Blends PMMA/PVDF

Formally, the blend PMMA/PVDF can be considered as a three-phase one, because the reported density, p, values (Table 13.4, [34]) differ from the commonly accepted for p one. For the neat PVDF a density value of 1740 kg.m is reported [34], while in the literature a value for the fully amorphous PVDF (p J of 1680 kg.m can be found [14,36]. This difference in p suggests that some ordering in the system may have taken place during the sample preparation. Using the value of p = 1930 kg.m" for the completely crystalline PVDF [36] (which corresponds to the a-, also called type I-modification, i.e. crystallization from melt), one could estimate an appai ent degree of crystallinity = Pc /p[ P Pa) APc Pa)] Sample with p = 1740 kg.m", leading to Wf. = 0.25. 

Unlike most crystalline polymers, PVDF exhibits thermodynamic compatibiUty with other polymers (133). Blends of PVDF and poly(methyl methacrylate) (PMMA) are compatible over a wide range of blend composition (134,135). SoHd-state nmr studies showed that isotactic PMMA is more miscible with PVDF than atactic and syndiotactic PMMA (136). MiscibiUty of PVDF and poly(alkyl acrylates) depends on a specific interaction between PVDF and oxygen within the acrylate and the effect of this interaction is diminished as the hydrocarbon content of the ester is increased (137). Strong dipolar interactions are important to achieve miscibility with poly(vinyhdene fluoride) (138). PVDF blends are the object of many papers and patents specific blends of PVDF and acryflc copolymers have seen large commercial use. 

The kinetics of the crystallization process can be followed using the FT-IR technique 290). A particularly interesting example comes from the study of the polymer blends of PVDF/PMMA where the crystallization of the alpha and beta forms have been followed during heating of the blend samples which had been quenched from the melt and crystallized by heating at 2 °K/min in the spectrometer. Wien the blend has 70 wt % PVDF the beta crystal form is obtained directly but for other compositions the alpha form is dominant or unique. 

The homopolymers poly(methyl methacrylate) and poly-(ethyl methacrylate) are compatible with poly(vinylidene fluoride) when blended in the melt. True molecular com-patibility is indicated by their transparency and a single, intermediate glass transition temperature for the blends. The Tg results indicate plasticization of the glassy methacrylate polymers by amorphous poly(vinylidene fluoride). The Tg of PVdF is consistent with the variation of Tg with composition in both the PMMA-PVdF and PEMA-PVdF blends when Tg is plotted vs. volume fraction of each component. PEMA/PVdF blends are stable, amorphous systems up to at least 1 PVdF/I PEMA on a weight basis. PMMA/ blends are subject to crystallization of the PVdF component with more than 0.5 PVdF/1 PMMA by weight. This is an unexpected result. 

Physical Properties of PMMA—PVdF and PEMA—PVdF Poly blends. 

Tg data for the blends are shown in Figure 1. Results obtained by DTA on PMMA-PVdF blends which had been melt extruded and "annealed at room temperature appeared to be anomalous in terms of the theory for glass transition of copolymers or compatible polymer blends (6). These data indicated a limiting value for Tg of ca. 40°-45°C. However, x-ray examination showed that samples with more than ca, 35% PVdF exhibited a crystalline phase, indicating that some of the PVdF had precipitated. When these systems were re-examined by dilatometry... 

Figure 1. Glass transition temperature of PMMA-PVdF blends...

Figure 2. Comparison of experimental Tg values of PMMA-PVdF blends with theoretical curve based on Fox equation...

Thus, Tg should be a linear function of the volume fraction of each component rather than the weight fraction as implied by the Fox equation. When the Tg data are plotted vs. volume fraction, a reasonable fit is obtained for the PMMA-PVdF polyblends (Figure 3) and excellent agreement for PEMA-PVdF blends (Figure 4). [For these calculations,... 

Othfer properties of the PMMA-PVdF system are consistent with the amorphous-crystalline blend model. Thus, the light transmission of films of these blends at room temperature (Figure 5) decreases fairly abruptly as the the PVdF content increases, coincident with the appearance of a crystalline phase. 

Ultraviolet Stability of PMMA—PVdF Poly blends. The potential ultraviolet resistance of this polyblend was of considerable interest. Let us first consider what is known of the photochemical stability of the components. 

A. Flohr, 129Xe-NMR-spektroskopie und PVT-Untersuchungen am Blends von PVDF und PMMA, Duisburg 1995. [PhD Thesis]... 

For the system PMMA/PVDF one can estimate the volume of mixing according to Eq. (22). As the key-point, the system exhibits both LCST and UCST. The critical points are reported to be about at 325 and 140 °C for 50/50 blends [11], These data can be used to calculate, from Eqs. (18) and (19), the quantities XAB and p. 

Blends of PVDF and PMMA were studied by Tekely et al. [79] using MAS NMR, with cross polarisation from protons. They obtained data on PMMA magnetisation as a function of contact time for the... 

PMMA sufficiently close to the mixed phase that spin diffusion from it is important. Radial spin diffusion was assumed, with a sphere of intimately mixed phase of radius A and a shell of close PMMA of thickness L-A (up to a point of abutment with a neighbouring sphere). Figure 18.16 shows experimental data for the 60 40 PMMA/PVDF blend, which is fitted to A = 6 A, L = 12 A and 30% isolated PMMA. The same experiment was then employed [81], together with F- C H, F CP, to study the influence of PMMA tacticity on PMMA/PVDF miscibility, yielding evidence for a specific interaction between segments of the two polymers. The mixed PMMA/PVDF phase was determined to have a mean radius of 6-8 A, with some dependence on PMMA tacticity. Large differences were found in the... 

