Crystallization kinetics and melting behavior of PEEK were studied by differential scanning calriometry (DSC) and modulated differential scanning calriometry (MDSC). The isothermal crystallization was performed in DSC between 290 and 320¢XC. The Avrami constants (n1, n2) and the level off time were determined from the Avrami analysis. The n1 values varied from 1.50 to 2.98, and the n2 values were between 0.52 and 1.37. The minimum induction time required for the occurrence of double melting peaks was obtained by increasing the isothermal crystallization time in a interval per minute. It was found that the minimum time was always longer than the level off time, which cannot be used as the delimitation for the occurrence of single or double melting peaks. To study the melting behavior and the mechanisms of double melting peaks, the samples after melting at 400¢XC for 15 min were crystallized isothermally between 200 and 320¢XC for 10 or 60 min, and then they were heated to 380¢XC at 10 or 2 ¢XC/min, respectively. From the MDSC results of crystallization temperatures between 280 and 310¢XC, it is found that two different morphologies and melting-recrystallization phenomenon coexisted. As the isothermal crystallization temperature increased from 280 to 310¢XC, the contribution of melting-recrystallization to the upper melting peak gradually decreased. In the case of 320¢XC, the mechanisms of double melting peaks were dominated by two different morphologies only. Quasi-isotropic composites in the stacking sequence of [0/¡Ó45/90]2s were fabricated by a modified diaphragm forming apparatus. Three different processing conditions were used to prepare AS4/PEEK composites with the same crystallinity but different transcrystallinity. The morphology before and after the long-term tensile-tensile tests was observed by means of scanning electron microscope. The transcrystallinity has no significant effect on the short-term tensile test. This was due to the fibers in the 0¢X plies of [0/¡Ó45/90]2S laminates dominated the failure at high stress for the short-term tensile test. However, as the transcrystallinity increased, the failure cycles for the long-term tensile test became longer. This expressed that the delay of damage initiation in the 90¢X and ¡Ó45¢X plies of [0/¡Ó45/90]2s led to a longer failure cycles in the long-term tensile tests.

Composites are widely used in an increasing number of applications in diverse fields. However, most traditional composite materials are difficult to recycle. Because of their enhanced recyclability, thermoplastic single-polymer composites (SPCs), i.e., composites with fiber and matrix made from the same thermoplastic polymer, have attracted much attention in the recent years. High-performance polymer fibers in combination with same polymer matrices would lead to a fully recyclable single polymer composite that has major ecological advantages. However, because a single polymer is involved in the composite, thermoplastic SPCs manufacturing presents a unique set of technical problems, and different approaches from those in standard composites manufacturing are frequently needed. Two specific issues in SPCs manufacturing are how to produce distinct forms of the same polymer and how to consolidate them. So far, most investigations have been reported on a single-component hot compaction method and two-component molecular methods. However, in these methods, either the processing window is too narrow or some impure materials are introduced into the system. The key issue in thermoplastic SPCs processing is how to melt-process the matrix without significantly annealing or even melting the fiber. To overcome the above drawbacks in existing SPCs processing, particularly to widen the SPCs processing temperature window and to purify the SPCs, a novel SPCs manufacturing process utilizing the characteristics of slowly crystallizing polymers was developed and investigated. Highly oriented and highly crystalline fibers made of a slowly crystallizing polymer are mixed with the amorphous form of the same polymer and then consolidated together under heat and pressure. In this dissertation research, two slowly crystallizing polymers, poly(ethylene terephthalate) (PET) and poly(lactic acid) (PLA), were used as model systems for SPCs processing.. To study the deformation and failure mechanisms of PET and PLA SPCs, the SPCs were characterized using tensile test, tearing test, impact test, SEM, optical microscopy, and other methods. The change of crystallinity and orientation of the material forms during SPCs processing were characterized by DSC and XRD. The effects of major process conditions on the performance of the SPCs were studied. It was found that the processing temperature played a profound role in affecting the fiber-matrix bonding property. The compression molded SPCs exhibited enhanced mechanical properties. For the PET SPCs with 45% by weight fiber content the tensile strength is four folds of that of non-reinforced PET. After reinforcement, the tearing strength of the PLA SPCs is almost an order higher than that of the non-reinforced PLA. The fusion bonding behavior of two crystallizable amorphous PET sheets was also studied. Several characterization methods including SEM, TEM and polarized microscopy (either on etched or on non-etched samples) were used to observe interfacial bonding morphology of the crystallizable amorphous PET sheets. For a bonded sample, a layer of transcrystals with a thickness of 1-2 Ým was found right at the interface. A secondary but much larger zone with a distinct morphology was observed outside the transcrystal layer. With increase of the heating time, the width of the whole interfacial region decreases. The interfacial morphology was found to significantly affect the interfacial bonding quality. The testing results further indicated that high bonding temperature with an appropriate holding time promotes interfacial bonding of two crystallizable amorphous PET.

The ferro-, pyro- and piezoelectric properties of poly(vinylidene fluoride-co-trifluoroethylene) P(VDF-TrFE) have created interest with regard to its application in aqueous and ambient surroundings for sensors, functional coatings, and in the field of life sciences. P(VDF-TrFE) thin films are usually applied via spin-coating, but dip-coating will be advantageous especially for irregularly shaped substrates. The morphology of dip- and spin-coated semi-crystalline thin films is studied as a function of both the film thickness and the annealing temperature. The characterization of the films is carried out by grazing incidence wide-angle X-ray scattering (GIWAXS), X-ray reflectometry (XRR), and infrared reflection absorption spectroscopy (IRRAS). Atomic force microscopy measurements (AFM) are used to examine the resulting topography. It is found that both spin- and dip-coated thin films crystallize in the desired edge-on orientation, but the overall crystallinity after dip-coating is decreased compared to the spin-coated films of comparable thickness and the resulting roughness is increased. The higher roughness is most probably caused by the slower evaporation of the solvents and a secondary crystallization process at the air-polymer interface.