Melting Of Crystallites Research Articles

Ultra‐high molecular weight polyethylene micro‐ribbon fibers gel spun using orange terpenes

AbstractToxic, hazardous petrochemical solvents are commonly used for industrial‐scale ultra‐high molecular weight polyethylene (UHMWPE) fiber production, but orange terpenes, a byproduct of orange fruit production, present a bio‐derived, sustainable alternative. In this work, fine UHMWPE fibers were spun using orange terpenes as the spin solvent, hot‐drawn at a draw ratio of 5:1, investigated for their morphology, microstructure, and thermal and mechanical properties. The resulting fibers exhibited a flat, micro‐ribbon cross‐section, which is highly desirable for achieving high fiber volume fractions in UHMWPE‐fiber reinforced composites. After drawing, the fibers possessed 4× greater breaking tenacity than any previously published studies on UHMWPE fibers spun using orange terpenes with a tenacity of 8.6 cN/dtex and tensile modulus of 229.2 cN/dtex. Microstructural analysis via differential scanning calorimetry and X‐ray diffraction revealed that the hot drawing process significantly increased molecular orientation, but crystallinity decreased due to crystallite melting during drawing. Therefore, the mechanical properties of these fibers may be significantly improved with optimization of the fiber drawing process. This work establishes the strong potential of orange terpenes as an environmentally‐friendly alternative solvent for UHMWPE gel spinning and sets a foundation for future parametric optimization of the spinning and drawing of these fibers.Highlights Micro‐ribbon ultra‐high molecular weight polyethylene fibers were prepared using bio‐solvent orange terpenes. Flat profile enables tight packing, aspect ratio maintained after drawing. Drawn fibers were 4× stronger than any previous work with orange terpenes. Near‐melt drawing reduced crystallinity, improved molecular alignment.

Syndiotactic Poly(Substituted Methylene)s with Alkyloxycarbonyl Side Chains: Effects of Side Chain Chirality on the Main Chain Helix and Crystallinity

AbstractSyndiotactic poly(substituted methylene)s (st‐PMs) with alkyloxycarbonyl side chains form hexagonal columnar liquid crystals (Colh LCs), wherein the main chain adopting either right‐ or left‐handed helices is arranged in a 2D hexagonal lattice. This study investigates the main chain conformation for st‐PMs with chiral side chains, designated as st‐P8(3,7Me)‐fSS. st‐P8(3,7Me)‐fSS polymers possess 3,7‐dimethyloctyloxycarbonyl side chains at different S‐enantiomeric fractions, fS. In chiral st‐P8(3,7Me)‐fSS with an fS > 50%, the main chain adopts a one‐handed helical conformation along the longer contour with increasing fS. The fS influences the crystallinity of the polymers. Chiral P8(3,7Me)‐fSS polymers crystallize the Colh LCs upon cooling. The crystallite size, melting temperature, and fusion enthalpy increase with fS. Racemic st‐P8(3,7Me)‐50S does not crystallize.

Composition controllable multifunctionality of PVDF/PMMA/BaTiO3/OMMT based ternary and quaternary hybrid polymer nanocomposites

State-of-the-art engineered multifunctional nanocomposites composed of different polymer matrices and functional nanomaterials are in high industrial demand for advances in all-solid-state flexible device technologies. Within this framework, the host matrices of poly(vinylidene fluoride) (PVDF) and its blend with poly(methyl methacrylate) (PMMA), and the barium titanate (BaTiO3) and organo-modified montmorillonite (OMMT) clay mixed nanomaterial dispersed ternary PVDF/x wt% (BaTiO3+OMMT) and quaternary (PVDF+PMMA)/x wt% (BaTiO3+OMMT) hybrid polymer nanocomposites (HPNCs) are prepared through ultrasonicated homogenized solution casting method. The XRD patterns and FTIR transmittance spectra confirmed the composition dependent crystal phases of the PVDF and the heterogeneous polymer-polymer and polymer-nanomaterial interactions in these HPNC materials. The DSC measurements explained a huge alteration in the PVDF crystallite melting temperatures and also the degree of crystallinity of different HPNC materials. The UV–Vis absorbance of these hybrid materials depends strongly on their composition design and demonstrated dual energy band gaps attributed to host polymer matrices and the nanofillers. The dielectric permittivity dispersion in the broadband frequency range of 20 Hz − 1 GHz explains the contribution of several polarizations and relaxation processes in these complex composites, at 27 °C. Appreciably high dielectric permittivity (4 to 7) in the 20 Hz − 1 MHz range and low permittivity at the ultra high radio frequencies confirmed the promising nanodielectric characteristics of these hybrid materials. The interesting structure-property relationship, tunable energy band gaps, a wide range of composition controllable dielectric permittivity, and frequency dependent electrical conductivity revealed the usefulness of these HPNCs in making flexible-type innovative optoelectronic, capacitive energy storage, and microelectronic devices.

