Successive Self-nucleation And Annealing Research Articles

Improving Environmental Stress Cracking Resistance of High-Density Polyethylene Grades by Comonomer Addition and Nanocomposite Approach.

The aim of this paper is to determine the effect of polymer density, correlated to the comonomer content, and nanosilica addition on the mechanical and Environmental Stress Cracking Resistance (ESCR) characteristics of high-density polyethylene (HDPE). In this regard, five HDPE samples with similar Melt Flow Index (MFI) and molar mass but various densities were acquired from a petrochemical plant. Two polymerization reactors work in series and differ only in the amount of 1-buene comonomer fed to the second reactor. To ascertain the microstructure of the studied samples, GPC and SSA (successive self-nucleation and annealing) analyses were accomplished. All samples resulted having similar characteristics but slightly various SCB/1000 C=7.26-9.74 (SCB=Short Chain Branching). Consequently, meanwhile studied HDPEs reveal similar notched impact and stress at yield values, the tensile modulus, stress-at-break, and elongation-at-break tend to demonstrate different results with the SCB content. More significantly, ESCR characteristic varied considerably with SCB/1000 C extent, so that higher amount of SCB acknowledged advanced ESCR. Notably, blending HDPE sample containing higher amount of SCB/1000 C, with 3 wt.% of chemically modified nanosilica enhanced ESCR characteristic by 40 %. DFT (Density Functional Theory) calculations unveiled the role of the comonomer, quantitatively by binding energies and qualitatively by Non Covalent Interaction (NCI) plots.

Self-nucleation (SN) and successive self-nucleation and annealing (SSA) as powerful tools to determine the composition of polyolefin post-consumer recycled blends

For the incorporation of post-consumer recycled (PCR) resins in mechanical recycling processes, it is crucial to determine their composition accurately. The blends of linear low-density polyethylene (LLDPE) and low-density polyethylene (LDPE) in PCR film resins pose a challenge due to their varying ratios. This study introduces a quantitative method that employs the successive self-nucleation and annealing (SSA) technique to analyze commercial PCR LLDPE/LDPE blend compositions. Our method is an efficient way to assess these blend compositions, offering an improved analysis compared with traditional methods. We established a series of calibration curves based on the SSA final melting trace to validate our approach. The SSA technique's efficacy was compared with the robust NMR method, showing that SSA can predict LLDPE contents in the blends with comparable accuracy. We demonstrate that the SSA methodology is an accurate and reliable technique for assessing complex waste streams, thereby facilitating the optimization of recycling processes and advancing the goals of sustainable materials management.

Clarifying the effects of comonomer distribution between short and long chains on physical and mechanical properties of ethylenic copolymers

AbstractIn this paper, two Zigler‐Natta catalysts (ZNCs) were used to synthesize a commercially available linear low‐density polyethylene (LLDPE), widely used in the packaging industry, on an industrial scale. The catalysts differ only in their ability to distribute comonomers between short and long chains. Both catalysts were fully characterized in the first section, and two similar ethylene/1‐butene copolymers were made using them. Afterward, the produced copolymers were fully characterized using different techniques; namely, differential scanning calorimetry (DSC), successive self‐nucleation and annealing (SSA), oxygen induction time (OIT), melt flow index (MFI), rheometric mechanical spectroscopy (RMS), and a wide range of mechanical experiments. It was revealed that while the presence of comonomers in short chains can reduce their resistance against oxidation (by more than 30%) and can cause a dramatic change in friction coefficients (by more than 20%), some of the other main mechanical properties of the made copolymers were independent of comonomer distribution between long and short chains. In addition, it was shown that ethylenic copolymers' strain hardening modulus (SHM) takes advantage of the homogenous distribution.

