Isothermal Crystallization Rate Research Articles

Origin and Nucleation Kinetics of Transcrystalline Layer in Bamboo fiber@nano‐TiO2/Polypropylene Composite

AbstractHerein origin and nucleation kinetics of transcrystalline layer (TCL) in bamboo fiber deposited with nano‐TiO2 (BF@TiO2)/polypropylene (PP) composite is studied. Firstly, the surface morphology, roughness, and energy, as well as crystalline structure (e. g., crystal face indices (hkl)) of BF@TiO2 are analyzed to clarify the origin of TCL in the composite. Subsequently, the nucleation kinetics of TCL in BF@TiO2/PP composite at different crystallization temperatures (Tc) are investigated through polarized optical microscopy. The results find that the surface roughness and energy of BF@TiO2 increase by 47.55 % and 2.41 % compared with untreated BF, respectively. Interestingly, the mismatch rates (MRs) of hkl(BF) vs. hkl(PP) are >320 %. In comparison, the MRs of (101)(BF@TiO2)TiO2 vs. (hkl)(PP) are dramatically decreased to <25 %, suggesting a similar crystal plane between BF@TiO2 and PP matrix. These results indicate that the TCL formation in the composite is more facile in BF@TiO2 than in the untreated BF. During isothermal crystallization, the nucleation and spherulite growth rates decrease as the Tc increases. The interface free energy difference (▵σ) between BF@TiO2 and PP is calculated based on the heterogeneous nucleation theory. The ▵σ is 1.54±0.11 J cm−2, highlighting that the BF@TiO2 strongly induces the PP nucleation.

Highly crystalline, heat resistant and biodegradable copolyesters from fully bio-based bis(pyrrolidone) monomer

Improving the heat resistance of bio-based and biodegradable polyesters is of great significance to extend their applications. Herein, N,N’-trans-1,4-cyclohexane-bis(pyrrolidone-4-methyl carboxylate) (T-CBPMC) was prepared through efficient Michael-addition reaction between dimethyl itaconate and trans-1,4-cyclohexanediamine. The obtained T-CBPMC was copolymerized into aliphatic poly(butylene succinate) (PBS), and a series of PBSPs copolymers with T-CBPMC (BP) molar percentages between 41−80 mol % and weight average molecular weight (Mw) values ranging between 5.77*104 and 6.67*104 g/mol were prepared. BP units efficiently facilitated the melting temperature (203-251 °C) and isothermal-crystallization rate (t1/2 < 20 s) of PBSPs, endowing the highest heat resistance among commercial biodegradable polyesters, which helps maintain stable in pasteurization, high-temperature disinfection, and microwave environments. Moreover, these copolymers displayed remarkable mechanical, gas barrier properties and degradability. PBSP40-PBSP60 obtained high elastic modulus (335–872 MPa) and tensile strength (24.7–31.5 MPa), and good toughness simultaneously. Multiple-ring structures and large steric hindrance of BP units resulted in superior O2 barrier performance than that of non-degradable PET films. Importantly, the PBSP copolyesters showed obvious degradation in water environments and relatively better enzymatic degradation. It was interesting to find that even with 70 % of the BP units, the PBSP copolyesters still retained hydrolysis ability. The resulting PBSP copolyesters open the way for alternative candidates of biodegradable packaging materials with rapid crystallization, high heat-resistance and gas barrier.

