Rigid Amorphous Phase Research Articles

Crystallization-Controlled Structure and Thermal Properties of Biobased Poly(Ethylene2,5-Furandicarboxylate).

Crystallization-controlled structure and thermal properties of biobased poly(ethylene 2,5-furandicarboxylate) (PEF) were studied. The cold-crystallization temperature controlled the structure and thermal properties of the biobased PEF. The melting was complex and evidenced the presence of a significant fraction of less-stable crystals with a low melting temperature that linearly increased with Tc, which formed already during the early stages of crystallization, together with those melting at a higher temperature. Low Tc resulted in the α'-phase formation, less crystallinity, and greater content of the rigid amorphous phase. At high Tc, the α-phase formed, higher crystallinity developed, the rigid amorphous phase content was lower, and the melting temperature of the less-stable crystals was higher; however, slight polymer degradation could have occurred. The applied thermal treatment altered the thermal behavior of PEF by shifting the melting of the less stable crystals to a significantly higher temperature. SEM examination revealed a spherulitic morphology. A lamellar order was evidenced with an average long period and small average lamella thickness, the latter about 3-3.5 nm, only slightly increasing with Tc.

Tailoring the mechanical and rheological properties of poly(lactic acid) by sterilizing UV-C irradiation

In this study, we irradiated amorphous (A) and semi-crystalline (SC) poly(lactic acid) (PLA) with different UV-C doses up to 2214 kJ/m2. We achieved an average crystallinity of 43 % by heat treatment, which was unaffected by UV-C irradiation. Modulated differential scanning calorimetry showed that crystal polymorphs and the ratio of rigid amorphous and mobile amorphous phases were also unaffected. Using gel permeation chromatography analysis, we showed that the degradation mechanism was noncatalytic random scission, and the initial molar mass was reduced by >90 % at a dose of 2214 kJ/m2 for both A- and SC-PLA samples. Our Raman spectroscopy results indicated that the probability of the formation of oxygen-containing groups increases with increasing UV-C doses. Since we found that the mechanical properties of PLA films can be tailored with UV-C light, we proposed a method to predict the overall tensile curve as a function of the UV-C dose. We also proposed a modified Cross-WLF model to describe the effect of UV-C irradiation on viscosity up to 55 % molar mass reduction. The models allow us to estimate the limits of recyclability and reusability of sterilised PLA products.

Progress in 3D printing of recycled PET

Filaments from blends of post-industrial, low-quality recycled poly(ethylene terephthalate) (RPET) and ethylene-butyl-acrylate-glycidyl-methacrylate (EBA-GMA) were extruded with different EBA-GMA contents, then specimens were 3D-printed by fused filament fabrication technology. It has been demonstrated that, when 0–90° layer order is applied, at 15 wt% EBA-GMA content the unnotched impact strength increases by two and a half times and the notched impact strength by nine times compared to samples printed from elastomer-free RPET. DSC and DMA measurements proved that EBA-GMA reactively bonds to PET molecules, which is indicated by the increment of rigid amorphous phase and glass transition temperature and the reduction of crystallinity. The co-polymer molecules formed in-situ during compounding create a Toughening Enhancer Interphase (TEI), which also remains after 3D printing and effectively enhances impact strength. The strain at break and tensile strength of the filaments are substantially higher than that of 3D-printed specimens due to the increasing shrinkage and the resulting increased porosity of the printed specimens with higher EBA-GMA content. However, the Young-modulus values are quite similar. The flexural strength of the 3D-printed specimens reaches 40–60% of the values of injection moulded samples. The proposed method enables the production of parts with arbitrary geometry and balanced mechanical properties from RPET, which may substitute acrylonitrile butadiene styrene.