Stretching-Induced Melting and Recrystallization Polymorphism Revealed in Polybutene-1

The crystalline structures of polymorphic polymer not only are determined by the processing parameters but also could further evolve within the service period. In this work combining in-situ wide-angle X-ray diffraction and ex-situ differential scanning calorimetry, the stretching-induced crystallite evolution was studied for polymorphic polybutene-1 (PB) within a broad stretching temperature (Tstretching) range of 30–115 °C. First of all, it was found that although the initial crystallites were in the most thermodynamically stable modification of the trigonal phase, the metastable but kinetically favored tetragonal phase was generated during stretching at the elevated temperatures because of crystallite melting and subsequent recrystallization. What is more interesting is that those stretching-generated amorphous fractions also have the possibility of recrystallizing into the trigonal form I′ when cooled to room temperature, depending on Tstretching. These results demonstrate that the polymorphism selection occurs in the stretching-induced recrystallization, where form II might be generated during stretching at the elevated temperature and form I′ is obtained by cooling. The unusual re-appearance of the trigonal form I′ may be associated with the local confinement crystallization caused by the residual crystallites. The combination of structural evolution with mechanical response disclosed that the stretching-induced recrystallization requires macroscopic yielding to destroy the crystallite skeleton for melting. Furthermore, the increase of lamellar thickness decreases the amount of stretching-induced amorphous phase and increases the critical Tstretching of recrystallization into forms II and I′. Based on the quantitative results, a threshold criterion of stretching-melted PB, which is crystallinity of around 12.6%, was identified to be required for recrystallization of the trigonal phase form I′ by cooling the stretched form I crystallites.

Calorimetric Study of Mixtures of Polypropylene with 90 wt % Low-Molecular Organic Compounds after Plastic Deformation at a High Pressure

Mixtures of polypropylene (10 wt %) with anthracene, phthalocyanine, indigo, adamantane, congo red, spiropyran, safranin, methyl orange, bromocresol purple, phenolphthalein, fluorescein, phenol red, thymol blue, aspartic acid, cyanuric acid, thymolphthalein, and rhodamine were subjected to plastic deformation at a pressure of 1 GPa on an anvil-type high-pressure apparatus. It was found by DSC that the thermograms of heating of the deformed mixtures in the temperature range below Tm of the polymer contain endothermic peaks of melting of small polymer crystallites with enthalpies reaching 220–240 J/g in some samples, as well as exothermic peaks of cold crystallization with enthalpies reaching 430–470 J/g. The melting was described by bi- and trimodal peaks, whose total enthalpy reached 2200–2400 J/g in some mixtures. The polymer crystallization in the deformed mixtures was described by single exothermic peaks, whose enthalpies differed little from the crystallization enthalpy of the starting polypropylene. An increase in the enthalpies of thermal processes in the deformed mixtures was attributed to the appearance of double electric layers at interfaces between the mixed phases.

Stress‐free two‐way shape memory property and microstructure evolution of single‐phase polymer networks

AbstractIn this work, single‐phase polymer networks with excellent stress‐free two‐way shape memory effect (2W‐SME) were successfully fabricated based on poly(ethylene‐co‐vinyl acetate) (EVA) and dicumyl peroxide. The microstructural evolution during actuation was repeatable and reversible, as demonstrated by the in situ wide‐angle X‐ray scattering. During multiple heating and cooling cycles, the (110) and (200) reflections of EVA appeared with increasing intensity, and the orientation degree was high at the low temperature point (10°C), suggesting that the oriented crystallites are present throughout the entire sample and hold extended conformation of the polymer strands in the amorphous phase. When heating to a high temperature (Thigh = 70°C), partial melting of crystallites leads to the contraction of the material, and the intensity of the (110) and (200) reflections and the orientation became smaller, indicating that the residual oriented crystallites could still provide an anisotropic skeleton for the oriented recrystallization of the amorphous molecular chain. Moreover, the reversible actuation strain showed a maximum value of 15.6% at a Thigh of 72°C and was present even at a Thigh of 80°C when the polymer had a very small crystalline fraction (2.2%). Considering the remarkable stress‐free 2W‐SME, EVA may have potential applications in smart grippers, actuators, and sensors.

