Crystallizable Fraction Research Articles

Revealing time-dependent behavior of asphalt binder at low-temperature by crystallization kinetics

To gain deeper insights into the influence of thermal history on wax crystallization and thermoreversible aging for enhanced asphalt pavement durability, this study employed the extended bending beam rheometer (ExBBR) test and modulated differential scanning calorimetry (MDSC) analysis. These techniques were utilized to analyze the crystallization kinetics of diverse asphalt binders under both isothermal and non-isothermal conditions. The ExBBR test results demonstrated that the cold-temperature performance of asphalt binders experiences continuous degradation with an increasing grade loss during conditioning. The Avrami isothermal crystallization kinetic theory proved to be an accurate descriptor of the thermoreversible aging tendency in asphalt binders. MDSC test findings revealed that distinct cooling rates exert an influence solely on specific asphalt varieties, with discrepancies in thermal signals arising from diverse oil sources. The Ozawa exponent, determined through the endothermic background area selected from the baseline, serves as a reliable guide for assessing the degree of thermoreversible aging in different asphalt binders. Crucially, the appearance of crystallizable fractions in asphalt binders with varying thermal histories can be effectively modeled using both isothermal Avrami and non-isothermal Ozawa theoretical frameworks. To conclude, the study undertook the separation of four components of asphalt, analyzing the microstructural evolution of these components under identical test conditions. The contribution of each component to the asphalt crystallization process is comprehensively expounded through considerations of glass transition temperatures, as well as endothermic and exothermic peaks associated with distinct components.

Experimental study on the effect of molecular weight and chemical composition distribution on the mechanical response of high‐density polyethylene

AbstractThis article aims to appraise the effect of microstructure comprising molecular weight distribution and chemical composition distribution on the mechanical properties of high‐density polyethylene (HDPE). HDPE resins were synthesized using several titanium–magnesium‐supported Ziegler–Natta catalysts in the industrial gas phase reactor under the same polymerization condition. Gel permeation chromatography and crystallization elution fractionation (CEF) were conducted on the resins to characterize the molecular weight and comonomer distribution. Crystallization, thermal and rheological behavior were evaluated following differential scanning calorimetry, polarization light microscopy, and rheometric mechanical spectrometry. The resins with higher soluble fraction in trichlorobenzene below 80°C (highly branched low molecular weight chains) exhibited longer crystallization time based on the crystallization kinetic obtained from the Avrami model. Rheological determination of the molecular weight between entanglements (Me) and the average lamella thickness based on the Gibbs–Thomson equation revealed that the entanglement density and impact strength decreased, and the average lamella thickness increased with an increase in the ratio of CEF eluted fraction below 80°C to the crystallizable fraction in the range of 80–90°C.

Biodegradable binary blends of poly (butylene succinate) or poly (ε-caprolactone) with poly (butylene succinate-ran-ε-caprolactone)copolymers: Crystallization behavior

Poly (butylene succinate) (PBS) and polycaprolactone (PCL) are two immiscible biocompatible and biodegradable polymers. Aiming to combine the properties of these biodegradable polymers, this work explores for the first time blending PBS or PCL with PBS-ran-PCL copolymers (BSxCLy) at 75/25, 50/50, and 25/75 wt% compositions, with various copolymer contents: BS78CL22, BS46CL54, and BS15CL85. The crystallization behavior of these novel binary blends was systematically studied with non-isothermal and isothermal differential scanning calorimetry (DSC), polarized light optical microscopy (PLOM), and simultaneous wide- and small-angle X-ray scattering (WAXS and SAXS). All the blends displayed a miscible character in the amorphous state, judging by a single glass transition temperature, and in the melt state (as indicated by SAXS), but their miscibility in the crystalline state depends on the specific blend. In both PBS/BS78CL22 and PCL/BS15CL85 evidences of co-crystallization between the matrix and the crystallizable fraction of the copolymer were found. However, high comonomer exclusion, higher in the BS15CL85 than in the BS78CL22, greatly affects blend miscibility. Thus, the results show that the PBS/BS78CL22 blend is miscible, in the crystalline state, at high PBS (homopolymer) content, i.e., 75/25 and 50/50 compositions, whereas its “counterpart”, the PCL/BS15CL85 displays partial miscibility, even for high PCL (homopolymer) content. For the 25/75 blends, i.e., copolymer-rich, the homopolymer addition favors the crystallization of the copolymer-rich component. Blending PBS or PCL with BS46CL54 leads to blends that exhibit a much lower miscibility in the crystalline state than the blends prepared with BS or CL-rich copolymers, independently of the composition. But, interestingly, a novel behavior is found, since the BS46CL54 copolymer can crystallize either in PBS type crystals or in PCL type crystals depending on the polymeric matrix (PCL or PBS). The PBS favors the crystallization of the BS component, while the PCL favors the crystallization of the CL component within the random copolymer. The crystallization behavior found in this work evidences the interactions of the PBS or PCL with the BSxCLy copolymer, representing a potential strategy to combine the properties of the PBS and PCL through blending.