Recent applications of the Successive Self-nucleation and Annealing thermal fractionation technique

Successive Self-nucleation and Annealing (SSA) is a thermal fractionation technique that is performed by Differential Scanning Calorimetry (DSC). The combination of non-isothermal and isothermal steps applied during SSA achieves efficient molecular segregation during polymer crystallization. Such molecular segregation magnifies the effect of defects in polymer chain crystallization, thereby providing information on chain structure. The technique was created and implemented by Müller and co-workers in 1997, becoming a powerful resource for studying ethylene/α-olefin copolymers. The different variables to design the SSA protocol: fractionation window, fractionation time, scanning rate, sample mass, and the first self-nucleation temperature to be applied (Ts, ideal), have been previously reviewed, together with the different applications of SSA. SSA versatility, simplicity (when properly applied), and short times to produce results have allowed its use to study novel and more complex polymeric systems. This review article explores the most recent applications of SSA of the past decade. First, the principles of the technique are briefly explained, covering all the relevant variables. Next, we have selected different cases that show how SSA is employed in various novel fields, such as studying intermolecular interactions and topological effects in homopolymers; supernucleation and antinucleation effects in nanocomposites, including the pre-freezing phenomenon; crystallization modes in random copolymers; solid-solid transitions; miscibility, co-crystallization and composition in blends; evaluation of polymer synthesis variables; and the novel information that could be gained by using fast scanning chip-based calorimetry. Finally, we offer a perspective on SSA, a technique that has become a powerful method for studying the distribution of defects affecting crystallization in semi-crystalline polymers.

Fractionated Crystallization Behavior of Low-Molecular-Weight Polyethylene Grafted onto SiO2Nanoparticles

The synthesis of polymer-grafted nanoparticles is crucial for the development of polymer nanocomposites with excellent properties, but the synthesis of polyethylene (PE)-grafted SiO2 nanoparticles (PE-g-SiO2 NPs) remains a significant challenge due to the chemical inertia of PE. In this study, PE-g-SiO2 NPs with different grafting densities and molecular weights were successfully synthesized by a simple “grafting to” method, and differential scanning calorimetry was used to study the crystallization behavior of grafted PE. Some PE-g-SiO2 samples exhibited three crystallization peaks in the cooling curve (i.e., fractionated crystallization phenomena). Self-nucleation (SN) and successive SN and annealing (SSA) results reveal that the nanoparticles in PE-g-SiO2 samples provoke both confinement and nucleation effects on the grafted PE chains. For PE-g-SiO2 NPs with higher grafting density and molecular weight, the PE chains are more stretched and the interfacial chain segmental dynamics are less suppressed, which enhance the nucleation effect and weaken the confinement effect.

Effect of the TrFE Content on the Crystallization and SSA Thermal Fractionation of P(VDF-co-TrFE) Copolymers.

In this contribution, we study the effect of trifluoro ethylene (TrFE) comonomer content (samples with 80/20, 75/25, and 70/30 VDF/TrFE molar ratios were used) on the crystallization in P(VDF-co-TrFE) in comparison with a PVDF (Poly(vinylidene fluoride)) homopolymer. Employing Polarized Light Optical Microscopy (PLOM), the growth rates of spherulites or axialites were determined. Differential Scanning Calorimetry (DSC) was used to determine overall crystallization rates, self-nucleation, and Successive Self-nucleation and Annealing (SSA) thermal fractionation. The ferroelectric character of the samples was explored by polarization measurements. The results indicate that TrFE inclusion can limit the overall crystallization of the copolymer samples, especially for the ones with 20 and 25% TrFE. Self-nucleation measurements in PVDF indicate that the homopolymer can be self-nucleated, exhibiting the classic three Domains. However, the increased nucleation capacity in the copolymers provokes the absence of the self-nucleation Domain II. The PVDF displays a monomodal distribution of thermal fractions after SSA, but the P(VDF-co-TrFE) copolymers do not experience thermal fractionation, apparently due to TrFE incorporation in the PVDF crystals. Finally, the maximum and remnant polarization increases with increasing TrFE content up to a maximum of 25% TrFE content, after which it starts to decrease due to the lower dipole moment of the TrFE defect inclusion within the PVDF crystals.