Development of an Engineering Material with Increased Impact Strength and Heat Resistance from Recycled PET

The goal of the research was the concurrent enhancement of the impact strength and the heat resistance of recycled poly(ethylene terephthalate) (RPET). The morphology and the dynamic mechanical properties were examined at 0-5-10-15% ethylene-butyl-acrylate-glycidyl methacrylate (PTW) elastomer contents. The blends were crystallized for different time periods (0-20-40-60-180 s) at 150 °C and the morphology change during crystallization and its effect on impact resistance, stiffness, and thermal resistance were examined taking the three-phase model: crystalline fraction/mobile amorphous fraction/rigid amorphous fraction (CRF/MAF/RAF) into consideration. Based on DSC analyses it is proposed that before crystallization, the polymer chains covalently linked to PTW molecules contribute to the rigid amorphous phase (RAF). During thermal annealing, the relaxation of segments (which increases mobility) and ordering into crystals (which decreases mobility) have a complex effect and their resultant determines the ratio of the three phases and thereby also the macroscopic properties of the blends. After annealing the 15% PTW containing RPET blend at 150 °C for 180 s, a fivefold increase in notched impact resistance and a 50-fold increase in thermal resistance (expressed as E90’ value) were achieved compared to the neat RPET reference.

Crystal structure dependent tensile properties of silicone rubber: Influence of aluminium hydroxide

Aluminium hydroxide (ATH) filled silicone rubber working in a wide temperature range has to experience the crystallization process in many cases, in which mechanical properties would change greatly and its safety operation is threatened. In this paper, the structure-tensile properties relationship study of ATH filled silicone rubber from melting to crystallized state was carried out. By the differential scanning calorimetry (DSC) and broadband dielectric spectroscopy (BDS), it was found that ATH promoted heterogeneous nucleation in silicone rubber. With the increase of ATH, the proportion of rigid amorphous phase decreases. Meanwhile, the over doped ATH reduces the perfection of crystals during isothermal crystallization at −60 °C. Consequently, the elongation at break of high-content ATH filled silicone rubber with less crystalline and rigid amorphous phase dropped sharply by about 97% due to the failure of lamellae slips, which should arouse great attention for safety operation of ATH filled silicone rubber. It is thereby suggested to take the elongation at break as one of the criteria for the selection of ATH filled silicone rubber used in extremely low temperature.

Miscibility and rigid amorphous phase in blends of polypropylene with poly(propylene‐co‐ethylene)

AbstractThermal and mechanical properties of binary blends of polypropylene (PP) with a statistical copolymer (85 wt% propylene and 15 wt% ethylene, abbreviated here as VM) have been investigated. Both components were found to be miscible in the melt in the whole range of compositions. No separate domains of VM have been detected by polarizing optical microscopy, and the size of spherulites is going down with increasing VM content. The crystallization temperature of PP as detected by DSC, is going down to 83°C, for PP/VM blends 10:90. This is another evidence for miscibility in the melt. Viscoelastic properties of the melt were measured. Regarding the solid state, the melting enthalpy is exactly proportional to the PP content in the blend. The DSC step height at the glass transition is exactly proportional to the VM content. These results are suggesting a three‐phase model (crystalline, rigid amorphous, and mobile amorphous phase), where the VM component is mainly located in the mobile amorphous regions, while the amorphous part of PP is in the rigid amorphous regions. Stress–strain curves show a systematic increase of elongation at break with increasing VM%, to be extended from 7.8% to more than 550%.

Enthalpy relaxation of unconstrained and constrained amorphous phase for low isotacticity polypropylene

The influence of crystallization on the amorphous phase of low isotacticity polypropylene (LT-PP) was studied by analyzing the enthalpy relaxation behavior using fast scanning calorimetry (FSC) and temperature modulated FSC. The high temperature shift of the enthalpy recovery peak and the glass transition temperature during crystallization was interpreted as a transformation of the unconstrained amorphous (UCA) to constrained amorphous (CA) phase. Enthalpy relaxation approach had the same result as the conventional heat capacity analysis of mobile amorphous (MA) phase as proposed by Wunderlich. Our study revealed that successive glass transition of rigid amorphous (RA) phase in a three-phase model and the gradual increase in the heat capacity of the MA phase in a two-phase model are experimentally indistinguishable above the crystallization temperature.

The 3-Phase Structure of Polyesters (PBT, PET) after Isothermal and Non-Isothermal Crystallization.

