Fast Scanning Chip Calorimetry Research Articles

New Insights into Crystallization of Heterophasic Isotactic Polypropylene by Fast Scanning Chip Calorimetry.

The crystallization kinetics of metallocene-catalyzed heterophasic isotactic polypropylene composed of a matrix of isotactic polypropylene (iPP) and rubbery particles made of random ethylene–propylene copolymers (EPC), often denoted as heterophasic iPP copolymers, was analyzed as a function of the cooling rate and supercooling in nonisothermal and isothermal crystallization experiments, respectively. Fast scanning chip calorimetry (FSC) allowed assessing crystallization at processing-relevant conditions, and variation of the content (0–39 wt %) and composition (0–35 wt % propylene counits) of the EPC particles revealed qualitatively new insight about mechanisms of heterogeneous crystal nucleation. For neat iPP homopolymer, the characteristic bimodal temperature dependence of the crystallization rate due to predominance of heterogeneous and homogeneous crystal nucleation at high and low temperatures, respectively, is reconfirmed. At high temperatures, in heterophasic iPP, the here studied ethylene-(C2)-rich EPC particles accelerate crystallization of the iPP-matrix, with the acceleration or nucleation efficacy correlating with the EPC-particle content. The crystallization time reduces by more than half in presence of 39 wt % EPC particles. An additional nucleating effect of the EPC particles on iPP-matrix crystallization is detected after their crystallization, suggesting that liquid/rubbery particles are less effective than solid/semicrystalline particles in affecting crystallization of the surrounding iPP-matrix. At low temperature, homogeneous crystal nucleation in the iPP-matrix outpaces all heterogeneous nucleation effects, and the matrix-crystallization rate is independent of the sample composition. The obtained results lead to the conclusion that the crystallization kinetics of iPP can be affected significantly by the content and composition of EPC particles, even towards superfast crystallizing iPP grades.

Steady-State Crystal Nucleation Rate of Polyamide 66 by Combining Atomic Force Microscopy and Fast-Scanning Chip Calorimetry

Homogeneous crystal nucleation in polyamide 66 (PA 66) was studied by a combination of atomic-force microscopy (AFM) and fast-scanning chip calorimetry (FSC), with a specific experimental setup all...

The chain dis-entanglement effect of polyhedral oligomeric silsesquioxanes (POSS) on ultra-high molecular weight polyethylene (UHMWPE)

The nanoparticles small enough can significantly altered segmental dynamic and chain relaxation of polymer. The viscoelastic properties of ultrahigh molecular weight polyethylene (UHMWPE) blended with polyhedral oligomeric silsesquioxanes (POSS) was investigated in detail. A reduced viscosity of UHWMPE/Octamethyl- POSS was observed. The mechanism of viscosity reduction was studied from the view of disentanglement effect. Dynamic mechanical analysis (DMA) indicated that the pseudoequilibrium modulus (GN0) of UHMWPE/POSS (100/0.5) blend in the rubbery plateau was much lower than that of UHMWPE. Accordingly, the calculated entanglement density (Me) of UHMWPE/POSS blend was smaller than that of pure UHMWPE. Further reduction in glass transition temperature (Tg) was observed by the differential scanning calorimeter (DSC). Additionally, isothermal annealing was conducted on UHWMPE using differential fast scanning chip calorimetry (Flash-DSC) firstly. Two melting peaks of the sample were observed after isothermal melt-crystallization and the data were analyzed using the modified Arrhenius equation. The sample UHWMPE/POSS showed a lower melting active energy than pure UHWMPE, indicating the entanglement level of UHMWPE decreased and chain segment activity improved with addition of a small amount of POSS.