Thermal Fractionation of Ethylene/1-Octene Multiblock Copolymers from Chain Shuttling Polymerization

Ethylene/1-octene statistical multiblock copolymers (OMBCs) consisting of the alternation of crystalline, hard blocks and amorphous, soft blocks, with ≈0.5 and 20 mol % of 1-octene units, respectively, are subjected to thermal fractionation resorting to successive self-nucleation and annealing (SSA). The study is extended to random copolymers (RCs) of high (44 kDa) and low (3.4 kDa) number average molecular mass Mn, mimicking in 1-octene content the crystalline hard blocks and to the OMBC fractions extracted in boiling n-hexane and cyclohexane through a suitable solution fractionation protocol. For all the samples, the melting endotherms are well resolved in a multiplicity of peaks corresponding to the melting of crystals of different thicknesses generated in the SSA protocol that reflect the distribution of the methylene sequence length (MSL) in between consecutive interruptions along the chains. It is shown that, regardless of molecular mass, the MSL distributions of the RC samples are shifted toward greater values than those of the OMBC samples, and that also the shapes of the distributions are different. Since the MSL distribution depends on the frequency and distribution of the defects along the chains, and the defects act as interruption points, the higher fraction of long crystallizable sequences in the RC samples suggests that whereas for the RC samples the interruptions are merely represented by the 1-octene units that are rejected outside the crystals, for the OMBCs, the interruption of the regular methylene sequences belonging to the crystalline hard blocks due to the amorphous soft blocks linked to them should also play a role. Indeed, due to the partial miscibility of the hard and soft blocks, the hard blocks of major length tend to crystallize in a confined environment. This prevents the formation of thicker crystals and induces decrease of the MSL values as well as changes in the shape of the MSL distributions (topological confinement). On the other hand, the hard blocks of shorter length tend to crystallize, crossing the hard block rich regions and causing melting point depression and consequent shift of the MSLs toward lower values with respect to RCs (diluent effect). It is shown that differences in the MSL distribution of OMBCs are the result of the interplay between topological confinement and diluent effect, which in turn reflects differences in the OMBC chain microstructure, that is, differences in the distribution of block length at the inter- and intra-chain level.

Fast successive self‐nucleation and annealing (SSA) thermal fractionation protocol for the characterization of polyolefin blends from mechanical recycling

AbstractThe sorting stage of mechanical recycling of post‐consumer polyolefins has severe challenges. Polypropylene (PP) is often contaminated with polyethylene (PE) and vice versa. To meet quality requirements, characterization of the recycled pellets is needed. To address this problem, fast characterization generating a statistical assessment of the content of the various batches from recycling is required. This investigation shows that the use of fast scanning rates (in a conventional Differential Scanning Calorimeter) in the successive self‐nucleation and annealing (SSA) protocol can reduce the thermal fractionation time, without losing resolution power, as long as the increase in heating/cooling rate is compensated by reducing sample mass. Using a “coupled SSA protocol” for polypropylene and polyethylene fractions at a rate of 10 °C/min, the measurement time is approximately 420 min. Implementing mass compensation, faster heating rates (i.e., 30 °C/min) and using a single‐fraction protocol, sufficient to determine the content of PP and high‐density PE, reduced the time of the measurement to 75 min. Examples of fractionations of commercial post‐consumer and post‐industrial recycled polyolefin blends conducted at a faster rate are provided. The derived polyolefin content is compared with the standard temperature rising elution fractionation analysis to assess the validity of the proposed method.

Using Successive Self-Nucleation and Annealing to Detect the Solid–Solid Transitions in Poly(hexamethylene carbonate) and Poly(octamethylene carbonate)

Solid–solid transitions in poly(hexamethylene carbonate) (PC6) and poly(octamethylene carbonate) (PC8), denoted the δ to α transition, have been investigated, using self-nucleation and the successive self-nucleation and annealing (SSA) technique. The SSA protocol was performed in situ for thermal (differential scanning calorimetry (DSC)), structural (wide-angle X-ray scattering (WAXS)), and conformational (Fourier transform infrared spectroscopy (FT-IR)) characterization. The final heating after SSA fractionation displayed an enhanced (compared to a standard second DSC heating scan) endothermic and unfractionated peak signal at low temperatures corresponding to the δ to α transition. The improved (i.e., higher enthalpy and temperature than in other crystallization conditions) δ to α transition signal is produced by annealing the thickest lamellae made up by α and β phase crystals after SSA treatment. As thicker lamellae are annealed, more significant changes are produced in the δ to α transition, demonstrating the transition dependence on crystal stability and, thus, on the crystallization conditions. The ability of SSA to significantly enhance the observed solid–solid transitions makes it an ideal tool to detect and study these types of transitions. In situ WAXS reveals that the δ to α transition corresponds to a change in the unit cell dimensions, evidenced by an increase in the d-spacing. This implies a more efficient chain packing in the crystal, for both samples, in the δ phase (lower d-spacing at low temperatures) than in the α phase (higher d-spacing at high temperatures). The chain packing differences are explained through in situ FT-IR measurements that show the transition from ordered (δ phase) to disordered (α phase) methylene chain conformations.