According to the 3-phase model, semi-crystalline thermoplastics consist of a mobile amorphous fraction (MAF), a rigid amorphous fraction (RAF), and a crystalline fraction (CF). For the two polyesters Polybutylene Terephthalate (PBT) and Polyethylene Terephthalate (PET), the composition of these phases was investigated using the largest possible variation in the isothermal and non-isothermal boundary conditions. This was performed by combining the conventional Differential Scanning Calorimetry (DSC) with the Fast Scanning Calorimetry (FSC). From the results it can be deduced that the structural composition of both polymers is characterised by a large fraction of the rigid amorphous phase. This is mainly formed either during the primary crystallization in the low temperature range or during the subsequent secondary crystallization that follows primary crystallization in the high temperature range. Depending on the thermal history, the fraction of the mobile amorphous phase of both polymers approaches a minimum, which does not appear to be undercut.

The effect of the melt-drawing ratio on the microstructure and mechanical properties of poly(butylene succinate) cast films with row-nucleated lamellar structure

High-performance PBS films can be prepared by the melt-stretching method. The effect of the melt-drawing ratio (MDR) on the mechanical properties and microstructure of PBS cast films prepared by melt-stretching is studied in this paper. The elastic modulus, tensile stress, and strain hardening increase with increasing MDR. With an MDR of 25–50, the crystalline morphology changes from deformed spherulites to row-nucleated lamellar structure. The lateral size and orientation of the lamellae apparently improve with the MDR. When the MDR is within 50–125, the row-nucleated lamellar structure improves slightly by increasing the lateral size and orientation of the lamellae. The component fraction and thickness of the mobile (MAF) and rigid (RAF) amorphous fractions and crystalline phase are nearly unchanged within the whole MDR range. The increases in lateral size and orientation improve the mechanical properties of the films. Significantly, the linear relationship between the elastic modulus and orientation at MDRs from 50 to 125 indicates that the elastic modulus is determined by the crystal orientation in PBS cast films with row-nucleated lamellae. This work evaluates the importance of orientation for microstructure and properties of PBS films, which may guide the processing of high-performance PBS films.

Aliphatic polyamides (nylons): Interplay between hydrogen bonds and crystalline structures, polymorphic transitions and crystallization

Aliphatic polyamides (nylons) constitute a family of polymers with outstanding properties and multiple applications. Despite the intensive research studies carried out with nylons, there are still multiple unsolved questions concerning crystallization processes, crystalline structures, polymorphic transitions, and crystalline morphologies. Constrains imposed by the strong intermolecular interactions affect the amorphous state, the rigid amorphous phase, the molecular folding, the morphology and obviously the crystalline structure. Some of these relevant points are discussed in the present work.

Dual-Crystallizable Silk Fibroin/Poly(L-lactic Acid) Biocomposite Films: Effect of Polymer Phases on Protein Structures in Protein-Polymer Blends.

Biopolymer composites based on silk fibroin have shown widespread potential due to their brilliant applications in tissue engineering, medicine and bioelectronics. In our present work, biocomposite nanofilms with different special topologies were obtained through blending silk fibroin with crystallizable poly(L-lactic acid) (PLLA) at various mixture rates using a stirring-reflux condensation blending method. The microstructure, phase components, and miscibility of the blended films were studied through thermal analysis in combination with Fourier-transform infrared spectroscopy and Raman analysis. X-ray diffraction and scanning electron microscope were also used for advanced structural analysis. Furthermore, their conformation transition, interaction mechanism, and thermal stability were also discussed. The results showed that the hydrogen bonds and hydrophobic interactions existed between silk fibroin (SF) and PLLA polymer chains in the blended films. The secondary structures of silk fibroin and phase components of PLLA in composites vary at different ratios of silk to PLLA. The β-sheet content increased with the increase of the silk fibroin content, while the glass transition temperature was raised mainly due to the rigid amorphous phase presence in the blended system. This results in an increase in thermal stability in blended films compared to the pure silk fibroin films. This study provided detailed insights into the influence of synthetic polymer phases (crystalline, rigid amorphous, and mobile amorphous) on protein secondary structures through blending, which has direct applications on the design and fabrication of novel protein–synthetic polymer composites for the biomedical and green chemistry fields.

