-mannitol (70 mol%) + d-dulcitol and d-mannitol (82 mol%) +inositol, were found to be able to crystallize upon cooling, although they all suffer from severe supercooling (e.g., up to over 100 °C for erythritol). The affordable pure and mixture sugar alcohols were deemed to have desirably high latent heat storage density, especially for those with higher melting points. However, they all face specific issues associated with crystallization, which must be addressed before they can really be utilized in real applications. In addition, it may not worth making eutectic mixtures, although this is deemed to be an effective way of manipulating the melting points of sugar alcohols.

Glass Forming Ability and Crystallization Kinetics of Cu-Zr-Al-(Y, Ag) Amorphous Alloy

Cu-Zr-Al-(Y, Ag) amorphous alloy ribbons of Cu50Zr42Al8, Cu46Zr47-xAl7Yx(x=2, 5), Cu43Zr42Al8Ag7, and Cu43Zr42Al8Ag5Y2 were prepared using the single roller melt-spinning method. The glass forming ability and non-isothermal crystallization behavior of the amorphous alloys were investigated by means of X-ray diffraction (XRD) and differential scanning calorimetry (DSC) in a continuous heating mode. The experimental results show that the glass forming ability and thermal stability of Cu-Zr-Al amorphous alloys are improved by adding minor amounts of Y and Ag, and the effect of Ag on the glass forming ability is more significant than that of Y. Compared to the Cu50Zr42Al8 alloy, the width of the supercooled liquid region of the Cu46Zr47-xAl7Yx(x = 2 and 5) alloys increased by 19 K and 30 K, respectively. The reduced glass transition temperature (Trg) and the parameter γ of the two alloys enhanced separately. Compared to the Cu50Zr42Al8 alloy, the Trg and γ values of both Cu43Zr42Al8Ag7 and Cu43Zr42Al8Ag5Y2 alloys enhanced noticeably up to 0.619, 0.417, and 0.609, 0.412, respectively. The crystallization activation energies of the amorphous alloys calculated by the Kissinger and Flynn Wall Ozawa equations increased with the addition of minor Y and Ag into the Cu50Zr42Al8 alloy. The addition of Y and Ag significantly improved the thermal stability of the Cu50Zr42Al8 amorphous alloy.

Thermal degradation behaviour and crystallization kinetics of poly (lactic acid) and cellulose nanocrystals (CNC) based microcellular composite foams

The current investigation addresses the thermal degradation and non-isothermal crystallization behaviour of the fabricated poly (lactic acid) foam (nPLA) and poly (lactic acid) (PLA)/cellulose nanocrystal (CNC) based foams at three different loadings of CNC (i.e. 1%, 2% and 3%) as PLA/CNC 1, PLA/CNC 2 and PLA/CNC 3 having highly porous, interconnected and microcellular morphology. The formation of various gaseous products at two different conversions (α = 0.3 and α = 0.7) are investigated by using thermogravimetric analyser hyphenated Fourier transmission infrared spectroscopy (TGA-FTIR) analysis in isothermal condition. Effect of porosity and CNC reinforcement towards thermal degradation and crystallization of the PLA is thoroughly investigated by using mercury intrusion porosimetry (MIP). “Model-free” and “modelistic” approaches like Friedman, Flynn-Wall-Ozawa (FWO), Kissinger-Akahira-Sinouse (KAS), Kissinger and Augis & Bennet have been utilized for non-isothermal degradation kinetics of the fabricated foams. Non-isothermal melt crystallization kinetics of fabricated foams reveals that both primary and secondary crystallization process taking place. The apparent activation energy calculated from FWO are ~175.8 kJ/mol, ~198.6 kJ/mol, ~175.5 kJ/mol and ~174.7 kJ/mol for nPLA, PLA/CNC 1, PLA/CNC 2 and PLA/CNC 3 respectively. It is also observed that at higher conversions, complex three dimensional diffusion mechanism of degradation might be taking place in accordance with Criado plots.

Rheology, Non-Isothermal Crystallization Behavior, Mechanical and Thermal Properties of PMMA-Modified Carbon Fiber-Reinforced Poly(Ethylene Terephthalate) Composites.

Poly(ethylene terephthalate) (PET) composites containing carbon fiber (CF) or polymethyl methacrylate (PMMA)-grafted carbon fiber (PMMA-g-CF) were prepared by melt compounding. The rheology, non-isothermal crystallization behavior, and mechanical and thermal properties of pure PET, PET/CF and PET/PMMA-g-CF composites were investigated. The results show that the addition of CF or PMMA-g-CF significantly increases the storage modulus (G′), loss modulus (G″), and complex viscosity (η*) of the composites at low frequency. The Cole-Cole plots confirm that the surface modification of CF leads to a better interaction between the CF and PET, and then decreases the heterogeneity of the polymeric systems, which is confirmed by the SEM observation on the tensile fracture surface of the composites. Non-isothermal crystallization analysis shows that the CF or PMMA-g-CF could serve as nucleation agent to accelerate the crystallization rate of the composites, and the effect of PMMA-g-CF is stronger than that of CF. The result is further confirmed by the analysis of the crystallization activation energy for all composites calculated by the Flynn-Wall-Ozawa method. Moreover, the tensile and impact strength and the thermal stability of the composites are improved by CF, while the incorporation of PMMA-g-CF further enhances the tensile and impact strength and thermal stability.