In situ polymerization of ethylene in the presence of graphene by α‐diimine Nickel (II)/MAO catalyst system: Thermal and rheological study

In situ polymerization of ethylene with pretreated graphene nano‐platelet (GNP) was carried out by (α‐diimine nickel)/MAO catalyst system. The molecular weight of the synthesized samples was determined using rheometric mechanical spectroscopy. The number of branches and melting temperature values was evaluated by regular differential scanning calorimetry (DSC) and successive self‐nucleation and annealing (SSA) technique. According to obtained results, the molecular weight of the samples was increased from 72,730 to 260,100 g/mol for neat PE and high‐filled GNP, respectively. The number of chain branches decreased by the addition of GNP from 61.51 per 1,000 carbon atoms to 37.10 for neat PE and the sample containing 22.36 wt% of GNP. Obtained results revealed that the samples containing low branches and high molecular weight were achieved in the presence of highly loaded GNP. Also, the electrical conductivity, storage modulus, loss modulus, and complex viscosity of the samples improved by increasing GNP weight fraction.

Crystallization of poly(hexamethylene carbonate)-co-poly(hexamethylene urethane) segmental block copolymers: From single to double crystalline phases

The crystallization behavior of aliphatic poly(hexamethylene carbonate)-co-poly(hexamethylene urethane) (PHCU) segmental block copolymers was studied through non-isothermal differential scanning calorimetry (DSC) experiments at different rates, successive self-nucleation and annealing (SSA), in-situ wide-angle X-ray diffraction (WAXD), and in-situ Fourier transform infrared spectroscopy (FTIR). The crystallization and melting temperatures show linear dependence on the hexamethylene urethane content ([HU]) in PHCU copolymers with high [HU], as well as the similarities of the crystalline structure, indicated an isomorphic-like cocrystallization behavior. However, such behavior was discarded because of the sequential crystallization and sequential melting found by cooling and heating the samples at 1 °C/min, and the cold-crystallization peaks by heating the samples at 10 °C/min, specially at low [HU]. Also, bimodal SSA profiles at low [HU] (≤30 mol%) were found. The fractions at low temperatures could be assigned to the polycarbonate (PC)-rich phase, and those at high temperatures to the polyurethane (PU)-rich phase. The bimodal SSA profile was evident in the PHCU with 10 mol% [HU] (i.e., PHCU-10), which was selected for further analysis. The in-situ WAXD and in-situ FTIR results corroborated the sequential crystallization and melting of the PC- and PU-rich crystals in the PHCU-10 and can be extrapolated to [HU] as high as 30 mol%. The PHCU copolymers had a complex and rate-dependent crystallization behavior, characterized by a single crystallization of the PU-rich phase at high [HU] and double phases including crystallization of both PU- and PC-rich at low [HU].

Melt Memory Effects in Poly(Butylene Succinate) Studied by Differential Fast Scanning Calorimetry.

It is widely accepted that melt memory effect on polymer crystallization depends on thermal history of the material, however a systematic study of the different parameters involved in the process has been neglected, so far. In this work, poly(butylene succinate) has been selected to analyze the effect of short times and high cooling/heating rates that are relevant from an industrial point of view by taking advantage of fast scanning calorimetry (FSC). The FSC experiments reveal that the width of melt memory temperature range is reduced with the time spent at the self-nucleation temperature (Ts), since annealing of crystals occurs at higher temperatures. The effectiveness of self-nuclei to crystallize the sample is addressed by increasing the cooling rate from Ts temperature. The effect of previous standard state on melt memory is analyzed by (a) changing the cooling/heating rate and (b) applying successive self-nucleation and annealing (SSA) technique, observing a strong correlation between melting enthalpy or crystallinity degree and the extent of melt memory. The acquired knowledge can be extended to other semicrystalline polymers to control accurately the melt memory effect and therefore, the time needed to process the material and its final performance.