Plasticization of Poly(3-hydroxybutyrate-co-3-hydroxyvalerate) with an Oligomeric Polyester: Miscibility and Effect of the Microstructure and Plasticizer Distribution on Thermal and Mechanical Properties.

In the last few decades, many efforts have been made to make poly(3-hydroxybutyrate) (PHB) and its copolymers more suitable for industrial production and large-scale use. Plasticization, especially using biodegradable oligomeric plasticizers, has been one of the strategies for this purpose. However, PHB and its copolymers generally present low miscibility with plasticizers. An understanding of the plasticizer distribution between the mobile and rigid amorphous phases and how this influences thermal, mechanical, and morphological properties remains a challenge. Herein, formulations of poly(hydroxybutyrate-co-valerate) (PHBV) plasticized with an oligomeric polyester based on lactic acid, adipic acid, and 1,2-propanediol (PLAP) were prepared by melt extrusion. The effects of the PLAP content on the processability, miscibility, and microstructure of the semicrystalline PHBV and on the thermal, morphological, and mechanical properties of the formulations were investigated. The compositions of the mobile and rigid amorphous phases of the PHBV/PLAP formulations were easily estimated by combining dynamic mechanical data and the Fox equation, which showed a heterogeneous distribution of PLAP in these two phases. An increase in the PLAP mass fraction in the formulations led to progressive changes in the composition of the amorphous phases, an increase of both crystalline lamellae and interlamellar layer thickness, and a decrease in the melting and glass transition temperatures as well as the PHBV stiffness. The Flory–Huggins interaction parameter varied with the formulation composition in the range of −0.299 to −0.081. The critical PLAP mass fraction of 0.37 obtained from thermodynamic data is close to the value estimated from dynamic mechanical analysis (DMA) data and the Fox equation. The mechanical properties showed a close relationship with the distribution of PLAP in the rigid and mobile amorphous phases as well as with the microstructure of the crystalline phase of PHBV in the formulations.

Tunable Biodegradable Polylactide-Silk Fibroin Scaffolds Fabricated by a Solvent-Free Pressure-Controllable Foaming Technology.

Polylactide (PLA) and silk fibroin (SF) are biocompatible green macromolecular materials with tunable structures and properties. In this study, microporous PLA/SF composites were fabricated under different pressures by a green solid solvent-free foaming technology. Scanning electron microscopy (SEM), dynamic mechanical analysis (DMA), differential scanning calorimetry (DSC), X-ray diffraction (XRD), thermogravimetric (TG) analysis, and Fourier transform infrared (FTIR) spectroscopy were used to analyze the morphology, structure, and mechanical properties of the PLA/SF scaffolds. The crystalline, mobile amorphous phases and rigid amorphous phases in PLA/SF composites were calculated to further understand their structure-property relations. It was found that an increase in pore density and a decrease in pore size can be achieved by increasing the saturation pressure during the foaming process. In addition, changes in the microcellular structure provided PLA/SF scaffolds with better thermal stability, tunable biodegradation rates, and mechanical properties. FTIR and XRD analysis indicated strong hydrogen bonds were formed between PLA and SF molecules, which can be tuned by changing the foaming pressure. The composite scaffolds have good cell compatibility and are conducive to cell adhesion and growth, suggesting that PLA/SF microporous scaffolds could be used as three-dimensional (3-D) biomaterials with a wide range of applications.