Melting of crystallites in a solid porous matrix and the application limits of the Gibbs-Thomson equation.

A thermodynamic model is proposed to describe the melting of lamellar crystallite in a solid medium. This model includes a modification of the Gibbs-Thomson equation to make it applicable to the above-mentioned crystallites. The need for such modification is supported experimentally by studying the impact of the surroundings on the melting point of the crystallites. In particular, the application of the model to nanocrystals in open-porous systems makes it possible to determine the analytical relations for the melting point, the heat of melting, and the inverse effective size of the pores. The fitting of the experimental data with these functional relations then allows for the calculation of the nanocrystalline density, pressure in the nanocrystal, and difference in the surface tension coefficients at the nanocrystal-matrix interface and melt-matrix interface, as well as the difference in the surface entropies per unit area at the nanocrystal-matrix and melt-matrix interfaces.

WAXS in-situ study of R-BAPB polyetherimid double-melting behavior

Reactor particles of nascent polyetherimid (PI) R-BAPB powder consist of numerous morphological units of the lamellar type, which have semicrystalline structure. Two endo-peaks at 318 °C and 340 °C were observed in the DSC thermogram of the PI powder. A unique in-situ thermo-WAXS experiment showed no significant difference in X-ray peak profiles when the sample was heated from room temperature up to 330 °C, (the valley between the low- and high-temperature endo-peaks). At that point the WAXS reflections became sharper and much better resolved without a visible crystal cell transformation. It was revealed that the degree of crystallinity dropped near 330 °C and continued decreasing until the complete melting of the sample. The low-temperature endo-peak is associated with melting of numerous small crystallites leading to the sharp amorphization of the sample and to a significant increase in the apparent crystallite size at 330 °C. The high-temperature endo-peak can then be attributed to melting of the larger crystallites formed from the melt during isothermal crystallization at 330 °C. Using WAXS profiles, it was also possible to evaluate the volumetric coefficient of thermal expansion of the crystalline part of the studied polymer as CTEvol = 3.8·10−4 K−1.

An insight into tapioca and wheat starch gelatinization mechanisms using TD-NMR and complementary techniques.

To provide evidence for previously proposed assumptions concerning starch gelatinization sub-mechanisms, a more detailed investigation was carried out using multiscale analysis of a starch type selected for its marked difference. Tapioca starch was chosen due to its cohesive/springy properties and its growing use in the food industry. Time-domain nuclear magnetic resonance (TD-NMR) was used to investigate the leaching of material, water absorption and crystallite melting in hydrated tapioca starch (45%). The interpretation of T2 mass intensity evolutions, especially those of the (intra- and extra-granular) aqueous phases, was discussed drawing on complementary techniques such as microscopy, Rapid Visco Analyser (RVA), differential scanning calorimetry (DSC) and swelling factor (SF) and solubility index (SI) measurements. Results show that the T2 assignments usually proposed in the literature are dependent on starch origin. The differences in T2 evolutions (value and mass intensity) observed between wheat and tapioca starches at intermediate hydration levels could be linked to the different gelatinization behaviour of tapioca starch involving the latter's higher granule rupture level, higher gelatinization temperature and greater swelling power above its gelatinization temperature.

Stereocomplex and individual crystallization behavior of symmetric or enantiomeric substituted Poly(lactic acid)s random copolymers with high crystallizabilities

