Study of polymer film formation and their characterization using NMR, XRD and DSC

Die Bildung dünner Polymerschichten aus den umweltfreundlichen Polymeren Gelatine, Stärke und Poly(vinylalkohol) (PVOH) wurde mit Hilfe von Kernspinresonanz (NMR), Weitwinkel-Röntgendiffraktometrie (XRD) und Differential-Scanning-Kalorimetrie (DSC) untersucht. Die Proben wurden durch Abguss wässriger Polymerlösungen hergestellt und ihr Trocknungsprozess bei Raumtemperatur mit Hilfe eines unilateralen NMR-Scanners bis zur vollständigen Erstarrung untersucht. Eindimensionale Tiefenprofile mit mikroskopischer Auflösung wurden zu verschiedenen Stadien des Prozesses aufgenommen. Jeder Profilpunkt wurde dabei aus der Summe mehrerer Spin-Echos gebildet. Weiterhin wurden aus der Abnahme der Echointensitäten für jeden Punkt Spin-Spin-Relaxationszeiten (T2) bestimmt und in Bezug auf den Trocknungsprozess interpretiert. Darüber hinaus wurden Spin-Gitter-Relaxationszeiten (T1) gemessen. Abhängig vom Typ und der ursprünglichen Konzentration des untersuchten Polymers wurden während der Verdunstung des Lösungsmittels unterschiedliche molekulardynamische Prozesse in verschiedenen Tiefen der Schicht beobachtet. Die Ergebnisse zeigen eine räumliche Inhomogenität der molekulardynamischen Prozesse während der Trocknung. Im fortgeschrittenen Stadium des Trocknungsprozesses beeinflusst diese Inhomogenität die mikroskopische Anordnung der Polymerketten während der Erstarrung und bestimmt somit die endgültige Struktur der Polymerschicht. XRD-Messungen der vollständig erstarrten Schichten bestätigen die von den NMR-Messungen aufgezeigte strukturelle Inhomogenität.Film formation and their characterization of three eco-friendly polymers, namely gelatin, starch and poly(vinyl alcohol) (PVOH) were studied using nuclear magnetic resonance (NMR), wide-angle X-ray diffractometry (XRD) and differential scanning calorimetry (DSC) techniques. Polymer solutions were prepared using water as a solvent followed by casting. The drying process of the cast sample was monitored at room temperature with a single-sided NMR scanner until complete solidification occurred. Depth-dependent NMR profiles with microscopic resolution were acquired at different stages of sample drying. Each profile point was accumulated from the echo decay. Spin-spin relaxation times (T2) were measured from the echo decays at different layers and were correlated with the drying process during film formation. Additionally, spin-lattice relaxation times (T1) were determined. Depending on the polymer studied and the initial concentration of each polymer, different types of molecular dynamics were observed at different heights during evaporation of the solvent. The study indicates that each polymer shows a spatial heterogeneity in the molecular dynamics during drying. In the advanced stage of drying process, the microscopic arrangement of the polymer chains during their solidification is influenced by this dynamic heterogeneity and determines the final structure of the film. XRD of the film in its final state confirmed the structural heterogeneity identified by the NMR

Effect of initial conformation on the starch biopolymer film formation studied by NMR

The formation of a rigid porous biopolymer scaffold from aqueous samples of 1% w/v (suspension) and 5% w/v (gel) corn starch was studied using optical and nuclear magnetic resonance (NMR) techniques. The drying process of these systems was observed using a single-sided NMR scanner by application of the Carr–Purcell–Meiboom–Gill pulse sequence at diffrent layer positions. The echo decays were analyzed and spin–spin relaxation times (T2) were obtained for each layer. From the depth dependent T2 relaxation time study, it was found that the molecular mobility of water within the forming porous matrix of these two samples varied notably at diffrent stages of film formation. At an intermediate stage, a gradual decrease in mobility of the emulsion sample towards the air–sample interface was observed, while the gel sample remained homogeneous all along the sample height. At a later stage of drying, heterogeneity in the molecular dynamics was observed in both samples showing low mobility at the bottom part of the sample. A wide-angle X-ray diffraction study confirmed that the structural heterogeneity persisted in the final film obtained from the 5% corn starch aqueous sample, whereas the film obtained from the 1% corn starch in water was structurally homogeneous

Comparative studies of mechanical and interfacial properties between jute and bamboo fiber-reinforced polypropylene-based composites

Jute and bamboo fiber-reinforced polypropylene (PP) based composites (50wt% fiber) were fabricated by compression molding. Tensile strength (TS), bending strength (BS), tensile modulus (TM), and bending modulus (BM) of the jutereinforced PP composite were found to be 48, 56, 900, and 1500 MPa, respectively. Then, bamboo fiber-reinforced PP-based composites (50 wt% fiber) were fabricated and the mechanical properties evaluated. The TS, BS, TM, and BM of bambooreinforced PP composites were found to be 60, 76, 4210, and 6210 MPa, respectively. It was revealed that bamboo fiber-based composites had higher TS, BS, TM, and BM compared to jute-based composites. Degradation tests of the composites (jute fiber/PP and bamboo fiber/PP) were performed in soil at ambient conditions for up to 24 weeks. It was revealed that bamboo fiber/PP composite retained its original mechanical properties higher than that of jute fiber/PP composite. The interfacial shear strength of the jute and bamboo fiber-based composites was investigated using the single-fiber fragmentation test and it was found to be 2.14 and 4.91 MPa, respectively. Fracture sides of the composites were studied by scanning electron microscope, and the results revealed poor fiber matrix adhesion for jute fiber-based composites compared to that of the bamboo fiber-based composites

