The Brill Transition in Transcrystalline Nylon-66

Improving dispersive mixing in compatibilized polystyrene/polyamide-6 blends via extension-dominated reactive single-screw extrusion

Extensional mixing elements (EMEs) that impose extension-dominated flow via stationary single-plane or double-plane hyperbolic converging-diverging channels were previously designed for twin-screw and single-screw extruders (TSE and SSE, respectively). In a recently published work by the authors, reactive extrusion was performed on PS/PA6 polymer blends TSE using EMEs and a crystalline phase transition of the minor phase in these droplets was observed as the size of droplet decreases from micron to submicron. Herein, we expand upon this work to SSE and study: a) The ability of the EMEs to improve dispersive mixing in the same blends; b) Assess the possibility of achieving the same crystalline phase transition in SSEs. The final blends were characterized by DSC, rheologically and morphologically via SEM, and the results show that while EME-based SSE leads to much improved mixing, better than non-EME TSE, the reduction in size of the PA6 disperse phase is not enough to induce the phase transition observed in EME-based TSE.

The Thermal Behavior of γ-PA1010: Evolution of Structure and Morphology in the Simultaneous Thermal Stretched Films

In this work, polyamide 1010 (PA1010) films were prepared by melt-quenching. A wide-angle X-ray diffractometer (WAXD) with a thermal stretching stage was used to investigate the structure transformation, crystallinity and degree of orientation in the course of simultaneous thermally stretched PA1010. The crystallinity increased along with the increase of draw ratio and then decreased as the draw ratio was over 2.00 times—which the maximum value reached when the draw ratio was about 2.00 times. The degree of orientation of γ-PA1010 was much greater at higher temperature than room temperature (RT); the difference gradually became weaker with the increase of draw ratio. There was a linear relationship between the draw ratios and tensile force at higher temperatures, and the tensile force increased with the increase of draw ratios. The tensile force may induce crystallization and promote orientation in the course of simultaneous thermally stretched PA1010. These phenomena are beneficial to understand the structure-processing-performance relationship and provide some theoretical basis for the processing and production.

Rediscovery of nylon upgraded by interactive biorenewable nano-fillers

Inorganic nanomaterials can only stiffen nylon with a significant loss of its toughness and ductility. Furthermore, they are not eco-friendly. In this study, the facile tuning of nylon's mechanical properties from stiff to tough was achieved, using cellulose nanocrystals (CNC) and chitosan nanowhiskers (CSW) as biorenewable fillers. The interaction between the matrix and filler was controlled by varying the types of fillers and the employed processing methods, including in situ interfacial polymerization and post-solution blending. Particularly with CSW, the in situ-incorporated filler with a 0.4 wt% loading strengthened nylon and led to a 1.9-fold increase in its Young's modulus (2.6 GPa) and a 1.7-fold increase in its ultimate tensile strength (106 MPa), whereas the solution-blended filler with a 0.3 wt% loading toughened the polymer with a 2.1-fold increase (104 MJ m^-3). Compared with inorganic nanocomposites, these interactive biofiller-nanocomposites are unrivaled in their reinforcing performance when normalized by filler content. This stiff-to-tough tuning trend is more pronounced in the CSW system than in the CNC system. Covalent polymer grafts on the amine surface of CSW enhanced interfacial interactions in the in situ method, whereas its cationic surface charges plasticized the polymer matrix in the blending method. This proteinaceous composite-mimicking all-organic nylon nanocomposite opens new possibilities in the field of reinforced engineering plastics.

Crystalline Structures and Structural Transitions of Copolyamides Derived from 1,4-Diaminobutane and Different Ratios of Glutaric and Azelaic Acids

Copolyamides derived from even 1,4-butanediamine and different mixtures of odd dicarboxylic acids with a great difference in the number of methylene groups (i.e., glutaric and azelaic acids with 3 and 7 groups, respectively) have been synthesized, characterized and structurally studied. Calorimetric analyses revealed a complex behavior with multiple melting peaks associated to lamellar reordering and the presence of defective crystals. Equilibrium melting temperatures were evaluated and showed a eutectic behavior with composition. Copolymers were able to crystallize even for samples with comonomer percentages close to 50%. Negative and ringed spherulites from the melt state and small lath-like lamellar crystals from dilute solution crystallizations were attained. Furthermore, calorimetric data pointed out the exclusion of the less abundant monomer from the lattice of the predominant structure. All samples at room temperature showed a similar crystalline structure (form I) defined by two predominant reflections at spacings close to 0.430 and 0.380 nm, which has been related for even-odd nylons with a two-hydrogen bonded structure. Real time synchrotron experiments showed that melt crystallized samples have two polymorphic transitions on heating, which were practically reversible and consequently were also detected during cooling from the melt state. Interestingly, a different behavior was detected among solution crystallized samples and specifically the transition to the intermediate structure (form II) was not detected during heating for samples enriched on the azelate component or more precisely when they were exclusively crystallized in the form I.

