The multiple melting behacior and lamellar morphologies of isotactic polystyrene (iPS) isothermally crystallized from the glassy state have been investigated by differential scanning calorimetry (DSC) and transmission electron microscopy (TEM).The influences of different experiment variables (such as crystallization temperature and time,heating rate) on the melting behavior of iPS are studied.The combination of thermal analysis and morphological results indicates that:(1)the ‘annealing peak’ is not associated with the melting of subsidiary crystals formed by secondary crystallization as often suggested in the literature;(2)two lamellar population with different degrees of perfection within a single lamella are responsible for the so-called double melting behavior in iPS.The partial melting and repairing (via recrystallization) of iPS crystals are observed on lamellar level by TEM observations.From the obtained calorimetric and morphological results,the applicability of several crystallization and (subsequent) melting models is discussed.

The microstructure,morphology, thermal and mechanical properties of polyamide 6/layered-silicate nanocomposites (PLSN) have been studied using X-ray diffraction (XRD),tapping-mode atomic force microscopy (AFM),differential scanning calorimetry (DSC) and tensile tests.The XRD and AFM results indicate that the organically-modified layered silicates are intercalated in the polyamide 6 (PA6) matrix.Also,the crystallization and thermal behavior of PA6 are influenced by the addition of layered silicates into polymer matrix.A silicate-induced crystal transformation from the a-form to the g-form of PA6 is confirmed by XRD and DSC,i.e.,the formation of g crystal is enhanced by the presence of silicates.In comparison to PA6,the thermal property of PLSN has been investigated using DSC.The possible origins of a new silicate-induced endothermic peak are discussed.Tensile tests show that the tensile modulus and yield strength increase while the strain-at-yield decreases with increasing clay loading.

Multiwalled carbon nanotubes (MWNTS)/nylon-6 (PA6) nanocomposites with different MWNTS loadings have been prepared by the simple melt-compounding approach.A fine and homogeneous dispersion of MWNTS throughout PA6 matrix is observed by transmission electron microscopy.Scanning electron microscopy observation on the fracture surfaces of the composites shows not only a uniform dispersion of MWNTS but also a strong interfacial adhesion with the matrix,as evidenced by the presence of many broken but strongly embedded carbon nanotubes (CNTS) in the matrix and by the absence of debonding of CNTS from the matrix.Beadlike morphology is also observed along the stretched CNTS and their bundles,probably indicating the anchoring locations of the CNTS defects (within the beads) along the tubes where the PA6 matrix has strong interfacial interactions with the CNTS,thus being favorable to stress transfer from polymer to CNTS.Mechanical testing (by tensile and nanoindentation tests as well as dynamic mechanical analysis) shows that,compared with neat PA6, the elastic modulus and the yield strength of the composite are greatly improved by about 214% and 162%,respectively,with incorporating only 2 wt % MWNTS.In addition,a unique crystallization and melting behavior of MWNTS/PA6 composites are observed and discussed by combining differential scanning calorimetry and X-ray diffraction;that is,only the R-form crystals are observed in MWNTS/PA6 composites,which is quite different from the case observed in PA6/clay nanocomposites.

The multiple melting behavior and morphologies of isotactic polystyrene (iPS) isothermally crystallized from the glassy state have been investigated by differential scanning calorimetry (DSC) and transmission electron microscopy (TEM).The combination of thermal analysis and morphological results indicates that two lamellar populations are responsible for the so-called double melting behavior in iPS.The low-temperature melting peak is attributed to the melting of less perfect (thinner or defect containing) subsidiary lamellae formed in the framework of the dominant (thicker or more perfect crystalline) lamellae upon isothermal crystallization.The high-temperature one is mainly due to the melting of the dominant thicker lamellae, and to some less extent,the melting of a recrystallized population coming from the melted defect lamellae during the heating process in DSC.