The chain microstructure and condensed structure of polyethylene resin used for Biaxially stretched film

AbstractTo explore the desirable chain structure and condensed structure of polyethylene used for biaxial stretching, the blends of two polyethylenes (PE1 and PE2) with different molecular weight and branch distribution were investigated. Their condensed structure including relaxation and crystallization behavior was studied by rheology, dynamic mechanical analysis (DMA), and non‐isothermal crystallization kinetics. And the chain microstructure was characterized by preparative temperature rising elution fractionation (P‐TREF), and successive self‐nucleation and annealing (SSA). It was demonstrated that the structural variables were not changing monotonically with the increment of the PE1 content. The longest relaxation time, lowest and less varied crystallization rate always appeared when the blend contained 15 wt% of PE1. This excellent structure was owing to the formation of more branches on the short chains, resulting in the uniform distribution of lamellae size and thus showing the widest biaxial stretchable temperature range (i.e., 8°C).

A tailor-made Successive Self-nucleation and Annealing protocol for the characterization of recycled polyolefin blends

A fast and easy-to-implement technique able to investigate the complex chemical composition of polyethylene/polypropylene (PE/PP) blends derived from recycling is required. Thermal fractionation, in particular the Successive Self-nucleation and Annealing (SSA) method, proves to be suitable for this purpose. Therefore, a new tailor-made SSA protocol, able to fractionate both PE and PP in the same temperature program, was developed. Furthermore, the fractionation of model blends with known composition allowed the assessment of the temperature regions where co-crystallization among the blend components does not occur, enabling the development of a method for the quantitative evaluation of the amount of the high melting PE component and of the PP phase in a blend. Finally, the composition of two recycled blends was successfully assessed by means of the novel quantitative method and the results were compared with those achieved by a solution-based fractionation technique on the same materials.

Photo-degradation of polyethylene under stress: A successive self-nucleation and annealing (SSA) study

Successive self-nucleation and annealing (SSA) technique based on calorimetry is utilized to reveal the effect of uniaxial tensile stress on the photo-oxidation of high density polyethylene (HDPE). Stress-induced acceleratory and inhibitory effects on HDPE are confirmed by analyzing the newly formed melting peaks at low temperatures and the gradually disappeared melting peaks at high temperatures on the SSA curves. The formation of short chains due to chain scission contributes to both the new higher melting peaks (thick lamellae) and lower melting peaks (thin lamellae) because of high mobility and thermodynamic preference, respectively. Besides, chain crosslinking also gives rise to the formation of low melting peaks due to the decrease in the crystallizable sequence lengths and dynamical constraints. Compared with Fourier Transform Infrared Spectrometry, Scanning Electron Microscopy and Small Angle X-ray Scattering, the SSA technique can more precisely and sensitively reflect the early multi-scale aging behavior of HDPE subjected to stress.

Exploring the roles of molecular structure on the β-crystallization of polypropylene random copolymer

To investigate effects of molecular structures on β-crystallization of polypropylene random copolymer (PPR), PPR-A and PPR-B with similar molecular weight and distribution but significantly different polymorphic behavior were used. Wide-angle X-ray diffraction (WAXD), Fourier transform infrared spectroscopy (FT-IR), solvent fractionation combined with successive self-nucleation and annealing (SSA) and Gel Permeation Chromatography (GPC) were applied. Results revealed that after addition of same amount of β-nucleating agent (β-NA), large amount of β-phase is obtained in PPR-A (K β = 0.603), while no β-phase can be seen from PPR-B; Structure characterizations revealed that they have similar molecular weight but different total amount and distribution of ethylene comonomer: the total content of ethylene comonomer of PPR-A is higher compared with PPR-B, but its ethylene comonomer distribution is less uniform. In this way, PPR-A possesses high molecular weight high isotactic fraction, which cannot be seen from PPR-B due to its more uniform comonomer distribution. Therefore, the presence of highly isotactic PP (HPP) is the key factor in β-crystallization of PPR. For verification, HPP with low or high molecular weights are respectively added into β-nucleated PPR-B. Results revealed that HPP was effective in enhancing β-crystallization of PPR-B; higher molecular weight of HPP was more favorable and more effective.