Effects of amide comonomers on polyamide 6 crystallization kinetics

Amide comonomers are common in proteins, which bring chemical confinement to their beta-folding. Furthermore, co-polymerization is a common industrial way to enhance polymer properties. By means of fast-scanning chip-calorimetry (Flash DSC) measurement, we investigated how various amide comonomers (amide 6,6 and amide 12) influence the isothermal crystallization kinetics of polyamide 6. The results show that both amide-6-based random copolymers containing separately 18 mol% of amide 6,6 and 20 mol% of amide 12 crystallize slower than polyamide 6 due to the structural mismatching of amide comonomers in hydrogen-bonding interactions, reflecting the general chemical confinement of co-monomers in copolymer crystallization. However, in the low temperature region, the copolymer holding amide 12 crystallizes even slower than the copolymer holding amide 6,6, opposite to what we usually expected for a higher mobile comonomer of amide 12. We found that the anomalous behavior could be attributed to the temperature region where polyamide 12 crystallizes still slower than polyamide 6,6. Our wide-angle X-ray diffraction results revealed that those amide comonomers retain the habits of their corresponding homopolymers in copolymer crystallization due to their inclusion in the crystalline phase of polyamide 6.

Fingerprints of homogeneous nucleation and crystal growth in polyamide 66 as studied by combined infrared spectroscopy and fast scanning chip calorimetry

Homogenous crystal nucleation and growth in polyamide 66 (PA66) are followed in situ by means of a combination of FTIR spectroscopy and fast scanning chip calorimetry (FSC). Therefore, a novel setup with a calorimetry chip equipped with an IR-transparent SiN membrane was developed, which enables to examine IR spectroscopic and FSC experiments on the identical specimen. Because of the small amount of sample material (~ 100 ng), it is possible to achieve heating and cooling rates up to 5000 Ks−1, and hence to quench the sample into a fully amorphous state without quenched-in homogeneous crystal nuclei. Annealing the film then allows to determine the onset of homogenous nucleation and crystal growth by means of FSC, whereas molecular interactions are unraveled by FTIR spectroscopy. It is demonstrated that different moieties of PA66 respond distinctly during crystallization; far-reaching interactions such as hydrogen bonding are established prior to onset of short-range steric hindrance.Graphical Crystal nucleation and growth are followed in situ by means of a combination of FTIR spectroscopy and fast scanning chip calorimetry. For this purpose a novel IR-transparent chip enables to examine both measurements on the identical specimen, while heating and cooling rates up to 5000 Ks−1 and hence quenching into a fully amorphous state can be achieved

Stability of Crystal Nuclei of Poly (butylene isophthalate) Formed Near the Glass Transition Temperature.

Tammann’s two-stage crystal-nuclei-development method is applied for analysis of the thermal stability of homogenously formed crystal nuclei of poly(butylene isophthalate) (PBI) as well as their possible reorganization on transferring them to the growth temperature, using fast scanning chip calorimetry. Crystal nuclei were formed at 50 °C, that is, at a temperature only slightly higher than the glass transition temperature, and developed to crystals within a pre-defined time at the growth temperature of 85 °C. The number of nuclei, overcritical at the growth temperature, was detected as a function of the transfer-conditions (maximum temperature, heating rate) by evaluation of the developed crystal fraction. For different size-distributions of crystal nuclei, as controlled by the nucleation time, there is detected distinct reduction of the nuclei number on heating to maximum temperatures higher than about 90 to 110 °C, with the latter value holding for longer nucleation time. Longer nucleation allows for both increasing the absolute nuclei number and generation of an increased fraction of larger nuclei. Heating at 1000 K/s to 140–150 °C causes “melting” of even the most stable nuclei. While direct transfer of crystal nuclei from the nucleation temperature (50 °C) to the growth temperature (85 °C) reveals negligible effect of the transfer-heating rate, in-between heating to higher temperatures is connected with distinct nuclei-reorganization above 85 °C on heating slower than 1000–10.000 K/s. The performed study not only provides specific valuable information about the thermal characteristics of crystal nuclei of PBI but also highlights the importance of proper design of Tammann’s nuclei development experiment for analysis of nuclei numbers. With the evaluation of critical rates of temperature-change for suppression of non-isothermal formation of both nuclei and crystals, the kinetics of crystallization of the slow crystallizing PBI is further quantified.