An experimentally validated model for quiescent multiphase primary and secondary crystallization phenomena in PP with low content of ethylene comonomer

While crystallization behavior of isotactic polypropylene homopolymers had been subject to a wide range of experimental and modeling studies, this is not the case for propylene-ethylene random copolymers (PPR). This class of polymers offers up to now significant challenges, both from an experimental as well as a modeling perspective. The ethylene incorporation in the propylene chains, as well as the distribution of this comonomer, has a marked effect on the crystallization kinetics. Moreover, the presence of these defects causes a clear separation between primary crystallization (i.e. space filling) and subsequent secondary crystallization (increase of crystallinity in filled space) within the spherulitic skeletons, particularly subsequent at high primary crystallization temperatures. In this work, the underlying mechanism is first quantified by means of a combination of in-situ WAXD and SAXS experiments, as well as ex-situ WAXD experiments and calorimetric measurements. Based on these experiments an extended model framework is presented, capable of predicting multiphase non-isothermal crystallization kinetics as well as the final crystallinity as a function of the applied thermal conditions relevant for processing. The chemical composition distribution (CCD) of the ethylene comonomer serves as critical input to parameterize the model. Optical microscopy- and DSC experiments are used for parameterization of the primary crystallization model. The model developed in this study is, in principle, applicable to all polypropylenes, ranging from homo-polymers to random copolymers with variable comonomer content and/or CCD but, so far, only applied and validated on one PPR. To validate the model and the parameters for a given PPR, several non-isothermal and isothermal experiments (the latter followed by subsequent cooling) are conducted over a wide range of crystallization temperatures and cooling rates. The good match between experiments and model predictions demonstrates the power of the newly developed framework. The final crystallinity, the amount of α - and γ -phase, and the ratio between primary and secondary crystallization can be predicted as a function of the time-temperature history. To the best knowledge of the authors, it is the first time that such a direct connection with the CCD is incorporated in a crystallization model. Consequently, the model offers a new tool to bridge the gap between chemical structure and resulting product properties, which now has come one step closer for PPR systems. • Isothermal and cooling experiments reveal primary and secondary crystallization behavior of PPR. • Primary crystallization is modeled via formation of α-skeletons, in which γ-phase co-crystallizes. • Incorporated multi-phase secondary crystallization to predict final phase composition. • Final crystallinity from the introduction of a crystallizable fraction and kinetic maximum. • Direct link between chemical composition distribution and crystallization kinetics.

Application of Antibody Fragments Against Aβ With Emphasis on Combined Application With Nanoparticles in Alzheimer's Disease.

Alzheimer’s disease (AD) is one of the most common neurodegenerative diseases and accumulating evidences suggest a key role of amyloid-β (Aβ) peptide in the pathogenesis of AD. According to the amyloid cascade hypothesis, the imbalance of producing and clearing Aβ is the beginning of neurodegeneration and dementia. Consequently, immunotherapy becomes popular through using antibodies against Aβ. However, many studies of monoclonal antibodies were stopped because adverse effects appeared or there were no evident benefits observed. Some antibody fragments have many advantages over monoclonal antibodies, such as small sizes, lack of the crystallizable fraction (Fc) and so on. There are three main antibody fragments, including single chain variable fragments (scFvs), Fab fragments and single-domain antibody fragments. Nanoparticles can facilitate the entry of drug molecules across the blood-brain barrier, making them become excellent carriers. Various kinds of nanoparticles have been applied in the treatment of AD. The combination of nanoparticles and antibody fragments against amyloid-β can be used in the diagnosis and treatment of Alzheimer’s disease. In this review, we summarize the progress of antibody fragments against amyloid-β in AD, focusing on the combined application with nanoparticles in the diagnosis and treatment of AD.