Fig. 18.15. CPMAS spectra of a PMMA/PVDF 60 40 blend (a) C direct CP (contact...

Amorphous polymers or regions of polymers can be regarded as micro-porous materials, and can be studied, therefore, by monitoring the Xe chemical shifts of adsorbed xenon gas. Mansfeld et al. [94] used this method to distinguish between incompatible blends (of polypropylene with a poly-propylene/polyethylene copolymer) and compatible blends (PMMA and PVDF). In the former case, two Xe signals were observed, whereas only... 

Fig. 18.16. Experimental data for a PMMA/PVDF 60 40 blend, obtained for the carboxyl resonance of PMMA. The solid line is a calculated depolarisation curve. The dashed line represents the offset from 30% of isolated PMMA. [Figure reproduced with permission from Ref. 80.]...

Fig. 18.17. Fraction of isolated PVDF in a 60 40 PMMA/PVDF blend as a function of annealing time at 120 and 140°C. [Figure reproduced with permission from Ref. 92.]...

The reader s attention is also drawn to two reviews [146,147] summarising the work of Veeman and Maas, discussed in Section 18.5, on PMMA/PVDF copolymers and blends. 

In this section, examples of films made from polyvinylidene fluoride (PVDF) are discussed. Although most of the pol5winylidene fluoride film is in the form of coating on metal substrates, stand-alone PVDF films and sheets are produced by extrusion and film blowing.1 ] ] Blends of PVDF and a number of other polymers such as polymethylmethacrylate (PMMA) are miscible. Films made from these blends have excellent piezoelectric properties. 

Note that nearly all commercial polymer blends (the exception is blend of PVDF with PMMA) are immiscible. One tends to study miscibility not to develop single-phase commercial blends, but mainly to design better compatibilizers and compatibilization strategies. 

PAr/ PVDF PAr-b- PMMA PVDF/PMMA is a miscible blend. Addition of PAr to the PAr/PVDF/PAr-b-PMMA resulted in reduction of PVDF T and an increase of PAr T. These effects were m g enhanced by addition of PAr-b-PMMA. Finer dispersion was obtained for higher block copolymer content. Contact angle measurements, showed that was greatly influenced by the presence of block copolymer. Ahn et al., 1994... 

It is well-known that the rate of crystallization of a crystalline polymer is often reduced by blending with a miscible amorphous polymer. Some typical examples are blends of PVDF/PMMA [Tanaka et al., 1985], PVDF/PEA [Alfonso and Russel, 1986], PEO/PMMA [Briber and lOioury, 1987] and PCL/SAN (19.2 wt% acrylonitrile) [ICressler et al., 1991]. 

Mishra et al. [1994] and Bajpai et al. [1994] determined the microhardness of PMMA/PVDF and PMMA/PCTFE blends (Table 11.9) made by solution casting from dimethyl formamide solutions. The solutions containing the two polymers were heated at 110°C for 3 h and were poured into an optically plain glass mold to prepare pellets of the blends. The poured material was annealed at 75°C for 3 h. The samples were cut from the slowly cooled (24 h) pellets for this work. 

Table 11.63. Microhardness of PMMA/PVDF blends [Mishra et al., 1994 Bajpai et at., 1994]...

The best commercial advantages of a polymer blend can be summarized by the word versatility [Olabisi et ah, 1979]. Unfortunately, miscible polymer-polymer blends usually show additivity of the component polymers properties, thus their versatility is limited. Furthermore, tike any other single-phase resin, for most apphcations miscible blends need to be toughened and/or reinforced. Thus, with the exception of PMMA/PVDF blends (primarily used for coatings) there are no miscible blends on the market The interest in miscible polymer blends is for the purpose of compatibUization and judicious selection of the processing conditions that may lead to the spinodal decomposition-type morphology (see Chapter 8 Morphology in this Handbook). 

Scanning electron micrographs (SEMs) of (a,b) polyaniline (PANI) network in 25/25/25/25 polystyrene/polymethyl methacrylate/poly(vinylidene fluoride)/polyaniline (PS/PMMA/ PVDF/PANI) blend after extraction of all phases by dimethylformamide (DMF) followed by freeze drying, and (c,d,e) PANI network in 15/20/15/25/25 PS/PS-co-PMMA/PMMA/PVDF/ PANI blend after extraction of all phases by DMF followed by freeze drying. (Reproduced from Ravati, S., and Favis, B. D. 2010. Low percolation threshold conductive device derived from a five-component polymer blend. Polymer 51 3669-3684 with permission from Elsevier.)... 

Conductive polyaniline (PANI) formed the core of the five-component continuous system that also included high-density polyethylene (HOPE), polystyrene (PS), poly(methyl methacrylate) (PMMA), and poly(vinylidene fluoride) (PVDF) along with PS-co-PMMA copolymer. Figure 1.10 shows the SEM micrographs of PANI network in PS/PMMA/PVDF/PANI and PS/PS-co-PMMA/PMMA/PVDF/PANI blends after extraction of all phases by DMF followed by freeze drying. 

PVDF/PMMA PVDF blends with PMMA and review of procedures used to determine X12 3... 

Blends of PVDF with PMMA have been studied by several authors. All three types of segregation were detected, which was attributed to variation of the crys-taUization temperature by Stein et al. (1981) and Morra and Stein (1982). Hahn et al. (1987) reported the existence of a compositional interphase (a region of varying polymer composition) between the lamellae and the amorphous interlayer. The order-disorder interphase seemed to contain pure PMMA, whUe in the remaining interlameUar region, a homogeneous mixture of PMMA and amorphous PVDF was located. 

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