Crystallization behavior of precision polymers containing azobenzene defects

The crystallization of precision polymers containing (cis/trans)-azo-benzenes as defects within a polyalkylene-chain, prepared via ADMET and subsequent hydrogenation, is reported. The polymers are designed such that after exactly 18 –CH2− units an azobenzene-moiety (bearing either an o,o-dihydrogen (H-azo) or an o,o-difluorinated azo-moiety (F-azo) is placed, able to photochemically switch cis/trans configuration, thus changing the geometrical constraint exerted on the alkyl-moiety during crystallization and its crystal packing. The morphology of these polymers (Mn=3100 to 17,000g/mol) is investigated using differential scanning calorimetry (DSC), wide-angle X-ray scattering (WAXS) and successive self-nucleation and annealing (SSA) experiments, putting special emphasis on the crystallization of the alkyl moieties. H/F-azo defects within the poly(alkyl)-chains significantly increase the melting point of the polymers compared to ADMET polymers without defect. Successive self-nucleation and annealing (SSA) and WAXS analysis show inclusion of the azo-moieties into the PE crystal. Changing the aromatic azo units from hydrogen (H-azo) to fluorine (F-azo) atoms also increases the enthalpy of melting and the melting point of the azo-polymers. Photochemical trans-to-cis isomerization of the (F-azo)-polymers increases lattice disorder throughout the entire sample to an extent sufficient to disrupt the long-range structuring of the sample, thus causing the reduction in their crystallinities.

Thermal analysis and successive self-nucleation and annealing (SSA) treatment of synthesized bimodal polypropylene (BPP) reactor blends using homogeneous binary metallocene catalyst

Several polypropylene (PP) reactor blends were synthesized using homogenous binary metallocene catalytic systems composed of isospecific (I): rac-Me2Si(2-Me-4-Ph In)2ZrCl2 and oscillating (II): (2-Ph In)2ZrCl2 catalysts. The reactor blends were analyzed using gel permeation chromatography and differential scanning calorimetry. All the blends showed bimodal molecular weight distribution, and the MWs were shifted toward higher values compared with PPs synthesized with each of individual catalysts showing some probable interactions between the two active sites. Self-nucleation and annealing treatment on hexane-insoluble–heptane-soluble parts of the PP reactor blends showed that as the II/I molar ratio increases from 0 to 40 in the binary system, multiplicity of the endotherm peaks increases from 1 to 7, which is indicative of the presence of various lamellar thicknesses in the samples. Wide-angle X-ray scattering studies on the PP reactor blends confirmed that the blends have isotacticities and crystallinities between those of polymers obtained by the individual catalysts.

Application of the correct design of successive self-nucleation and annealing (SSA) to study the stereo-defects and its distribution of homo- and co-polypropylene

The SSA revealed the differences in molecular chain microstructure of different PP samples when the preliminary characterization found that the homo-polypropylene or co-polypropylene samples had the similar mechanical and thermal properties.

Probing the early stages of thermal fractionation by successive self-nucleation and annealing performed with fast scanning chip-calorimetry

The thermal fractionation kinetics of a linear low-density polyethylene (LLDPE) during Successive Self-Nucleation and Annealing (SSA) is investigated by fast scanning chip-calorimetry (FSC), by systematically varying the holding times (ts) at each fractionation temperature (Ts). The range of explored fractionation times spans four orders of magnitude, from 0.001 to 10 s. Discernible thermal fractions are already detected in the very early stages of the process, at ts shorter than one second. As ts increases, the melting endotherm after SSA indicates a progressive lamellar thickening and narrowing of the thicknesses distribution of the various crystalline fractions. The largest variations are observed for the families of crystals containing the longest crystallizable sequences, which also undergo a change of their relative content as a consequence of self-nucleated crystallization at Ts. The quality of the thermal fractionation obtained in 10 seconds with FSC is equivalent to that of conventional differential scanning calorimetry SSA (ts = 300 s). © 2016 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2016, 54, 2200–2209