Thermally Induced Structural Transitions of Nylon 4 9 as a New Example of Even⁻Odd Polyamides

Crystalline morphology and structure of nylon 4 9 have been studied by means of optical and transmission electron microscopies, and X-ray diffraction. Rhombic crystals were characteristic of crystallization from glycerin dilute solutions, although the final morphology was dependent on the crystallization temperature. In any case, a single electron diffraction pattern was always obtained, being characteristic a 2 mm symmetry and reflections at spacings that were indicative of a projected rectangular unit cell with hydrogen bonds established along two planar directions (i.e., the diagonals of the unit cell), as it was determined from related polyamides. Crystallization from the melt gave rise to negative birefringent spherulites with a morphology (axialitic, speckled or ringed) that was dependent on the crystallization temperature. Kinetic analysis indicated that melt crystallization took place according to two growth mechanisms (Regimes II and III), which reflect distinct secondary nucleation rates. A complex polymorphic behavior on heating and cooling processes was evidenced by real time synchrotron experiments, being determined an intermediate crystalline structure as well as the typical pseudohexagonal arrangement associated to the Brill transition. Polymorphic transitions were highly dependent on the initial crystalline structure, being enhanced the structural transition from the low temperature structure to the intermediate one when traces of the latter were initially present. Calorimetric and infrared studies supported also the detected thermal transitions of nylon 4 9.

Investigation of the Brill transition in nylon 6,6 by Raman, THz-Raman, and two-dimensional correlation spectroscopy

The Brill transition is a phase transition process in polyamides related with structural changes between the hydrogen bonds of the lateral functional groups (CO) and (NH). In this study, we have used the potential of Raman spectroscopy for exploring this phase transition in polyamide 6,6 (nylon 6,6), due to the sensitivity of this spectroscopic technique to small intermolecular changes affecting vibrational properties of relevant functional groups. During a step by step heating and cooling process of the sample we collected Raman spectra allowing us from two-dimensional Raman correlation spectroscopy to identify which spectral regions suffered the largest influence during the Brill transition, and from Terahertz Stokes and anti-Stokes Raman spectroscopy to obtain complementary information, e.g. on the temperature of the sample. This allowed us to grasp signatures of the Brill transition from peak parameters of vibrational modes associated with (CC) skeletal stretches and (CNH) bending, and to verify the Brill transition temperature at around 160°C, as well as the reversibility of this phase transition.

Self-Associated Polyamide Alloys with Tailored Polymorphism Transition and Lamellar Thickening for Advanced Mechanical Application

Long chain polyamides with various number of methylene units in recurring amide groups, PA1012 and PA612, were blended to combine their unique advantages. The Brill transition and accompanied lamellar thickening were investigated by in situ wide angle X-ray scattering (WAXS) and small angle X-ray scattering. From WAXS patterns, the transformation from the α- to γ-crystalline phase, known as "Brill transition", can be independently observed in the constituent phases of the long chain polyamide alloys (LCPAs) during heating. A constant T_b (ca., 100 °C) irrespective of the blend composition and proportional variations of the phase content was obtained. Additionally, with elevated temperature, a gradual increase in both the crystalline layer (L_c) and amorphous layer (L_a) was detected in constituent polyamides. The compositional independence of the Brill transition in LCPAs and similar lamellar thickening originate from the complete immiscibility of both polyamides, which share stronger intramolecular rather than intermolecular hydrogen-bonding interaction and hence exhibit self-association. Contributed by the γ phase, with less extended structure and increased lamellar thickness with compact stacking, LCPAs with controlled strength and flexible features can be achieved, which can be utilized in advanced mechanical applications, particularly for hoses of automobiles. The unusually linear compositional dependence of mechanical parameters makes it possible to tailor the polymorphic and tensile properties.

Comparative Variable Temperature Studies of Polyamide II with a Benchtop Fourier Transform and a Miniature Handheld Near-Infrared Spectrometer Using 2D-COS and PCMW-2D Analysis

The main objective of this communication is to compare the performance of a miniaturized handheld near-infrared (NIR) spectrometer with a benchtop Fourier transform near-infrared (FT-NIR) spectrometer. Generally, NIR spectroscopy is an extremely powerful analytical tool to study hydrogen-bonding changes of amide functionalities in solid and liquid materials and therefore variable temperature NIR measurements of polyamide II (PAII) have been selected as a case study. The information content of the measurement data has been further enhanced by exploiting the potential of two-dimensional correlation spectroscopy (2D-COS) and the perturbation correlation moving window two-dimensional (PCMW2D) evaluation technique. The data provide valuable insights not only into the changes of the hydrogen-bonding structure and the recrystallization of the hydrocarbon segments of the investigated PAII but also in their sequential order. Furthermore, it has been demonstrated that the 2D-COS and PCMW2D results derived from the spectra measured with the miniaturized NIR instrument are equivalent to the information extracted from the data obtained with the high-performance FT-NIR instrument.