High‐density polyethylene layered silicate nanocomposites: Effect of mechanical stretching on the crystal‐to‐crystal transformations, morphology, and extent of exfoliation

Abstract

High‐density polyethylene/clay nanocomposites were elongated until breakage to investigate the effect of the mechanical stretching on the crystal‐to‐crystal transformations and their morphology. Crystalline transformations of the polymer matrix were studied via Fourier transform infrared spectroscopy, differential scanning calorimetry, and X‐ray diffraction measurements. It was concluded that the stress‐induced crystal‐to‐crystal transformations from orthorhombic structures to monoclinic and pseudohexagonal structures as well as the back‐transformation during relaxation were hindered by the presence of the clay. X‐ray diffraction studies on stretched samples showed that the mechanical stretching led from an intercalated structure to an almost exfoliated structure. These findings agreed with scanning electron micrographs, in which the beneficial effect of stretching on the exfoliation of the clay was evident. © 2006 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 44: 914–924, 2006

Infrared spectroscopy as a tool to monitor the extent of intercalation and exfoliation in polymer clay nanocomposites

“…The ratios of the peak at 1040 cm À1 over the one at 1050 cm À1 increases (0.42-0.47) after melt mixing owing to the intercalation [24] of the polymer chains between the clay platelets. After the stretching of the sample the ratio decreases down to 0.17-0.…”

“…The preferential orientation of the peak at 1085 cm À1 cannot be justified unless it is supposed that it is attributed to the dismantling of the platelets by the intercalated polymer chains during their alignment leading to the exfoliation of the clay. The stressed-induced exfoliation of the clay platelets for this nanocomposite has already been shown via X-ray measurements and scanning electron microscopy imaging of cryo-fractured samples [24]. In addition, recent studies on linear low-density polyethylene (LLDPE) have verified the stressinduced exfoliation in blown LLDPE/Fusabond/Cloisite 15A composites [9].…”

“…18. This decrease appears to be a result of the exfoliation of the clay as it has been monitored by X-ray measurements and SEM imaging [24]. In other words, the effect of the vibration owing to exfoliated clays is rather low and therefore the transition from an intercalated to an exfoliated structure results in its reduction.…”

“…Scanning electron microscopy imaging of an unstretched cryofractured sample with 1% of clay [24] has shown that the clay platelets are oriented parallel to the surface. The light beam direction is perpendicular to the plane of the film, so the polarization, i.e.…”

Biaxial deformation behavior and mechanical properties of a polypropylene/clay nanocomposite

“…A further study, in which the solid state elongational behavior of high density polyethylene and its structure-properties were examined, concluded that the stretching process caused significant exfoliation of the clay. These observations were based on an increase in mechanical properties, absence of clay peaks in XRD analysis and SEM images [14]. The reliance on XRD data and the lack of TEM images to support these observations can lead to erroneous conclusions being drawn regarding the state of exfoliation in a polymerclay composite as will be seen from the work presented in the current paper.…”