Effect of content and particle size of talc on nonisothermal melt crystallization behavior of poly(l-lactide)

This work examined the effect of content and particle size of nucleating agent on nonisothermal melt crystallization behavior of poly(l-lactide) (PLLA). Two different particle sizes of talc were used as the nucleating agents of PLLA. Scanning electron microscopy observation revealed that both big and small particles of talc were homogeneously dispersed in the PLLA matrix. Talc significantly accelerated the nonisothermal melt crystallization rate of PLLA. The effect of smaller particle talc on crystallization was obviously better than that of the bigger one. The activation energy based on Friedman equation was evaluated. Lower activation energy was obtained for nucleated PLLA. Finally, addition of talc did not modify the crystal structure.

Crystallization of Poly (Lactic Acid), PLA: Effect of Nucleating Agents and Structure-Properties Relationships

In this paper, a brief state of the art is given firstly on structure-processing-properties relationships on PLA. Secondly, a specific focus is devoted on some recent and not yet unpublished recent work regarding the isothermal and non-isothermal crystallization behaviors of the poly (lactic acid). Thereby, they were investigated by differential scanning calorimetry. The effect of heterogeneous nucleation was assessed by additive talc, ethylenebis (12- hydroxy stearyl amide) (EBHSA) and polyethylene glycol (PEG) as potential nucleating agents. Thus, the improvement of crystallization kinetics under isothermal crystallization was described by the Avrami equation. A new formulation system can be used as a nucleating agent. This system consists of (1% wt talc, 1% wt PEG and x% wt EBHSA), “x” is equal to 1, 3 and 5%. Startling, Its increase the crystallization rate of pure PLA and reduce drastically its half-time of crystallization. Hence, the obtained results are for the great interest of some biopolymer processing as well injection molding or extrusion.

The Effect of Maleated Polypropylene on the Non-Isothermal Crystallization Kinetics of Wood Fiber-Reinforced Polypropylene Composites.

The influence of maleated polypropylene (MAPP) on the non-isothermal crystallization behavior of wood fiber (WF)-reinforced PP composites (WPCs) was investigated by a differential scanning calorimeter (DSC). The results showed that MAPP as a nucleation agent accelerated the crystallization rate of the PP matrix in WPC under the cooling process. The corresponding crystallization kinetics and activation energy were further analyzed using the Avrami method, Avrami–Ozawa method, Kissinger method, and Friedman method. The results demonstrated that MAPP significantly changed the crystal growth mechanism of the PP matrix to heterogeneous nucleation for acicular and tabular crystal growth during the annealing step. A remarkably lower cooling rate can achieve a certain relative crystallinity degree at the unit crystallization time for WPC with 3 wt % MAPP (WPCM3). Similarly, the lowest crystallization activation energy was observed for the WPCM3 among all WPCs by the Kissinger method. Furthermore, based on the Friedman method, the addition of MAPP easily caused the PP matrix to crystallize in the WPC at the initial stage of relative crystallinity.

Nucleated Poly(l-lactic acid) with N, N′-oxalyl bis(benzoic acid) dihydrazide

One of the major challenges in the field of Poly(l-lactic acid) (PLLA) is the enhancement of crystallization. In the present work, the evaluation of the influence of N, N′-oxalyl bis(benzoic acid) dihydrazide (TBOD), as a novel organic nucleating agent, on the non-isothermal crystallization, melting behavior, and thermal stability of PLLA was performed using differential scanning calorimeter and thermogravimetric analysis. Non-isothermal crystallization measurement revealed that TBOD had an excellent accelerating effect for the crystallization of PLLA in cooling, and upon the addition of 3 wt% TBOD, PLLA exhibited the highest onset crystallization temperature and the crystallization peak temperature, as well as the largest non-isothermal crystallization enthalpy. In particular, when the TBOD concentration was 1 wt% ∼ 3 wt%, the onset crystallization temperatures were higher than the theoretical ceiling temperature of crystallization, thoroughly demonstrating the powerful crystallization promoting ability of TBOD. Additionally, the non-isothermal crystallization behavior of PLLA/TBOD depended on the TBOD concentration, cooling rate as well as the final melting temperature. The melting behavior of PLLA/TBOD after non-isothermal crystallization further confirmed the effect of TBOD on the crystallization process and crystal structure of PLLA, and the appearance of the double melting peaks during melting stages was attribute to the melting-recrystallization. For melting behavior after isothermal crystallization, the crystallization temperature and crystallization time significantly affected the melting behavior of PLLA/TBOD. The addition of TBOD could not change the thermal decomposition profile of the PLLA, but the thermal stability did not regularly decrease with increasing of TBOD concentration, indicating that there might exist intermolecular interaction between PLLA and TBOD.

Influence of high molecular weight poly(ethylene adipate) on the crystallization behavior and mechanical properties of biodegradable poly(l-lactide) in their immiscible polymer blend

A fully biodegradable polymer blend consisting of poly(l-lactide) (PLLA) and poly(ethylene adipate) (PEA) with relatively high number average molecular weight of 8000 g/mol (80/20 in weight ratio) was prepared through a solution and casting method. The dynamic mechanical analysis and scanning electron microscopy studies confirmed that PLLA was immiscible with PEA. The crystallization behavior, crystal structure and mechanical properties of PLLA/PEA blend were investigated and compared with those of neat PLLA. In the immiscible blend, the blending with PEA enhanced the nonisothermal cold and melt crystallization behavior, decreased the isothermal melt crystallization rate and retained the crystallization mechanism and crystal structure of PLLA. The tensile test results revealed that the ductility and toughness of PLLA phase were significantly improved by the blending with high molecular weight PEA.