Crystal nucleation in poly(ether ether ketone)/carbon nanotube nanocomposites at high and low supercooling of the melt

The engineering thermoplastic poly(ether ether ketone) (PEEK) has a rigid backbone that crystallizes relatively slowly upon cooling the melt. In this study, fast scanning chip calorimetry (FSC) was used to analyze isothermal crystallization between 170 and 285 °C, a range from about 27 K above the glass transition temperature up to the melting temperature. Incorporation of carbon nanotubes (CNT) enhances nucleation at all crystallization temperatures, including low temperatures. FSC also was employed to study crystallization at cooling rates spanning 0.33 to 8000 K/s, important as PEEK is subject to these conditions during melt processing. The critical cooling rate to produce a vitrified sample was increased from 500 K/s in the neat PEEK to 4000 K/s in a 5% CNT/PEEK nanocomposite due to faster nucleation rate caused by heterogeneous nucleation.

Polymorphism and Multiple Melting Behavior of Bio-Based Poly(propylene 2,5-furandicarboxylate).

Furandicarboxylate-based polyesters are considered an interesting class of bio-based polymers due to their improved properties with respect to the petrol-based terephthalate homologs. An in-depth analysis of the crystal structure of poly(propylene 2,5-furandicarboxylate) (PPF), after maximum possible removal of the catalyst, was carried out. The study disclosed that purified PPF presents two different crystalline phases after crystallization from the melt. Crystallizations at temperatures lower than 120 °C lead to growth of a single crystal form (β-form), whereas two different crystal forms (α and β) were found to coexist at higher Tcs. This behavior is opposite to that previously observed for unpurified PPF. The possibility that the catalyst nucleates the α-phase, which therefore becomes the kinetically favored modification at low crystallization temperatures in the presence of a higher amount of catalyst residue, has been considered as a feasible explanation. Two concomitantly different spherulitic morphologies were observed and connected to the β- and α-phase, respectively. The association between polymorphism and melting behavior was studied. The origin of the peaks that compose the multiple melting endotherm recorded at conventional heating rates was determined by combined wide-angle X-ray scattering, differential scanning calorimetry, fast scanning chip calorimetry, and polarized light optical microscopy measurements. The higher thermal stability of the α-crystals in comparison with the β-form was thus demonstrated.

Formation and stabilization of crystal nuclei in isotactic polybutene-1 aged below glass transition temperature

Aging of glassy isotactic polybutene-1 (iPB-1) below the glass transition temperature (Tg) leads to remarkable acceleration of the subsequent isothermal crystallization due to the promotion of crystal nuclei. The formation and development of crystal nuclei during aging below Tg and during heating to the crystallization temperature have been probed by fast scanning chip calorimetry. The size and stability of the crystal nuclei change with the aging time. A short aging below Tg can only induce nuclei with small sizes which can grow into bigger stable ones during the heating process above Tg if the heating rate is not high enough. With a prolonged aging time below Tg, bigger stable nuclei can also be developed, and its number increases till reaches a maximum value. These results suggest that noncooperative local motions rather than cooperative segmental motions in glassy iPB-1 are responsible for the formation of crystal nuclei during aging below Tg.

Melt Crystallization of Poly(butylene 2,6-naphthalate)

Poly(butylene 2,6-naphthalate) (PBN) is a crystallizable linear polyester containing a rigid naphthalene unit and flexible methylene spacer in the chemical repeat unit. Polymeric materials made of PBN exhibit excellent anti-abrasion and low friction properties, superior chemical resistance, and outstanding gas barrier characteristics. Many of the properties rely on the presence of crystals and the formation of a semicrystalline morphology. To develop specific crystal structures and morphologies during cooling the melt, precise information about the melt-crystallization process is required. This review article summarizes the current knowledge about the temperature-controlled crystal polymorphism of PBN. At rather low supercooling of the melt, with decreasing crystallization temperature, β’- and α-crystals grow directly from the melt and organize in largely different spherulitic superstructures. Formation of α-crystals at high supercooling may also proceed via intermediate formation of a transient monotropic liquid crystalline structure, then yielding a non-spherulitic semicrystalline morphology. Crystallization of PBN is rather fast since its suppression requires cooling the melt at a rate higher than 6000 K·s−1. For this reason, investigation of the two-step crystallization process at low temperatures requires application of sophisticated experimental tools. These include temperature-resolved X-ray scattering techniques using fast detectors and synchrotron-based X-rays and fast scanning chip calorimetry. Fast scanning chip calorimetry allows freezing the transient liquid-crystalline structure before its conversion into α-crystals, by fast cooling to below its glass transition temperature. Subsequent analysis using polarized-light optical microscopy reveals its texture and X-ray scattering confirms the smectic arrangement of the mesogens. The combination of a large variety of experimental techniques allows obtaining a complete picture about crystallization of PBN in the entire range of melt-supercoolings down to the glass transition, including quantitative data about the crystallization kinetics, semicrystalline morphologies at the micrometer length scale, as well as nanoscale X-ray structure information.