Polymer/Carbon Nanotubes (CNT) Nanocomposites Processing Using Additive Manufacturing (Three-Dimensional Printing) Technique: An Overview

Additive manufacturing (AM)/3D printing (3DP) is a revolutionary technology which has been around for more than two decades, although the potential of this technique was not fully explored until recently. Because of the expansion of this technology in recent years, new materials and additives are being searched for to meet the growing demand. 3DP allows accurate fabrication of complicated models, however, structural anisotropy caused by the 3DP approaches could limit robust application. A possible solution to the inferior properties of the 3DP based materials compared to that of conventionally manufactured counterparts could be the incorporation of nanoparticles, such as carbon nanotubes (CNT) which have demonstrated remarkable mechanical, electrical, and thermal properties. In this article we review some of the research, products, and challenges involved in 3DP technology. The importance of CNT dispersion in the matrix polymer is highlighted and the future outlook for the 3D printed polymer/CNT nanocomposites is presented

Polymer/Carbon Nanotubes (CNT) Nanocomposites Processing Using Additive Manufacturing (Three-Dimensional Printing) Technique: An Overview

Additive manufacturing (AM)/3D printing (3DP) is a revolutionary technology which has been around for more than two decades, although the potential of this technique was not fully explored until recently. Because of the expansion of this technology in recent years, new materials and additives are being searched for to meet the growing demand. 3DP allows accurate fabrication of complicated models, however, structural anisotropy caused by the 3DP approaches could limit robust application. A possible solution to the inferior properties of the 3DP based materials compared to that of conventionally manufactured counterparts could be the incorporation of nanoparticles, such as carbon nanotubes (CNT) which have demonstrated remarkable mechanical, electrical, and thermal properties. In this article we review some of the research, products, and challenges involved in 3DP technology. The importance of CNT dispersion in the matrix polymer is highlighted and the future outlook for the 3D printed polymer/CNT nanocomposites is presented

Study of the Formation of Poly(vinyl alcohol) Films

The film formation of poly­(vinyl alcohol) of different molecular weights from concentrated solution has been observed in real time by means of low-field nuclear magnetic resonance (NMR) methods. The drying of films was followed with a depth resolution of 50 μm up to the formation of the final film of typically 300 μm thickness, and the molecular mobility was determined with spatial resolution by analyzing the NMR relaxation times (<i>T</i>₂, <i>T</i>₁) behavior. A gradient in the molecular dynamics was observed from <i>T</i>₁ data during evaporation process up to an intermediate time when the film shrinkage rate decreases significantly; <i>T</i>₂ indicates dynamical heterogeneity as well, persisting up to complete removal of water. The relaxation times suggest an increase of local molecular order which is more pronounced toward the air/film interface. Wide-angle X-ray diffraction confirms the formation of an ordered region at this interface with a crystallinity higherdepending on molecular weightthan at the bottom side of the film

Polyacrylonitrile solution homogeneity study by dynamic shear rheology and the effect on the carbon fiber tensile strength

Poly(acrylonitrile-co-methacrylic acid) (PAN-co-MAA)/N,N-dimethylformamide (DMF) solutions were prepared and dynamic shear rheology of these solutions were investigated. With increasing stirring time up to 72 h at 70??C, the polymer solution became less elastic (more liquid-like) with a ???60% reduction in the zero-shear viscosity. Relaxation spectra of the PAN-co-MAA/DMF solutions yield a decrease in relaxation time (disentanglement time, ??d), corresponding to an about 8% decrease in viscosity average molecular weight. The log-log plot of G??? (storage modulus) versus G??? (loss modulus) exhibited an increase in slope as a function of stirring time, suggesting that the molecular level solution homogeneity increased. In order to study the effect of solution homogeneity on the resulting carbon fiber tensile strength, multiple PAN-co-MAA/DMF solutions were prepared, and the precursor fibers were processed using gel-spinning, followed by continuous stabilization and carbonization. The rheological properties of each solution were also measured and correlated with the tensile strength values of the carbon fibers. It was observed that with increasing the slope of the G??? versus G??? log-log plot from 1.471 to 1.552, and reducing interfilament fiber friction during precursor fiber drawing through the addition of a fiber washing step prior to fiber drawing, the carbon fiber strength was improved (from 3.7 to 5.8 GPa). This suggests that along with precursor fiber manufacturing and carbonization, the solution homogeneity is also very important to obtain high strength carbon fiber. POLYM. ENG. SCI., 56:361&#8211;370, 2016. &copy; 2016 Society of Plastics Engineer