Effect of CH2 run length on the crystallization kinetics of sustainable long-spaced aliphatic polyesters

We have studied the isothermal overall crystallization rates and linear growth rates of four symmetric long-spaced aliphatic polyesters (LSAPEs) with 12, 18, 32, or 48 carbons in both the diol and the diacid monomers. With increasing crystallization temperature (Tc) these LSAPEs display discrete rate minima in a number and depth that depend on the length of the methylene spacer between esters. Two rate minima are observed for PE-48,48 and for PE-32,32; one for PE-18,18 and none for PE-12,12. The rate minima are not associated with a change in the mechanism of nucleation and growth or with a change in crystal packing, but occur at Tc where the crystal thickness transitions from a non-integer to a quantized integer number of monomer units. We explain such rate minima based on the self-poisoning feature used earlier to explain similar findings in n-alkanes and other types of precision polyethylene-like systems. In LSAPEs, metastable non-integer crystals attach to the growth front of stable integer crystals retarding their growth until the non-integer segments thicken to complete the layer. Lack of rate minima in the shortest-spaced symmetric polyester is explained by a small difference in lamellar thickness between non-integer and integer layered crystals which favors the formation of integer crystals at any Tc.

Isothermal crystallization process and thermal analysis of polylactic acid/cotton fiber composites during thermal degradation

ABSTRACT The effects of reactive and non-reactive surface treatment agents on the isothermal crystallization rate and subsequent melting behavior of polylactic acid/cotton fiber (PLA/COF) composites before and after accelerated degradation testing at 60°C for 2000 h were demonstrated. The results showed that the crystallization rate of PLA was rapidly accelerated by the incorporated COF, while the use of epoxy-based reactive surface treatment agents inhibited the movement of PLA molecular chains and reduced the crystallization rate and melting point of the PLA/COF. These results suggest that the reactivity of the agent affects the crystallization behavior of the composite during long-term use.

Crystallization and melting kinetics of low tacticity polypropylene in relation to preformed nuclei and uncrystallizable defects

Fast scanning calorimetric experiments were carried out on low-isotacticity polypropylene (LT-PP) to evaluate the effect of pre-nucleation below the glass transition temperature (also known as Tammann's crystal nuclei development method) on the kinetics of crystallization and melting. The melting kinetics of secondary crystallized LT-PP was not affected by the presence of crystal nuclei, although the isothermal crystallization rate of LT-PP was accelerated by increasing the amount of crystal nuclei. The maximum primary crystallization decreased with increasing amounts of crystal nuclei. This behavior can be explained by the formation of uncrystallizable defects between the crystalline domains.

Effect of Two Crystalline Forms on the Multiple Melting and Crystallization Kinetics of Thermoplastic Polyurethane

Exploring the origin of multiple melting of thermoplastic polyurethane (TPU) is of great significance for comprehending the mechanism for its phase transition. Herein, the effects of two crystal forms (Form-I and Form-II) and crystal form transition on the melting behaviors and crystallization kinetics of TPU are reported. As the function of the crystallization temperature (Tc), Form-II and Form-I develop at Tc ≥ 130 °C and Tc ≤ 130 °C, respectively, which leads to distinct differential scanning calorimetry (DSC) melting curves of TPU. It is found that the repeated melting–recrystallization occurs during the melting of Form-I, which includes the crystal form transition of Form-I to Form-II, resulting in four melting peaks in the DSC heating curves of Form-I. The results reveal that the mesophase (Form-I) could transform into the stable crystal form (Form-II) through melting–recrystallization upon heating in TPU, and TPU has the ability to continuously reorganize the ordered structure upon heating. Meanwhile, the intervention of Form-I significantly increases the overall isothermal crystallization rates, and the motion ability of TPU molecular chains is the crucial factor affecting the generation of Form-I.

Enhanced crystallization of poly(lactic acid) bioplastics by a green and facile approach using liquid poly(ethylene glycol)

AbstractPolylactic acid (PLA) bioplastics have attracted increasing attention from both academic and industrial researchers due to their biomass‐derived nature and low toxicity for the human body and environment. A major drawback of PLA is slow crystallization during processing, which considerably limits its commercial applications. In this study, a simple and low‐cost approach involving the addition of eco‐friendly low molecular weight poly(ethylene glycol) (PEG; 400 g/mole) as a green solvent was developed to enhance the PLA crystallization process. Differential scanning calorimetry and polarized optical microscopy data revealed that the introduction of PEG into PLA considerably increased the PLA crystallization rate. In particular, the isothermal crystallization rate of a system with a PLA/PEG mass ratio of 70/30 was more than seven times greater than that of neat PLA. In addition, the miscibility, thermal properties, and microstructures of various PLA/PEG blends were determined. A substantial reduction in the equilibrium melting temperature of PLA after PEG addition confirmed that these polymer blends were thermodynamically miscible in the melt, which strongly influenced the PLA crystallization rate. Furthermore, the addition of PEG increased the regularity of PLA crystals and induced the formation of ring‐banded PLA spherulites with periodic twisted lamellae.