Modulated differential scanning calorimetry study of wax-doped asphalt binders

In order to better understand how wax constituents affect thermoreversible aging phenomena, three kinds of n-alkanes were doped into a base asphalt binder. Modulated differential scanning calorimetry (MDSC) analysis was performed on a series of binders containing increasing wax contents. It was discovered that the addition of n-alkanes not only changes the non-reversible thermal signal but also the reversible one. For asphalt doped with n-C20, the thermal behavior shows significant time-dependent behavior, while those doped with n-C32 and n-C40 do not. The size of both endothermic peaks in the total heat flow and non-reversible heat flow curves decreases with oxidation of wax-doped asphalt binders. The appearance of crystallizable fractions in wax-doped asphalt binders with varying thermal history can be modeled in both isothermal Avrami and non-isothermal Ozawa theoretical frameworks. A possible mechanism for the thermoreversible aging phenomenon has been proposed but it will need further work for validation and refinement.

Bitumen fractionation: Contribution of the individual fractions to the mechanical behavior of road binders

Anticipation of alternative road binder to replace petroleum derived bitumen requires a deep understanding of relationships between the chemical composition of bitumen and their physical properties, especially rheological ones. The vast number of the different molecules constituting bitumen is too complicated to unravel, thus in this paper we propose to fractionate bitumen into four fractions and study their different physico-chemical properties. The melting temperature and the glass transition of each fractions was determined by DSC while their molecular weight distribution was determined by HS-SEC. Finally, their rheological properties were investigated by DSR. This study highlighted the importance of all bitumen phases: the less polar liquid phase driving the viscous behavior up to −50 °C, the more polar solid phase responsible of the thermal stability and the stiffness, and finally the intermediate viscous oily phases allowing the molecular weight distribution continuity and by consequence allowing to have, on a large temperature range, a viscous liquid behavior at high temperature or low frequency, and an elastic stiff behavior at low temperature. Crystallizable fractions and asphaltene aggregates seemed to act as key molecular structures in the continuous phase.

Variable-temperature Fourier-transform infrared spectroscopy study of wax precipitation and melting in Canadian and Venezuelan asphalt binders

Variable-temperature Fourier-transform infrared (FTIR) spectroscopy was used to improve our understanding of chemical and physical properties of importance to gradual, thermoreversible aging in asphalt at cold temperatures. The FTIR peak area growth between 735 and 715 cm−1 follows a straight line upon cooling. Abrupt and significant changes in slope signify wax precipitation onset temperatures (WPT). Cold conditioning increased wax melt out temperatures (WMT), while chemical oxidation increased both WMT and WPT. Thermoreversible aging in an extended bending beam rheometer (EBBR) protocol shows Cold Lake, Alberta, and Laguna, Venezuela binders performing exceptionally well, likely because they are very low in crystallizable fractions (CF).

Non-isothermal low-temperature reversible aging of commercial wax-based warm mix asphalts

ABSTRACT Low-temperature reversible aging is one of the most important forms of asphalt hardening, especially for cold regions. However, there are few researches about the influence of wax-based warm additive on the low-temperature reversible aging of asphalt, especially under non-isothermal conditioning. For this reason, simplified extended bending beam rheometer (Ex-BBR) test, non-isothermal rheological analysis and differential scanning calorimetry (DSC) test are performed on asphalt binders containing selected four kinds of commercial wax modifiers (Fischer-Tropschbased wax, linear aliphatic hydrocarbon-based wax, polyethylene-based wax, and fatty acid amides based wax). The results show that all commercial waxes used in this study will accelerate the degree of physical hardening in unaged asphalt binders. Compared with wax-based warm mix additive, oxidative aging has a greater impact on the low-temperature reversible aging properties of asphalt binder. Independent of cooling rate, the base asphalt has the highest phase angle value while the F–T wax modified asphalt has the lowest value. The crystallizable fraction increases with the decrease of cooling rate for both unaged and PAV aged sample. The magnitude of Ozawa exponent has the same order as grade loss for PAV aged sample. However, no obvious rule is observed for unaged asphalt binders.