Stereocomplex (SC) crystallization is reported for the first time for the enantiomeric blends of random copolymers of l-configured poly(l-2-hydroxybutanoic acid-co-l-2-hydroxy-3-methylbutanoic acid) [P(L-2HB-co-L-2H3MB)] (49/51) and d-configured poly(d-2-hydroxybutanoic acid-co-d-2-hydroxy-3-methylbutanoic acid) [P(D-2HB-co-D-2H3MB)] (47/53) with high individual crystallizabilities. Unblended l-configured P(L-2HB-co-L-2H3MB) and d-configured P(D-2HB-co-D-2H3MB) formed individual crystallites through purification, solvent evaporation, and melt crystallization. Three types of individual crystallites (provisionally named as α-, β-, and γ-forms) were observed in the unblended copolymers depending on the crystallization methods. SC crystallites were formed in the blends through solvent evaporation and melt crystallization method. All types of monomer units cocrystallized in the individual and SC crystallites. The melting and equilibrium-melting temperatures of SC crystallites in the blends were 192.5–203.7 °C and 205.2 °C, respectively, which were significantly higher than the melting temperatures of individual crystallites in the unblended copolymers (61.6–133.1 °C). The maximum radial growth rate of SC crystallites (13.5 μm min−1) was 10 and 27 times higher than those of individual crystallites of the unblended copolymers (1.4 and 0.5 μm min−1), indicating that SC crystallization increased the crystallization rate. SC crystallization proceeded via regimes II and III. The copolymer crystallizability, monomer cocrystallizability, and crystallization rate of P(L-2HB-co-L-2H3MB) (49/51) and P(D-2HB-co-D-2H3MB) (47/53) are compared with those reported for the series of symmetric or enantiomeric polymer blends of poly(l-lactic acid-co-l-2-hydroxybutanoic acid) (56/44) and poly(d-lactic acid-co-d-2-hydroxybutanoic acid) (52/48) with lowindividualcrystallizabilities and poly(l-lactic acid-co-l-2-hydroxy-3-methylbutanoic acid) (47/53) and poly(d-lactic acid-co-d-2-hydroxy-3-methylbutanoic acid) (47/53) with noindividualcrystallizability.

In situ synchrotron small angle X-ray scattering investigation of structural formation of polyethylene upon micro-injection molding

A customized micro-injection molding apparatus with a pair of diamond windows in the filling cavity was specifically designed to simulate the extreme processing conditions inherent in the practical micro-molding process. This setup combined with synchrotron radiation allows real-time investigation of multi-scale structural development during the manufacturing process, which enables evaluation of flow-induced crystallization features for a range of polymeric materials. In this study, the structural evolution of high density polyethylene at the nanoscale was investigated by in situ synchrotron small angle X-ray scattering technique under injection molding. The respective structural parameters of kebab lamellae (including the long period, and the average thickness of crystalline lamellae and amorphous phase) and shish formation (such as the radius of gyration, length, and misorientation of the shish) were extensively analyzed from the resulting data. The growth of kebab crystals was found to exhibit a two-step behavior: melting of thin crystallites followed by a recrystallization process occur at the onset of molding whereas an annealing-induced perfectioning of the lamellae is activated at a later stage. In spite of the initial decrease of the shish length and radius, there is an overall increase in the length and misorientation of the shish structure at later times, which can be attributed to a crystallization of partially oriented chains onto the longitudinal surface of the existing shish. The results acquired by the unique combination of this apparatus and synchrotron radiation can provide an effective means to predict the structural formation and modulate the morphology of final products in practical micro-injection molding process of polymers.

In-situ WAXS study of the crystal structure of R-BAPB oligoimide during heating

In the process of this work, an oligoimide FT-BAPB-R-BAPB-FT was synthesized, the particles of which consist of numerous lamellas having a semi-crystalline structure. On the DSC thermogram of oligoimide powder, two endo peaks were observed at 281.1°C and 306.4°C. A unique WAXS experiment was performed in-situ by heating the reactor oligoimid powder in a heat chamber. There was no significant difference in the X-ray profiles when the sample was heated. It should be noted that the transformation of the crystalline cell does not occur until the sample melts. It was revealed that the degree of crystallinity decreases during heating. We believe that the low-temperature endopeak is associated with the melting of small crystallites and amorphization of the sample. However, a significant increase in crystal size was found to be a result of recrystallization. Thus, the high-temperature endopic corresponds to the melting of larger crystallites.

Manipulating the physical states of confined ibuprofen in SBA-15 based drug delivery systems obtained by solid-state loading: Impact of the loading degree.

Using the Milling-Assisted Loading (MAL) solid-state method for loading a poorly water-soluble drug (ibuprofen, IBP) within the SBA-15 matrix has given the opportunity to manipulate the physical state of drugs for optimizing bioavailability. The MAL method makes it easy to control and analyze the influence of the degree of loading on the physical state of IBP inside the SBA-15 matrix with an average pore diameter of 9.4 nm. It was found that the density of IBP molecules in an average pore size has a direct influence on both the glass transition and the mechanism of crystallization. Detailed analyzes of the crystallite distribution and melting by Raman mapping, x-ray diffraction, and differential scanning calorimetry have shown that the crystals are localized in the core of the channel and surrounded by a liquid monolayer. The results of these complementary investigations have been used for determining the relevant parameters (related to the SBA-15 matrix and to the IBP molecule) and the nature of the physical state of the confined matter.

