Transamidation determination and mechanism of long chain-based aliphatic polyamide alloys with excellent interface miscibility

Effective and sustainable depolymerization of Nylon 66 - a transamidation for the complete recycling of polyamides

The transamidation of polyamides with short primary amides is reported as an effective recycling technique. This novel depolymerization method is robust and only utilizes cheap and renewable reagents. The process requires a Nb2O5 catalyst, assisted by NH3, and operates at relatively mild reaction conditions (i.e. 200 °C and 3 bar NH3).

Strain-Induced Form Transition and Crystallization Behavior of the Transparent Polyamide

A transparent polyamide, poly(4,4'-aminocyclohexyl methylene dodecanedicarboxylamide) (PAPACM12), was studied and characterized by in situ wide-angle X-ray diffraction (WAXD) to establish the relationship between its crystallization behavior, crystalline form transition under external fields, and macroscopic properties. During the heating process, cold crystallization occurred and increased, and there was no form transition below the melting point. During the isothermal process, PAPACM12 exhibited the same crystalline structure as that during the heating process. The crystalline structure of PAPACM12 was attributed to α-form crystal, which is the stable form, according to the WAXD diffraction peaks of the conventional AABB-type polyamides. During stretching deformation, the crystal transition from α-form to γ-form and strain-induced crystallization were observed to contribute to the PAPACM12 with higher breaking strength and elongation. This study firstly determine the crystalline structure of transparent polyamides, and then the controlled strain-induced crystallization and transformation are demonstrated to be effective preparation methods for polyamides with high properties.

Structure characterization of a pyruvated exopolysaccharide from Lactobacillus plantarum AR307

A pyruvated exopolysaccharide designated as LPE-1 was isolated and purified from the fermentation broth of Lactobacillus plantarum AR307 and characterized for its chemical structure. The results indicated that LPE-1 contained galactopyranose (Galp) and glucopyranose (Glcp) at a molar ratio of 2: 1. The weight-averaged molecular weight (M_w) of LPE-1 was 605 kDa, with a polydispersity index (PDI) of 1.57, intrinsic viscosity ([ƞ]) of 3.28 dL/g, Mark-Houwink-Sakurada exponent α of 0.65 and gyration of radius (R_g) of 36.10 nm. The results of GC-MS and NMR revealed that pyruvate (Pyr) was found to form cyclic ketals at O-4 and O-6 position of terminal galactopyranose (T-Galp). The backbone of LPE-1 was identified to be consisted of 1,4-β-D-Glcp (23.19%), 1,4-α-D-Glcp (11.38%) and 1,4,6-β-D-Galp (12.05%), branched by 1,6-β-D-Galp (38.88%) at O-6 position of 1,4,6-β-D-Galp residue and terminated by T-β-D-Galp (5.60%) or T-β-D-(4,6-Pyr)-Galp (8.90%). A possible structural unit was proposed for LPE-1 as follows: where Galp* is either T-β-D-(4,6-Pyr)-Galp or T-β-D-Galp. The presence of pyruvate group in LPE-1 would play an important role in improving the viscosity and plasticity of dairy products.

A Facile Strategy to Fabricate Antistatic Polyamide 1012/Multi-Walled Carbon Nanotube Pipes for Fuel Delivery Applications

Developing antistatic long chain polyamide (LCPA) resins and fabricating the corresponding fuel pipes are challenges but necessary. Herein, a facile but effective strategy was put forward to fabricate LCPA resins with a superior conductivity, meeting the requirements of electrostatic sub-conductors. The strategy was based on, first, the incorporation of a large amount (15 wt%) of multi-walled carbon nanotubes (MWCNTs) into a polyamide 1012 (PA1012) matrix as a master batch, which formed a dense conductive network. Subsequently, it was diluted with PA1012 granules to produce base resins, and the reprocessed nanocomposites with a critical content of MWCNTs (3 wt%) could generate an effectively interconnected conductive network, with sparse and thinning features. Using the base resins, fuel pipes for automobiles, petrol stations and high pressure applications were successfully fabricated, where the thin conductive network was transformed into a thick one due to external field-induced re-agglomeration of MWCNTs. In this way, the obtained fuel pipes combined excellent conductive and barrier properties, and mechanical properties at high and low temperatures. These comprehensive properties also arose from the uniform dispersion of MWCNTs in an LCPA matrix, even without coupling agents; the attractive interaction between MWCNTs and the polyamide chains contributed to their strong interface adhesion. Thus, this research provides a versatile approach to fabricating antistatic LCPA resins, which will certainly extend their application to vehicle fuel systems.

Crystal Structure and Mechanical Properties of Uniaxially Stretched PA612/SiO2 Films

Stretching has a significant effect on the microstructure and ultimate performance of semi-crystalline polymers. To investigate the effect of stretching on structure and mechanical properties of uniaxial stretched PA612/SiO₂, PA612 and PA612/SiO2 films were prepared at four temperatures close to the glass transition temperature at various strain. The samples were characterized by a transmission electron microscope (TEM), wide-angle X-ray diffractometer (WAXD), Two-dimensional wide-angle X-ray Scattering (2D-WAXS), differential scanning calorimeter (DSC), dynamic mechanical analyzer (DMA), and stretching tests. The results showed that the α phase was the dominant phase in PA612 casting film, no obvious γ phase was observed, while both stretching and the presence of SiO₂ can induce the generation of α phase and improve the crystallinity of PA612. Crystals were oriented along the stretching direction and the b axis was parallel to the equatorial direction after stretching. The interplanar spacing of (010/110) decreased with the increasing stretching temperature and expanded with the increasing strain, while stretching temperature and strain present negligible effect on the interplanar spacing of (100). The grain size increased with the stretching temperature while decreased with strain. The presence of SiO₂ led to reduce the yield stress and the stress drop beyond yielding of the composite. Uniaxial stretching gave rise to a significant improvement in the fracture stress and the glass transition temperature.

High performance poly(urethane-co-amide) from CO2-based dicarbamate: an alternative to long chain polyamide

Due to its high strength, toughness, corrosion resistance and wear resistance, long chain polyamide (LCPA) has attracted broad interest. Nevertheless, its wide application in industrial fields is still being restricted because the starting material acquisition step involving diacid and diamine remains a major obstacle. Herein, we circumvent this obstacle by developing a novel polymer with similar properties by a green and efficient copolymerization process of carbon dioxide (CO₂)-based dicarbamate with diamide diol under vacuum conditions, named poly(urethane-co-amide) (PUA). The semi-crystalline PUAs with high number-weight-average molecular weights (M_n, up to 41.3 kDa) were readily obtained, and these new polymers show high thermal stability (above 300 °C). Thanks to its unique chain structure, the amide, urethane and urea groups can endow the polymer with a high density cross-linking network via hydrogen bonds and high crystallinity that can result in high strength, up to 54.0 MPa. The dynamic thermomechanical analysis (DMA) results suggest that the phase separation exists within the new polymers, endowing the PUAs with a toughness higher than that of long chain polyamides. Consequently, this work not only develops a useful new polymer like commercial polyamides with high performance as a long chain polyamide candidate, but also provides a new way of utilizating CO₂.

A novel high performance polymer like long carbon-chain nylon was synthesized via a green and efficient copolymerization from CO₂-based dicarbamate.

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.