Epoxy-based paints from glycolysis products of postconsumer PET bottles: synthesis, wet paint properties and film properties

Glycolysis of waste polyethylene terephthalate (PET) flakes obtained from grinding postconsumer bottles was carried out at 180–190°C, and molar ratios of PET/EG were taken as 1/6. Reaction product was extracted by hot water, and water soluble crystallizable fraction and water insoluble fraction were obtained. These fractions were characterized by hydroxyl value determination. Water soluble crystallizable fraction obtained from glycolysis product was used for synthesis of PET-based epoxy resin. Two epoxy-based paints were prepared using different amounts of PET-based epoxy resin. Wet paint properties, and chemical and physical film properties of paints containing waste PET were determined. Increasing the rate of PET-based epoxy resin in paint formulation did not have a negative effect on the wet paint properties and dry film properties of epoxy-based paints containing waste PET.

Rheological characterization of polypropylene/poly(ethylene-co-propylene) in-reactor blends synthesized under different polymerization conditions

In-reactor blends of polypropylene/poly(ethylene-co-propylene) with complex microstructure, synthesized through different polymerization procedures; two-step (one homopolymerization and one copolymerization under high ethylene concentration) and three-step (with an additional copolymerization step under low ethylene concentration), were characterized by rheological measurements. The effects of a change in the polymerization process on the types and amounts of block copolymers in the blends were evaluated using small amplitude oscillation rheometry in the linear viscoelastic region. The Palierne model in its complete form was employed to model the rheological behavior of the blends. For this analysis the reactor products were separated into xylene cold insoluble (XCI) and xylene cold soluble fractions. Besides, another two copolymer fractions at 80 and 100 °C, which are crystallizable copolymer fractions and contain block copolymers rich in polyethylene and polypropylene, respectively, were separated from XCI fraction by xylene using temperature gradient elution fractionation method. Considering all copolymer fractions as dispersed and the remained fraction (mostly polypropylene) as matrix phase, it was shown that the rheological properties of the blends could not be predicted by Palierne model. It was found that only by considering part of block copolymer fractions having long polypropylene sequences along with polypropylene homopolymer as one phase, the rheological properties of the blends could be predicted by Palierne model. By rheological modeling, it was confirmed that the amounts of copolymers with long polypropylene sequences which are miscible with the matrix are higher in the case of three-step blends and also the elasticity of three-step polymerized blends is higher than two-step polymerized blends.

Synthesis and film properties of epoxy esters modified with amino resins from glycolysis products of postconsumer PET bottles

Glycolysis of waste polyethylene terephthalate (PET) flakes obtained from grinding postconsumer bottles was carried out at 225–250°C and molar ratios of PET/ethylene glycol were taken as 1/1, 1/1.5, 1/5, and 1/10. Reaction product was extracted by hot water for three times and water‐soluble crystallizable fraction and water‐insoluble fraction were obtained. These fractions were characterized by acid and hydroxyl value determinations, differential scanning calorimeter analysis, and 1H‐NMR analysis. Glycolysis product was used for synthesis of PET‐based epoxy resin. This epoxy resin was used to prepare epoxy ester resins having 40% and 50% oil content. Epoxy ester resin having 40% oil content was modified with urea‐formaldehyde and melamine‐formaldehyde resins for synthesis of epoxy ester–amino resin. Physical and chemical film properties of epoxy ester and modified epoxy ester resins were investigated. All the epoxy ester and modified epoxy ester films were having excellent adhesion, water, and salt water resistance properties. Modification of PET‐based epoxy ester resins with amino resin has significantly improved hardness, impact resistance, and alkaline and acid resistance of resin films. As a result, PET oligomers obtained from glycolysis of postconsumer PET bottles are suitable for manufacturing of amino‐resin‐modified epoxy ester resins that have improved physical and chemical surface coating properties. POLYM. ENG. SCI., 55:2519–2525, 2015. © 2015 Society of Plastics Engineers

Importance of thermal gradient in the bitumen bees genesis

Bitumen can be regarded as a complex colloidal suspension. Indeed, the heaviest molecules in bitumen, the asphaltenes, are known to self-associate to form solid particles suspended in a fluid called maltenes. Bitumen is also composed of a crystallizable fraction that partitions between asphaltenes and maltenes. This complex colloidal system exhibits peculiar patterns at their surface called “bees.” By varying the bitumen formulation and also tuning process parameters such as the temperature cooling rate, we demonstrate the role of the various components: asphaltenes, maltenes, and the crystallizable fraction on the bee existence and we evidence that the bee formation results from a complex coupling between different physico-chemical phenomena such as phase separation, crystallization, and buckling. We then propose a mechanism of bee genesis based on the thermal properties of the various fractions and especially on the heat capacity of both asphaltenes and maltenes. We demonstrate that a thermal gradient in the sample is required for the formation of bees and put into evidence the importance of kinetic aspects. We also discuss the bitumen general bulk properties.