Enthalpy Relaxation of Polyamide 11 of Different Morphology Far Below the Glass Transition Temperature

Polyamide 11 (PA 11) samples of different supermolecular structure, including the crystal-free glass and semi-crystalline PA 11 of largely different semi-crystalline morphology, were prepared by fast scanning chip calorimetry (FSC). These samples were then annealed at different temperatures well below the glass transition temperature Tg. The main purpose of the low-temperature annealing experiments was the calorimetric detection of mobility of chain segments at temperatures as low as −40 °C (≈Tg − 80 K) where still excellent impact resistance is predicted. It was found that annealing PA 11 at such low temperature, regardless the thermal history and supermolecular structure including crystallinity as well as crystal shape and size, permits distinct enthalpy relaxation at rather short time scale with the structural changes reverting on subsequent heating as detected with pronounced sub-Tg-enthalpy-recovery peaks. The main glass transition, associated to large-amplitude segmental mobility, as well as relaxations at temperatures only slightly below Tg are even more distinctly sensitive to the crystal morphology. In contrast to spherulitically grown lamellar crystals, presence of high-specific-surface area nanometer-sized ordered domains causes a shift of the glass transition temperature of the amorphous phase to higher temperature, proving stronger coupling of ordered and amorphous phases than in case of lamellae. In addition, the increased coupling of the crystalline and amorphous phases slows down the cooperative rearrangements on annealing the glass slightly below Tg. The performed study contributes to further understanding of the spectrum of structural relaxations in PA 11 including the effect of presence of crystals. Enthalpy relaxation and consequently the reduction of entropy at temperatures slightly below Tg strongly depends on the semi-crystalline morphology, while an only minor effect is seen on low-temperature annealing at Tg − 80 K, possibly indicating different molecular mechanisms for the processes occurring in both temperature ranges. The low-temperature process even seems proceeding in the crystalline fraction of the material.

Crystal self-nucleation in polyamide 11 of different semicrystalline morphology

Self-nuclei supported recrystallization of the crystal-free melt of polyamide 11 (PA 11) of qualitatively different initial semicrystalline morphology, either containing nodular crystals or spherulitically grown lamellar crystals, has been investigated by fast scanning chip calorimetry, optical microscopy and atomic force microscopy. Melt-recrystallization of PA 11 initially containing a large number of nodules of high surface-to-volume ratio and strong coupling to the surrounding amorphous structure, as confirmed with the detection of significant amount of rigid amorphous fraction, is distinctly faster than melt-recrystallization of PA 11 initially containing lamellae and spherulites, caused by a lower number of self-nuclei in the latter system. Moreover, the temperature range of survival of self-nuclei above the respective melting temperature of nodular and lamellar crystals is larger for PA 11 initially containing nodules. The melt-residence time, within the assessable time-range before onset of melt-recrystallization, has no effect on the self-nuclei number. Enhanced self-nucleation in PA 11 containing nodules, compared to spherulitically crystallized PA 11, is suggested being caused by the distinctly larger initial number of individually grown crystals. A possible effect of the rigid amorphous fraction, forming during nodular crystallization, on hindering relaxation of the melt is discussed.