Physical properties of oleogels fabricated by the combination of diacylglycerols and monoacylglycerols

AbstractOleogelation is an efficient way to offer healthy substitutes for trans and saturated fatty acids in processed foods. Multicomponent gels are of particular interest due to the ability to tune gel properties by altering the component proportions. In this study, monoacylglycerol (MAG) and diacylglycerol (DAG) are used as gelator blends and the influence of the gelator ratio on the characteristics of oleogels was investigated. The crystallization and melting behavior, solid fat content (SFC), crystal morphology, polymorphism and mechanical properties of the oleogels were characterized. The oleogels with higher gelator level displayed increased oil binding ability and shorter crystal formation time. The oleogels with higher MAG ratio exhibited more fibrillar‐like crystals, and the mixed oleogels with MAG:DAG of 5:5 showed altered crystal morphology with finer crystal size, reduced crystallization enthalpies and solid state possibly due to the increased nucleation seeds promoted by MAG. The oleogels with high MAG level showed lower equilibrium SFC during isothermal crystallization but faster crystallization rate, higher hardness and elasticity. Therefore, by changing the ratio of DAG to MAG, the crystallization profile and rheological properties of oleogels can be tailored. The oleogels can be used as traditional solid fat substitutes to reduce saturated fatty acid content in lipid‐based products.

Effect of carrier material on the thermodynamic properties and recrystallization kinetics of andrographolide-solid dispersion

This work investigated the effect of the lipophilic long carbon chain of carrier material on the thermodynamic properties and the recrystallization kinetics of solid dispersion (SD). The thermodynamic properties and recrystallization kinetic parameters of amorphous andrographolide (AG)-PEG8000 laurate (SM12)-SD, AG-PEG8000 palmitate (SM16)-SD and AG-PEG8000 behenate (SM22)-SD were determined and calculated by differential scanning calorimetry combining AGV equation and Avrami equation. From AG-SM12-SD to AG-SM22-SD with the increase of the carbon chain length of carrier material, the glass transition temperature, the maximum relaxation enthalpy and the mean relaxation time of SD increased at first and then decreased; the isothermal crystallization rate constants at different temperatures and non-isothermal crystallization rate constants at different heating rates of SD showed a trend of decreasing at first and then increasing. Increasing the carbon chain length of polyethylene glycol fatty acid ester can improve the space-limiting effect of the carrier material on the AG molecule, but the carbon chain length of carrier was not the longer the better. SM16 had the appropriate spatial scale, which better limited the molecular mobility of AG in SD, so AG-SM16-SD has better thermodynamic stability and recrystallization kinetic stability.

Singling Out the Role of Molecular Weight in the Crystallization Kinetics of Polyester/Clay Bionanocomposites Obtained by In Situ Step Growth Polycondensation