Structural composition and thermal stability of extracted EVA from silicon solar modules waste

Ethylene-vinyl acetate (EVA), a copolymer of ethylene and vinyl acetate, is widely used as an encapsulant in the silicon solar module to bind the different layers together and protecting the solar cells from over stressing, cracking, and environmental effects. In this work, EVA has been recovered successfully from the used silicon solar module by thermal treatment at 170 °C temperature and the application of mechanical force. The established process is completely environment-friendly, as the EVA layer was recovered without any degradation and emission of any gas. The presence of extracted EVA and its chemical composition was confirmed from FTIR and EDAX measurements. It was observed from Thermogravimetry (TGA) and Differential thermogravimetry (DTG) that thermal degradation of EVA was a two-step process, and also the rate of reaction was fast in an air environment as compared to nitrogen environment. The extracted EVA is thermally stable until 215 °C in the air environment. From Differential scanning calorimetry (DSC) analysis, two endothermic peaks were observed at temperature 37 °C and 55 °C, which may be due to beginning of melting of vinyl acetate and ethylene crystallites respectively in air and nitrogen environment. From UV–visible spectroscopy, it was found that above 500 nm, the extracted EVA is transparent. After examined through the various characterization, it has been observed that extracted EVA shows quite similar properties as that of commercially available EVA. Therefore, the recovered EVA may be used in the encapsulation of solar modules and other applications in packaging and textile industries.

Fatigue of carbon cord-rubber composites: Effect of frequency, [formula omitted] ratio and life prediction using constant life models

The influence of frequency and R ratio on tensile fatigue of carbon cord reinforced HNBR composites has been studied. Frequency was found to have negligible effect on fatigue life, due to minimal heat build-up even at the highest frequency. Longer fatigue life at higher R ratios at a given maximum cyclic stress level was associated with the dynamic process of forming and melting of crystallites during loading and unloading, leading to a crack-arresting effect. The applicability of various analytical constant life diagram (CLD) models showed that the modified Harris’s CLD and piecewise linear CLD gave a reasonably good agreement with experimental fatigue data.

Melting of 1-octadecene inside the pores of open-morphology silica gel: thermodynamic model and experimental studies

Melting of crystalline compounds inside the nanopores of open-morphology porous systems was studied on a model system, consisted of 1-octadecene and silica gels with different pore sizes, by means of thermogravimetry, differential scanning calorimetry and powder X-ray diffraction. The parameters of silica gels porous structure (surface area, pore size and volume) were calculated using N2 adsorption data. To describe the experimental results, a new thermodynamic model of crystallites melting inside the nanopores of irregular shape was established. This model allows an analytical prediction for the shift of phase transition temperature and melting enthalpy (latent heat of melting) due to the surface tension effects. To a first approximation, both parameters must linearly depend on the specific ratio of the total surface of pores to their total volume, and experimental studies have mostly confirmed this result for the melting of 1-octadecene confined inside the pores of a wide range of various silicas (with the pores of different sizes and geometry).

Determination of thermal transitions of gluten-free chestnut flour doughs enriched with brown seaweed powders and antioxidant properties of baked cookies

A protocol for determining the characteristic temperatures of thermomechanical transitions on gluten-free flour doughs is proposed. This protocol is based on the mathematical analysis of experimental curve of storage modulus (G′) vs temperature obtained by means of Dynamic Mechanical Thermal Analysis (DMTA) technique. Doughs at constant consistency of chestnut flour with different levels (3, 6 and 9% flour basis, f.b.) of brown seaweed (Bifurcaria bifurcata, Fucus vesiculosus and Ascophyllum nodosum) powders addition, 2% f.b. of guar gum and 1.8% f.b. of salt with different water absorption were used to test the proposed protocol. The ranges of temperatures corresponding to starch gelatinization (59–97 °C), amylopectin crystallites melting (82–101 °C), reversible dissociation of lipid-amylose complexes (107–128 °C) and amylose melting (133–171 °C) showed a strong dependence with water absorption of samples. Doughs with the same water absorption submitted to starch gelatinization during mixing were also analysed to corroborate the protocol suitability. Total polyphenols content and radical scavenging activity of extracts from chestnut flour-seaweed powder blends and seaweed-enriched chestnut cookies baked at 180 °C were determined. Extraction assisted with ultrasounds was carried out employing acetone-water (70:30 v/v) solution as solvent during 4 min with a liquid/solid ratio of 30 w/w. Seaweed powder addition had a positive effect on antioxidant properties of doughs before baking. However, the seaweed powder addition effect on baked products (cookies) is not clear due to antioxidant activity is overlapped by Maillard's products generated during baking.