Characteristics of diether‐ and phthalate‐based Ziegler‐Natta catalysts for copolymerization of propylene and ethylene and terpolymerization of propylene, ethylene, and 1‐butene

Copolymerization of propylene and ethylene and terpolymerization of propylene, ethylene, and 1‐butene were carried out to compare the characteristics of diether‐ and phthalate‐based Ziegler‐Natta catalysts in a reaction system of pilot scale. The ethylene incorporation with the diether‐based catalyst was higher but the 1‐butene incorporation was lower compared with those of the phthalate‐based catalyst. In the case of copolymers from the diether‐based catalyst, melting behavior, determined through differential scanning calorimetry (DSC), showed a distinct shoulder peak and lots of nuclei were formed during crystallization. The diether‐based catalyst led to polymers having blockier ethylene sequences compared with those of the phthalate‐based catalyst; the highly crystallizable fraction (HIS) containing blockier ethylene sequences was produced with the diether‐based catalyst. These results seem to be the result of regio‐irregular characteristics of the diether‐based catalyst. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 130: 851‐859, 2013

Investigation of the effect of hydrolysis products of postconsumer polyethylene terephthalate bottles on the properties of alkyd resins

AbstractHydrolysis of waste polyethylene terephthalate (PET) flakes obtained from grinding postconsumer bottles was carried out at 200–230°C and molar ratios of PET/H2O were taken as 1/5; 1/10; 1/20. The reaction products, when extracted with boiling water, yielded a water soluble crystallizable fraction (WSCF) and a water insoluble fraction (WIF). These fractions were characterized by acid and hydroxyl value determinations and DSC analysis. WSCF and WIF were used for preparation of alkyd resins. Five long oil alkyd resins were prepared from phthalic anhydride (PA) (reference alkyd resin) or hydrolysis products of the waste PET (PET‐based alkyd resin), pentaerithrithol (PE), soybean oil fatty acid (SOFA), and ethylene glycol (EG). Film properties and thermal degradation stabilities of these alkyd resins were investigated. Drying time, hardness, alkaline resistance, and thermal oxidative degradation resistance of the PET‐based alkyd resins are better than these properties of reference resin. The results show that hydrolysis products of waste PET obtained from postconsumer bottles are suitable for manufacturing of alkyd resins. POLYM. ENG. SCI., 2013. © 2012 Society of Plastics Engineers

Zinc and tin xanthates in the coordination polymerization of propylene oxide

AbstractThe polymerization of propylene oxide with zinc and tin xanthates was studied. Polymerization with both systems was found to be a zeroth‐order, nonterminating process, where the molecular weight was controlled by transfer reactions. It is discussed that these observations were consistent with a mechanism in which the rate‐determining step was the addition of monomer on the growing chain rather than the coordination of the monomer to active sites. These catalysts turned out to be quite stable, even under semiclosed conditions. With zinc isopropyl xanthate, high conversions in short polymerization times could be obtained. The product had a very broad molecular weight distribution and could be split into crystallizable and amorphous fractions. The crystallizable fractions consisted of stereoregular segments separated from each other by stereoirregularities or regioirregularities. The degrees of polymerization of stereoregular segments (S1's) were estimated from melting point measurements. It was found that the melting points and, hence, average S1 values changed in different fractions. It was concluded that there was only one type of active center; however, the rates of wrong additions (e.g., head‐to‐head addition) of incoming monomer controlled the average S1 value of the chain. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011

Middle-Down Fragmentation for the Identification and Quantitation of Site-Specific Methionine Oxidation in an IgG1 Molecule