The isothermal crystallization kinetics of a set of bio-nanocomposites produced by in situ catalytic step growth polycondensation of adipic acid and 1,4-butanediol in the presence of Moroccan clay beidellite (BDT) organo-modified with hexadecyltrimethylammonium bromide (cetyltrimethylammonium bromide, CTA) was investigated and compared with that of the parent poly(butylene adipate) (PBA) matrices from which the clay had been extracted. In situ bio-nanocomposites had different contents (0–5 wt %) of CTA/BDT nanofillers characterized by different extents of organo-modification (CTA/BDT equivalent ratios from 0 to 5). The isothermal crystallization rates of the bio-nanocomposites and of the parent PBA matrices were investigated by differential scanning calorimetry (DSC) at 45, 40, and 37 °C and analyzed according to the Avrami model. The bionanocomposites with an intermediate (2 wt %) concentration of organoclays with a higher CTA/BDT ratio (3 and 5) showed the highest exfoliation degree, along with an increase in the crystallization rates, compared to those of the parent PBA matrices, which was larger than that in the other nanocomposites. The lack of a simple correlation between the nanoclay content/composition and crystallization kinetics was ascribed to the molecular mass, an additional variable for in situ bio-nanocomposites as compared to nanocomposites prepared by simple physical blending of nanoclays with a single polymer matrix. The specific contribution of the molecular mass to the crystallization kinetics was untangled from those of the organoclay content and CTA/BDT ratio by comparing each bio-nanocomposite with its parent polymer matrix. The crystallization rate of the nanocomposites was always found to reach a maximum within an intermediate range of molecular weights of the polymer matrix, a behavior previously reported only for pure polymers. Such differences in the crystallization rate of in situ bio-nanocomposites may affect the crystalline phase morphology and, in polymorphs such as in PBA, phase composition, with consequent effects on properties that may be of interest for specific applications.

Enhancing the crystallization of biodegradable poly(ε-caprolactone) using a polyvinyl alcohol fiber favoring nucleation

In this study, biodegradable poly(ε-caprolactone) (PCL)/polyvinyl alcohol (PVA) fiber composites were prepared using melt processing techniques with different PVA fiber contents. The effect of PVA fiber on the non-isothermal and isothermal melt crystallization kinetics of PCL/PVA fiber composites was studied by using differential scanning calorimetry. Non-isothermal crystallization peak temperatures were enhanced significantly, as exemplified by about 20 K increase for the composite loaded with 5 wt% PVA fiber at a cooling rate of 20 K/min compared to that of neat PCL. The crystallization half-time decreased from 1.67 min for neat PCL to 0.80 min for composite with 5 wt% PVA fiber at a cooling rate of 5 K/min. PVA fiber was also found to dramatically accelerate the isothermal crystallization rate of PCL/PVA fiber composites. The crystallization half-time of composite containing 5 wt% PVA fiber was reduced by more than 10 times compared with neat PCL. Moreover, dynamic mechanical analysis results showed that PVA fiber had a strengthening effect on the PCL.

Exceptional cold-crystallization kinetics of erythritol-polyelectrolyte enables long-term thermal energy storage

Long-term thermal energy storage balances the seasonal variations in renewable energy supply and demand, but applied storage concepts require improved performance in efficiency, reliability and capacity. In principle, supercooling and cold-crystallization offer a way to store heat for an extensive amount of time. In this approach, crystallization behaviour of the material governs the storage performance, as it directly relates to optimal efficiency, length of the storage period and heat release properties. This work explains the unique cold-crystallization behaviour of erythritol in cross-linked sodium polyacrylate. To this end, isothermal cold-crystallization was measured experimentally and analysed with the Avrami equation. Although the cold-crystallization rate constant follows the Arrhenius equation, it drastically decreases near the glass transition region and diverges from the equation. Thermal history also influences the cold-crystallization behaviour. Increases in cooling end-temperature reduce the subsequent crystallization time and promote metastable polymorph formation. These findings stem from the peculiar energy landscape of erythritol in cross-linked sodium polyacrylate. The landscape is classified as kinetically strong and thermodynamically fragile, which facilitates long-term thermal energy storage. Consistent supercooling and cold-crystallization behaviour of the material enables predicting the time-dependent crystallization rate at different temperatures. This confirms applicability of the two-stage Arrhenius-VFT model for temperature dependence and supports storage design in real-life applications. • Cold-crystallizing PCM for long-term TES with 230–350 MJ/m 3 storage capacity. • Spherical cold-crystallization enables modelling and predicting the kinetics. • Cold-crystallization follows Avrami equation and combined Arrhenius-VFT dependency. • Crystallization rate decreases drastically when approaching glass transition region. • Reducing cooling temperature increases following isothermal crystallization rate.

