Polymer blends optical microscopy

Tihe technological properties and the commercial application of several polymer blends have been studied extensively. Investigations of the basic principles, however, relating the phase structure of the blends to the properties of the individual components have not been carried out to an extent justified by the industrial value of these materials. Several methods have been used, the most successful being optical and electron microscopy and dynamic-mechanical measurements. Critical factors and difficulties in the morphological studies of polymer blends have been... 

Applications. Optical microscopy finds several important applications in filled systems, including observation of crystallization and formation of spherulites and phase morphology of polymer blends. " In the first case, important information can be obtained on the effect of filler on matrix crystallization. In polymer blends, fillers may affect phase separation or may be preferentially located in one phase, affecting many physical properties such as conductivity (both thermal and electrical) and mechanical performance. 

FIGURE 4.9 Apparent heat capacity and optical microscopy measurement (% light transmission) of a 75/25 poly(oxyethylene)/poly(ether sulfone) blend. (From Dreezen, G., Groen-inckx, G., Swier, S., and Van Mele, B., Polymer, 42, 1449, 2001. With permission.)... 

Figure 7. Morphologies of PP/PLA (40/60) polymer blend observed by (a) optical microscopy or (b) TEM and (c) PP/PLA/PP-g-PMMA (40/60/5) polymer...

Purely physical polymer blends are most commonly prepared by either mechanical mixing (melt) or dissolution in a common solvent followed by casting and solvent removal. In this study, both techniques were used the latter method was more readily applicable for film formation in small-scale laboratory batches. It was recognized that certain morphological differences between melt- and solution-fabricated polymers are often observed these include phase inversions and distortions, especially with graft and block polymers. However, casual observation by optical and electron microscopy revealed no dramatic differences between the melt- and solution-cast films, and this cannot be readily explained. 

In the first part of the chapter several methods used to observe morphology of polymer blends are presented. Various optical microscopic methods are reviewed, including such modem techniques as photon tunneling microscopy (PTM), scanning near-field optical microscopy (SNOM), phase measurement interference microscopy (PMIM), surface plasmon microscopy (SPM) and optical waveguide microscopy (OWM). Many of these methods have been developed to study surfaces and thin films. However, they can also be applied to polymer blend morphology. 

The polymers, whose characteristics are summarized in Table 1, were melt mixed in a Brabender-like apparatus at 200 C and at two residence times 6 min, at 2 r.p.m. and further 10 min. at 32 r.p.m. The blend compositions are listed in Table 2. After premixing, cylindrical specimens were obtained directly by extrusion using a melting-elastic miniextruder (CSI max mixing extruder mod. CS-194), Thermal and tensile mechanical tests were performed on these specimens by an Instron Machine (mod. 1122) at room temperature and at cross-head speed of 10 mm/min. Also made were morphological studies by optical microscopy of sections microtomed from tensile samples and scanning electron microscopy of fractured surfaces of samples broken at liquid nitrogen temperature. Further details on the experimental procedures and on the techniques used are reported elsewhere . 

Botana et al. [50] have prepared polymer nanocomposites, based on a bacterial biodegradable thermoplastic polyester, PHB and two commercial montmorillonites [MMT], unmodified and modified by melt-blending technique at 165°C. PHB/Na and PHB/ C30B were characterized by differential scanning calorimetry [DSC], polarized optical microscopy [POM], X-ray diffraction [XRD], transmission electron microscopy [TEM], mechanical properties, and burning behavior. Intercalation/exfoliation observed by TEM and XRD was more pronounced for PHB30B than PHB/Na,... 

Rameshwaram et al. [6] investigated the structure-property relationships and the effects of a viscosity ratio on the rheological properties of polymer blends using oscillatory and steady shear rheometry and optical microscopy. 

Sigillo et al. (1997) used several experimental methods for the measurement of interfacial tension of a model polymer blend. Common to all methods presented here are two main points. The first is that a is obtained from experiments where the shape of the interface between the liquids is directly observed by means of optical microscopy techniques. The second point is that the interface geometry is controlled by a balance between the interfacial force and the viscous stresses generated by some flow applied to the system. Measurements have been carried out on a model polymer blend, whose constituents are a polyisobutylene and a polydimethylsiloxane, both transparent and liquid at room temperature. When compared with each other, the values of interfacial tension obtained from the different methods show a good quantitative agreement. Excellent agreement is also found with results for the same system previously published in the literature. 

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