Free volume correlation with ac conductivity and thermo-mechanical properties of poly (ethylene oxide)-silica nanocomposites

Poly(ethylene oxide), PEO, based nanocomposites are shown to have higher ionic conductivity compared to pure PEO. In order to investigate the exclusive role of free volume structure of amorphous region of PEO on its electrical conductivity, PEO-silica nanoparticles composite films have been prepared with different silica loadings. The free volume fraction of polymer composites measured using positron annihilation lifetime spectroscopy (PALS) was observed to increase nonlinearly with the increase in loading of silica. The increase in free volume on silica loading has been attributed to PEO-silica interphase as well as newly created amorphous PEO. At higher loading, positron annihilation from regions near silica particles has been confirmed by coincidence Doppler broadening measurements. Thermal analysis of polymer nanocomposites shows a decrease in crystallinity and crystallite melting temperature with the increase in silica loading. The PEO-silica nanocomposite films showed enhanced ac conductivity as well as mechanical properties (higher Young’s modulus and ductility). The observed changes in free volume structure and semicrystalline morphology of PEO matrix are attributed to the physical confinement imposed by presence of silica nanoparticles in PEO matrix. The present study shows that free volume measured using PALS has a direct relation with ac conductivity which is observed to increase drastically after a critical free volume fraction.

Status of polymorphism, physicochemical properties and in vitro digestibility of dual retrogradation-annealing modified rice starches.

In this research, for the first time, dual retrogradation-annealing modification was applied to three rice starches with 22.7%, 9.8% and 0.3% apparent amylose content (AAC). Amylose partially inhibited the effect of gelatinization on amylopectin crystallinity. Polymorphism in retrograded starches was feeble and unstable. Annealing principally caused amylopectin crystal growth by lamellar rearrangement and simultaneous degeneration of weaker lamellae. Reappearance of physical growth rings occurred. Altered crystalline arrangement had direct effect on cooked paste viscosity, gel texture, swelling power, suspension turbidity, and freeze-thaw stability of the samples. A new prominent X-ray diffraction peak (2θ = 29.1) confirmed development of novel polymorphic form other than characteristic A-, B- and V-types. Crystallite melting enthalpy (ΔH) was higher in dual modified starches (9.9 J/g, 12.9 J/g, 19.0 J/g) than native samples (ΔH = 7.4 J/g, 9.1 J/g, 12.1 J/g). Starch-lipid complexes formed the major portion of the crystalline phase within the modified starch matrices. Amylopectin played the major role in crystalline reformation and formed prominent amylopectin-lipid complexes. Simultaneous conversion of slowly digestible starch to resistant starch occurred. Enhanced thermostability, enzyme resistance and functional properties may be suitably targeted for food and non-food applications of the dual modified rice starches.

Large strain cavitation induced stress whitening in propylene-butene-1 copolymer during stretching

Large strain cavitation induced stress whitening was observed in propylene-butene-1 copolymer during stretching by means of ultra-small angle X-ray scattering technique. The critical stress for initiating this cavitation depended on the stretching temperature (Ts). A constant critical stress was found below Ts of 125 °C while the stress started to increase above 125 °C. This peculiar cavitation performance presented in propylene-butene-1 copolymer was supposed to be associated with the melting of unstable crystallites before deformation. Such unstable crystallites were normally composed of chains with co-units or short length. At the strain just before whitening, chains from those melted crystallites could recrystallize wholly into oriented crystallites as the copolymer was stretched below 125 °C while they remained molten when the sample was deformed above 125 °C. Thus, different highly oriented amorphous networks were created below and above 125 °C in copolymer, resulting in different critical stresses for large strain cavitation since this cavitation is determined by the fracture of such oriented amorphous network.