Assessment of Crystallinity Development during Fused Filament Fabrication through Fast Scanning Chip Calorimetry

Although semi-crystalline polymers are associated with considerably better mechanical properties and thermal stability compared to their amorphous counterparts, using them as feedstock for Fused Filament Fabrication still poses some major challenges. Hence, the development of printed part crystallinity during printing should be fully understood in order to control the developed weld strength, as well as part shrinkage and warpage. Infrared thermography was utilized to record the thermal history of deposited layers while printing a single-layer wall geometry, employing two PA 6/66 copolymers with distinct molecular weights as feedstock. Print settings were varied to establish which settings are essential to effectively monitor final part crystallinity. The resulting temperature profiles were simulated in a Fast Scanning Chip Calorimetry device that allows for the rapid heating and cooling rates experienced by the printed polymer. Both liquefier temperature and print speed were found to have very little influence on the total attained crystallinity. It became apparent that the build plate, set at a temperature above the polymer’s glass transition temperature, imposes a considerable annealing effect on the printed part. A reduced molecular weight was observed to enhance crystallinity even more strongly. The presented methodology proves that Fast Scanning Chip Calorimetry is an effective tool to assess the impact of both print parameters and feedstock characteristics on the crystallization behavior of semi-crystalline polymers over the course of printing.

Effect of supercooling on crystal structure of nucleated isotactic polypropylene

The present study focuses on the crystallization behavior and structure formation of isotactic polypropylene (iPP) containing polymeric nucleating systems. Poly(vinyl cyclopentane) (PVCP) and poly(vinyl cyclohexanе) (PVCH) were pre-polymerized on the catalyst particle before propylene polymerization. Non-isothermal crystallization experiments were performed by standard differential scanning calorimetry (DSC) and by fast scanning chip calorimetry (FSC) at cooling rates in the range from 10−1 to 103 K/s. Wide angle X-ray scattering (WAXS) was employed to collect information regarding the crystal structure of samples with a specific cooling history prepared in FSC. Both nucleating agents, PVCP and PVCH, led to acceleration of crystallization and increase of the temperature range of α-phase crystallization of iPP. Most striking was the result that in presence of PVCH at concentrations lower than 30 ppm, it was possible to crystallize iPP in the stable monoclinic form in the complete range of processing relevant cooling rates.

Melt-recrystallization of poly (l-lactic acid) initially containing α′-crystals

The kinetics of melt-recrystallization and the stability of crystal self-nuclei of poly (l-lactic acid) initially containing disordered α′-crystals with a melting temperature of around 150 °C has been analyzed using specifically designed fast scanning chip calorimetry experiments (FSC). In general, the rate of recrystallization of the melt after complete melting of α′-crystals decreases with increasing melt-temperature mainly due to the lowering of the self-nuclei concentration. Self-nuclei of highest stability survive up to about 170 °C. The concentration of self-nuclei/α′-crystal remnants at a specific melt-temperature between 150 and 170 °C is independent on time, that is, only the temperature of the melt controls the self-nuclei content. Combining fast scanning calorimetry with polarized-light optical microscopy and with atomic force microscopy allows studying the semicrystalline morphology of samples of different self-nucleation history, providing direct information about the self-nuclei concentration in the various melts.

Competitive growth of crystalline form II and form I in isotactic Polybutene-1

The competitive growth of form II and form I in isotactic polybutene-1(PB-1) was investigated with fast scanning chip calorimetry. By systematically varying the isothermal time, the pre-crystallized PB-1 samples with different crystallinity of form II are obtained and then used to study the competition between the growth of form II and the transformation of form II into form I. All the samples were annealed at 258 K for 60s to help nucleation of form I so that fast transformation could be performed. Crystal transformation kinetics results indicated that the competitive growth of form II and form I can be classified into three regimes. When the crystallinity of form II is small enough, fast transformation from form II to form I does not take place, attributed to lacking of the nuclei of form I as the degree of internal stress is extremely low. This suggests that only certain strength of internal stress and certain crystallinity of form II enable the nucleation of form I and then promote the transformation from form II to form I. With increasing crystallinity of form II, both fast transformation and slow transformation are observed. When crystallinity of form II further increases, only fast transformation is observed. However, the transition rate decreases and then reaches a plateau, resulting from the rearrangement of polymer chains and the increasing regularity of form II, indicating that the increasing regularity of form II inhibits the transformation from form II to form I.