A middle-down LC/MS approach, for the rapid quantitation and characterization of site-specific methionine oxidation in a recombinant monoclonal IgG1 molecule, is described. An IgG1 antibody was digested with endoprotease LysC under limited proteolytic conditions to produce two major components; an antigen binding fragment (Fab) and a crystallizable fraction (Fc). These fractions were then reduced to produce three major species; light chain (LC), Fc/2 which is the C terminal region of the heavy chain (HC) and the N-terminal heavy chain region (Fd). These three fragments were separated by reversed-phase HPLC using a diphenyl column. The diphenyl column resolved site-specific methionine oxidation in all three subunits. Middle-down N-terminal sequencing with a LCT premier mass spectrometer was used to identify the sites of oxidation in the LC. Sites of oxidation in the Fc/2 were identified using middle-down collision-induced dissociation (CID) on a Qtof premier. This method allowed for the rapid quantitation and identification of oxidation on each methionine residue in an IgG1 molecule.

Alkyd resins based on waste PET for water-reducible coating applications

Simultaneous glycolysis and neutral hydrolysis of waste PET flakes obtained from grinding post-consumer bottles was carried out in the presence of xylene and an emulsifier at 170 °C. The product was separated from ethylene glycol (EG), water, and xylene by filtration, and was extracted by water at boiling point thrice. The remaining solid was named water insoluble fraction (WIF). The filtrate was cooled to 4 °C, and the crystallized solid obtained by filtration was named water soluble crystallizable fraction (WSCF). These fractions were characterized by acid value (AV) and hydroxyl value (HV) determinations. WSCF and WIF were used for preparation of the water-reducible alkyd resins. Three long oil alkyd resins were prepared from phthalic anhydride (PA; reference alkyd resin) or depolymerization product of the waste PET (PET-based alkyd resin), glycerin (G), fatty acids (FA), and glycol (EG; reference alkyd resin) or depolymerization product of the waste PET (PET-based alkyd resin). Film properties and thermal degradation stabilities of these alkyd resins were investigated. Physical properties (drying times and hardness) and thermal degradation stabilities of the PET-based alkyd resin is better than these properties of the reference alkyd resin.

Alkyd resins synthesized from postconsumer PET bottles

Simultaneous glycolysis and neutral hydrolysis of waste PET flakes obtained from grinding postconsumer bottles was carried out in the presence of xylene and an emulsifier at 180 °C. The product was separated from EG, water and xylene by filtration and was extracted by water at boiling point three times. The remaining solid was named water insoluble fraction (WIF). The filtrate was cooled to 4 °C and the crystallized solid obtained by filtration was named water-soluble crystallizable fraction (WSCF). These fractions were characterized by acid value (AV), hydroxyl value (HV) determinations. WSCF and WIF were used for preparation of the alkyd resins. Three long oil alkyd resins were prepared from phthalic anhydride (PA) (reference alkyd resin) or depolymerization product of the waste PET (PET-based alkyd resin), glycerin (G), sunflower oil fatty acids (SOFA) and glycol (EG) (reference alkyd resin) or depolymerization product of the waste PET (PET-based alkyd resin). Film properties and thermal degradation stabilities of these alkyd resins were investigated. Physical properties (drying times, hardness and abrasion resistance) and thermal degradation stabilities of the PET-based alkyd resins are better than these properties of the reference alkyd resin.

Morphological investigation on melt crystallized polylactide homo‐ and stereocopolymers by enzymatic degradation with proteinase K

AbstractPolylactide (PLA) homo‐ and stereocopolymers containing 100, 98, 96, 94, and 92% L‐lactyl units, respectively, were synthesized by ring opening polymerization of L‐lactide and DL‐Lactide, using zinc lactate as catalyst. Differential scanning calorimetric analysis measurements show that incorporation of D‐lactyl units leads to decrease of the crystallization rate of the copolymers. However, the crystallization mechanism and the amount of crystallizable fraction are not affected. The enzymatic degradation was performed at 37 °C in a pH 8.6 Tris buffer containing proteinase K. Two distinct morphologies were obtained by melt crystallization for PLA films with ca. 80 μm of thickness. It is confirmed that proteinase K can degrade both the free and confined amorphous regions. Lamella stacks in spherulites retain their orientation during enzymatic degradation. PLA crystal morphologies are affected by the content of D‐lactyl units. Factors such as the nucleus location and the D‐lactyl units' exclusion as amorphous fraction were considered to elucidate the observed PLA spherulite morphologies. Infrared spectroscopy and mass loss measurements were also combined to better understand the degradation behaviors. © 2008 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 46: 959–970, 2008