The overall crystallization behavior of polyethylene/wax blends as phase change materials for thermal energy storage: A mini review

AbstractThis review paper deals with the overall crystallization behavior of polyethylene/wax blends as phase change materials (PCMs) for thermal energy storage with the determination of their thermal properties. The addition of molten wax to the polyethylenes decreases the crystallization and melting temperatures of the blends. However, incorporating fillers to the polyethylene/wax blends can either decrease or increase the crystallization and melting temperatures of the composites depending on the filler type. The normalized enthalpy values of linear low‐density polyethylene showed no significant change when increasing the wax content. On the contrary, the normalized enthalpy values of the wax in the blends were lesser than that of pure wax and increased with increasing wax content. Since the wax in the blend had a lower crystallinity compared to pure wax, this influences its effectiveness as a PCM for thermal energy storage. The effect of different polyethylenes on the wax morphology gave rise to enhance phase separation when wax was blended to high‐density polyethylene as compared to the other polyethylenes. On the contrary, the effect of various waxes on the morphology of polyethylene resulted in different morphologies due to the molecular weight of the wax used and the structure of the polyethylene chain. The addition of fillers to the polyethylene (PE)/wax samples resulted in enhanced phase separation. The overall isothermal crystallization rate and the equilibrium melting temperature of PEs in the PEs/wax blends were depressed by wax addition due to the wax dilution effect.

Miscibility, crystallization and mechanical properties of poly[(3‐hydroxybutyrate)‐co‐(4‐hydroxyvalerate)]/poly(propylene carbonate)/poly(vinyl acetate) ternary blends

AbstractA ternary blend of poly[(3‐hydroxybutyrate)‐co‐(4‐hydroxyvalerate)] (P34HB), poly(propylene carbonate) (PPC) and poly(vinyl acetate) (PVAc) was initially melt‐blended in an effort to obtain an excellent balance of mechanical performance. The effect of PVAc content on the miscibility, phase morphology, thermal behavior, isothermal melt crystallization and mechanical properties of P34HB/PPC/PVAc ternary blends was systematically investigated. Dynamic mechanical analysis indicated that P34HB and PPC were immiscible, and PVAc exhibited immiscibility with PPC. PVAc was selectively dispersed in the P34HB matrix and phase morphology was refined by reducing the interfacial tension. Moreover, the PVAc component suppressed the cold crystallization and reduced the isothermal melt crystallization rate of P34HB in the ternary blends. Unexpectedly, marked increases of 32.7% and 3025% were achieved in the tensile modulus and elongation of the ternary blend containing 20 wt% PVAc compared to neat P34HB. Meanwhile, the strength did not deteriorate. The unusual combination of high ductility, strength and modulus is of great potential for expanding the practical application of sustainable and biological polymers. © 2021 Society of Industrial Chemistry.

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 behavior of polylactide nucleated by octamethylenedicarboxylic di(2-hydroxybenzohydrazide): Solubility influence

The crystallization ability of polylactide (PLA) was improved by the addition of a hydrazide compound, octamethylenedicarboxylic di(2-hydroxybenzohydrazide) (OMBH). The nucleation efficiency of OMBH significantly depended on its solubility during annealing treatment. The solubility of OMBH increased gradually with increasing the final annealing temperature (Tf) and/or decreasing the addition concentration of OMBH (COMBH). At a certain COMBH (e.g. 0.5 wt%), the crystallization of OMBH shifted to a lower temperature with increasing Tf due to the increased OMBH solubility. This decreased the crystallization temperature, crystallization enthalpy, and isothermal crystallization rate of PLA. Additionally, at a certain Tf (e.g. 200 °C), the crystallization temperature and nucleation efficiency of OMBH increased with its concentration, resulting in the increase of crystallization temperature, crystallization enthalpy, and isothermal crystallization rate of PLA.