Cover Image: Nucleation‐controlled semicrystalline morphology of bulk polymers

The crystal nucleation pathway is of huge importance for tailoring the semicrystalline morphology of polymers. For demonstration, the cover images show samples of the biopolymer poly (l-lactic acid) crystallized at 130 °C (bottom row) and 140 °C (top row), with the crystallization temperature approached by direct cooling of the melt (right-column images), or on heating after prior nucleation at 60 °C (left-column images). In their review article e10036, Christoph Schick and René Androsch present an overview of research activities evaluating the link between the nucleation-history and semicrystalline morphology, covering numerous polymers and including results obtained using fast scanning chip calorimetry as an extremely useful tool for precisely assuring specific nucleation pathways. As illustrated by the cover images, the combination of chip calorimetry and microscopy conveys quantitative information about the relation between the thermal history and the resulting morphology. (DOI: 10.1002/PCR2.10036)

Effect of surface modification on the dispersion, rheological behavior, crystallization kinetics, and foaming ability of polypropylene/cellulose nanofiber nanocomposites

Herein, the issue of dispersing cellulose nanofiber (CNF) in hydrophobic polymer has been solved through the modification of the CNF surface using alkenyl succinic anhydride (ASA). Polypropylene (PP) nanocomposites containing CNF with various degrees of substitution (DS)−ranging from 0 to 0.4−were prepared by melting and blending in an extruder. Fourier transform infrared spectroscopy (FTIR) results illustrated that the ASA chains were successfully incorporated into the CNF, and the FTIR spectroscopic imaging and X-ray computed tomography demonstrated the well-dispersed hydrophobic-modified CNF with the highest DS (=0.4) in the PP matrix. Rheological results revealed that a network-like structure of CNF was generated in the PP/CNF nanocomposites. Compared with isotactic PP, the PP/CNF composites exhibited improved crystallization kinetics, which could be elucidated via fast scanning chip calorimetry (FSC) analysis. Finally, the foaming performance of the prepared composites was examined using an easily scaled foam injection molding technique. The incorporation of CNF remarkably ameliorated the cellular morphologies of PP foams, resulting in a sharp decrease in cell size and a notable enhancement in cell density.

Fully Bio-Sourced Nylon 11/Raw Lignin Composites: Thermal and Mechanical Performances

Ecofriendly fully bio-composites based on polyamide 11 (PA11) and lignin have been prepared on the entire concentration range using a twin-screw extruder. In this work, PA11 was blended with lignin by direct extrusion technology without any chemical pre- or in-situ- modifications or physical pretreatments. The presence of various organic and inorganic impurities in the selected technical lignin have been maintained. The incorporation of this cheap renewable material from biomass in bio-based PA11 was inspected by an array of characterization tools. Also, the effect of the presence of lignin on the morphology and on the mechanical properties of the resulting materials was examined. Finally, in-situ investigation of structural evolution in PA11 induced by the presence of lignin was analyzed by Fast Scanning Chip Calorimetry.

Molecular structure and driving force to metastable states: Janus faces in polymer crystallization

AbstractThis paper is a retrospective of a past dedicated to research on polymers and a situation sketch of the present and the near future. (Co)polymers discussed are mainly based on ethylene. (Cross‐)fractionation techniques combined with state‐of‐the‐art characterization techniques, like quantitative differential scanning calorimetry, are powerful tools for the study of the links between two main topics: molecular structure and crystallization/melting. These form the two ‘Janus faces’ polymers can show, namely Face 1: the molecular structure resulting from polymerization with the keyword ‘nature’; and Face 2: the driving force of crystallization towards a metastable state, with the keyword ‘nurture’. After all, to meet demands for properties of products, in principle one starts with a given molecular architecture, after which dedicated processing, including application of temperature–time ramps, has to do the job. With new instrumentation, especially fast scanning (chip) calorimetry, for the first time in history the driving force towards crystallization into one of the possible metastable states – via Face 2 – can be controlled, of course within certain limits given by Face 1. This promising outlook of combining the faces to a useful symbiosis of Janus will be a challenge for those working in the science of crystallization of polymers. © 2018 Society of Chemical Industry