A literature survey of the influence of preform reheating and stretch blow molding with hot mold process parameters on the properties of PET containers. Part I

The paper presents a wide analysis of the literature on the modified blow molding process with simultaneous stretching of PET [poly(ethylene terephthalate)] material for storing hot filled drinks. The paper is a continuation of the first part presented earlier [1]. In this part it is presented in detail the impact of stretch blow molding with hot mold process parameters on thermal resistance of PET containers. An analysis of the literature shows that the relaxation of the amorphous phase has the greatest impact on the thermal stability and pressure resistance of the bottle. At the same time, the thermal stability of the bottle increases, and the pressure strength decreases when the relaxation of the amorphous phase is increased, and the crystallites increase to the largest size possible without causing thermal whitening of the material. The measure of relaxation of the amorphous phase is based on the amount of oriented and “rigid” amorphous phase, since the higher the degree of relaxation of the amorphous phase, the smaller the amounts of oriented and rigid amorphous phase. The main parameters of the hot mold SBM process that affect the properties of the hot filling bottle are the intrinsic viscosity of the preform material, the power profile of the heating lamps in the heating oven (there are seven levels of heating lamps), the heating time in the oven and the associated time of temperature-induced crystallization prior to the SBM process, the speed of the stretching rod, the pre-blow delay due to the stretching rod position, the pre-blow pressure, pre-blow duration, air blow pressure, duration of the main blow, temperature profile of the heated blow mold (there are two heat zones for the blow mold, the lateral surface of the bottles and base zone), duration of annealing in the mold, cooling air temperature of a bottle in a blow mold fed by a stretching rod, and the pressure in the feed branch for air cooling of a bottle in a blow mold fed by a stretching rod. Thus, the properties of a bottle or hot fill can be influenced by as many as 20 factors during the SBM process with a hot mold.

One-step regulating the microstructure in physical foaming process of polypropylene

ABSTRACT In this work, the innovative bimodal insulating polypropylene (PP) foam was produced through a straightforward one-step mechanism with only one blowing agent, supercritical CO2. Based on differential scanning calorimetry (DSC) data, as well as scanning electron microscopy (SEM) images, it was deduced that the induced-crystallinity of PP at the start of the foaming process could determine the final foam structure predominantly. In the amorphous region, the rigid amorphous phase, which is profoundly affected by the temperature of the foaming process and also the polymer chain configurations, can accommodate nano-sized cavities, while more extensive cells can grow throughout the flexible amorphous region having higher mobility.The bimodal foam morphology is developed in a certain proportion of the rigid amorphous and flexible amorphous phase.

Toward a better understanding of the low-temperature reversible aging phenomenon in asphalt binder

ABSTRACT Asphalt aging with time is one of the main causes that leads to the performance deterioration of asphalt pavement. Compared with non-reversible oxidation aging, reversible aging which resulted from molecular structuring gets little attention in asphalt materical specification, especialy at low-temperature. This paper aims to compare the effect of oxidation and isothermal conditioning on original asphalt binder’s low-temperature properties. Firstly, the mechanisms of asphalt reversible aging are systematically reviewed in this paper. Secondly, extended bending beam rheometer (Ex-BBR) test and modulated differential scanning calorimetry (MDSC) test are carried out on original asphalt and its oxidative residue. The results show that oxidation has apparently different influence on two physical hardening indicators used in this study. Only three days of non-accelerated physical hardening may produce a more brittle material than accelerated oxidative residue. There is an obvious peak around 25°C in non-reversing heat flow curve of asphalt binder after long-term isothermal conditioning, and it is caused by some imperfect crystals forming fully crystallized structure after long-term conditioning. Both long-term isothermal conditioning and oxidation will increase the amount of crystalline phase and rigid amorphous phase.

Influence of interfaces on the crystallization behavior and the rigid amorphous phase of poly(l-lactide)-based nanocomposites with different layered doubled hydroxides as nanofiller

Based on the three-phase model of semi-crystalline polymers, we determined all phase fractions of the NiAl-LDH/PLLA nanocomposite in dependence on the concentration of the nanofiller. Moreover, the rigid amorphous fraction (RAF) was separated into the RAFcrystal and the RAFfiller unbiasedly. A detailed comparison to the related nanocomposite system MgAl-LDH/PLLA was made considering that Mg and Ni have different atomic weights. As a first result is was found that NiAl-LDH/PLLA displays a higher crystallization rate compared to MgAl-LDH/PLLA, which is related to the different morphologies of the two nanocomposite systems. For both systems RAFcrystal devided by the degree of crystallization increases with increasing concentration of the nanofiller. This means in the case of the nanocomposites investigated here not each crystal produces the same amount of RAF, as often assumed. Also, RAFfiller increases with the concentration for both systems but in a different way. This is discussed considering again the different morphologies of both nanocomposites.