Nucleation and Crystallization of PA6 Composites Prepared by T-RTM: Effects of Carbon and Glass Fiber Loading.

Thermoplastic resin transfer molding (T-RTM) is attracting much attention due to the need for recyclable alternatives to thermoset materials. In this work, we have prepared polyamide-6 (PA6) and PA6/fiber composites by T-RTM of caprolactam. Glass and carbon fibers were employed in a fixed amount of 60 and 47 wt.%, respectively. Neat PA6 and PA6 matrices (of PA6-GF and PA6-CF) of approximately 200 kg/mol were obtained with conversion ratios exceeding 95%. Both carbon fibers (CF) and glass fibers (GF) were able to nucleate PA6, with efficiencies of 44% and 26%, respectively. The α crystal polymorph of PA6 was present in all samples. The lamellar spacing, lamellar thickness and crystallinity degree did not show significant variations in the samples with or without fibers as result of the slow cooling process applied during T-RTM. The overall isothermal crystallization rate decreased in the order: PA6-CF > PA6-GF > neat PA6, as a consequence of the different nucleation efficiencies. The overall crystallization kinetics data were successfully described by the Avrami equation. The lamellar stack morphology observed by atomic force microscopy (AFM) is consistent with 2D superstructural aggregates (n = 2) for all samples. Finally, the reinforcement effect of fibers was larger than one order of magnitude in the values of elastic modulus and tensile strength.

Enhancement of the properties of biosourced poly(3-hydroxybutyrate-co-4-hydroxybutyrate) by the incorporation of natural orotic acid

The aim of this study is to use natural orotic acid (OA) as a sustainable, environmentally friendly additive to improve the crystallization, rheological, thermal, mechanical, and biodegradation properties of bacterially synthesized poly(3-hydroxybutyrate-co-4-hydroxybutyrate) (P34HB). OA was found to be an efficient nucleating agent for P34HB, and dramatically enhanced both non-isothermal and isothermal crystallization rates. The incorporation of OA increased nucleation density and decreased spherulite size, but had little effect on the crystalline structure. The rheological properties of the P34HB were greatly improved by the solid filler OA, particularly when a percolation network structure was formed in the blends. The thermal stability of P34HB was strongly enhanced, as exemplified by the ~23 °C increase in the onset thermal decomposition temperature (To) for the blend loaded with 5 wt% OA compared to that of pure P34HB. Moreover, the yield strength and elongation at break of P34HB containing 0.5 wt% OA increased by 25% and 119%, respectively. The most intriguing result was the clear enhancement in the enzymatic hydrolysis rates of the P34HB/OA blends compared to that of neat P34HB. The synergetic improvement in these properties may be of significant importance for the wider practical application of biosourced P34HB.

Morphology and Isothermal Crystallization Kinetics of Polypropylene/Poly(ethylene-co-vinyl alcohol) Blends

Abstract Polypropylene (PP)/poly(ethylene-co-vinyl alcohol) (EVOH) blends were prepared by melt blending using PP-g-MAH as a compatabilizer. The microstructure and rheological behavior of PP/EVOH blends were studied. The results showed the that EVOH particles were uniformly dispersed in the PP matrix and inhibited the mobility of PP chains. The isothermal crystallization kinetics and morphology development of PP/EVOH blends were compared with that of pure PP. It was found that the EVOH essentially acted as an effective nucleating agent for PP, which could significantly increase the nucleation rate because the EVOH molecules in PP/EVOH blends aggregated together to form interface. Therefore, the introduction of EVOH increased the overall rate of isothermal crystallization compared with pure PP, although the PP molecular chains would be hindered seriously if excessive amounts of EVOH were added. X-ray diffraction showed that pure PP and PP/EVOH blends exhibited an identical crystal structure, and the crystallinity of the PP phase in the blends was not significantly different from that of pure PP.