Two-process constitutive model for semicrystalline polymers across a wide range of strain rates

The presence of crystalline and amorphous phases in semicrystalline polymers presents interesting constitutive modelling challenges. In this study, a physically based, three-dimensional constitutive model has been developed for simulating a wide range of features observed in deformation and processing of semicrystalline polymers. The proposed model combines into one constitutive model such features as: multiple viscoelastic relaxation processes, very wide strain-rate range, temperature-dependence, adiabatic heating, structural rejuvenation; in addition to it being applied to a semicrystalline polymer. The constitutive mathematics is based on a one-process glass-rubber model for amorphous polymers. It adapts that model to semicrystalline polymers by extending it to two relaxation processes: one associated with the glass transition of the mobile amorphous phase; the other associated with relaxation of the crystalline fraction and its associated rigid amorphous phase. In particular, two dominant processes were identified: the α-process and the β-process. The model has been implemented numerically into a commercial finite element code through a user-defined material subroutine (UMAT). The model has been validated against compression test results carried out on polypropylene. Also, the model predicts very well the experimentally observed nonlinear rate-dependent response and post-yield de-ageing of polypropylene.

Crystallinity and Property Enhancements in Neat Polylactic Acid by Chilled Extrusion: Solid‐State Shear Pulverization and Solid‐State/Melt Extrusion

Polylactic acid (PLA) is a biopolymer of significant interest to both industry and the scientific community, but an incomplete understanding of the practical processing‐structure‐property relations is limiting its application range. The study applies alternative, chilled extrusion technologies called solid‐state shear pulverization (SSSP) and solid‐state/melt extrusion (SSME) to neat, commercial PLA, and investigates the effect of the resulting morphological features upon the thermomechanical behavior. Although conventional, heated twin‐screw extrusion leads to significant thermal degradation of PLA chains, which in turn facilitates crystal growth due to enhanced chain mobility, chilled SSSP imparts chain defects and branching, which serve as heterogeneous nucleation sites in the polymer and promotes the formation of a rigid amorphous phase. A hybrid SSME process brings unique interplay of both chain architecture effects, resulting in a synergistic thermomechanical behavior involving the α' crystal polymorph formation. POLYM. ENG. SCI., 59:E286–E295, 2019. © 2019 Society of Plastics Engineers

Rigid amorphous phase and constrained polymer chains in poly(L‐lactide) nanocomposites with carboxylated carbon nanotubes prepared via reactive melt mixing

Evaluation of constrained polymer chains and the glass transition behavior of the nanocomposite constituted by poly(L‐lactide) (PLLA) and functionalized carbon nanotubes (f‐CNTs) have been carried out. To control thermal degradation, nanocomposites were prepared via reactive melt mixing taking advantage of the capacity of carboxylic groups of both PLLA and f‐CNTs to participate in chain extension reactions. At low f‐CNT content (e.g., 0.2 and 0.5 wt%), a good dispersion of f‐CNTs was observed due to scarce bonds established between both components (i.e., the polymer matrix and the nanofiller), whereas at higher f‐CNT content (e.g., 1 wt%), a greater number of epoxy groups of the chain extender were bonded to carboxyl groups of f‐CNTs, giving rise to a highly significant crosslinking of CNT and a lower molecular weight of PLLA. Crystallinity, glass transition temperature and both the rigid polymer chains and constrained polymer chains were influenced by the dispersion state of f‐CNTs after reactive melt mixing and the thermal history (e.g., cooling rate form the melt) of samples. For evaluation of interphases between poly(lactic acid) and f‐CNTs, a simple method was developed for the considered tube‐like nanoparticles. Specifically, thicknesses of the generated interphases were calculated from DMA experiments. POLYM. COMPOS., 39:E1280–E1293, 2018. © 2018 Society of Plastics Engineers