Microhardness blended polymers

Balta Calleja F J, Cagiao M E, Adhikari R and Michler G H (2004) Relating microhardness to morphology in styrene/butadiene block copolymer/polystyrene blends. Polymer 45 247-254. 

Nowadays, the microhardness technique, being an elegant, non-destructive sensitive and relatively simple method, enjoys wide application, as can be concluded from the publications on the topic that have appeared during just the last five years - they number more than 100, as is shown by a routine computer-aided literature search. In addition to some methodological contributions to the technique, the microhardness method has also been successfully used to gain a deeper understanding of the microhardness-structure correlation of polymers, copolymers, polymer blends and composites. A very attractive feature of this technique is that it can be used for the micromechanical characterization of some components, phases or morphological entities that are otherwise not accessible for direct determination of their microhardness. 

Bearing in mind the outlined peculiarities of condensation polymer blends, and particularly when they consist of one component and one phase (this case is more the exception rather than the general rule since block copolymers usually consist of two, three, or more phases), the application of the additivity law for the evaluation of their characteristics does not seem to be completely justified. The observed good agreement between the measured microhardness values and the calculated ones (Fig. 5.7) allows one to make an important conclusion in this respect. 

The study of the strain-induced polymorphic transitions by microhardness measurement offers the opportunity to gain additional information on the deformation behaviour of more complex polymer systems such as polymer blends. Since polymer blends are usually multicomponent and multiphase systems the question arises of how the independent components and phases react under the external load. The polymorphic transition will reflect the behaviour of the crystalline phases provided strain-induced polymorphic transition is possible. 

After following the microhardness behaviour during the stress-induced polymorphic transition of homo-PBT and its multiblock copolymers attention is now focused on the deformation behaviour of a blend of PBT and a PEE thermoplastic elastomer, the latter being a copolymer of PBT and PEO. This system is attractive not only because the two polymers have the same crystallizable component but also because the copolymer, being an elastomer, strongly affects the mechanical properties of the blend. It should be mentioned that these blends have been well characterized by differential scanning calorimetry, SAXS, dynamic mechanical thermal analysis and static mechanical measurements (Apostolov et al, 1994). 

In summarizing the results from the last three sections, one can conclude that the systematic variation of microhardness under strain performed on (a) homo-PBT (Section 6.2.1), (b) its multiblock copolymer PEE (Section 6.2.2) and (c) on blends of both of these (this section) is characterized by the ability of these systems to undergo a strain-induced polymorphic transition. The ability to accurately follow the strain-induced polymorphic transition even in complex systems such as polymer blends allows one also to draw conclusions about such basic phenomena as cocrystallization. In the present study of a PBT/PEE blend two distinct well separated (with respect to the deformation range) strain-induced polymorphic transitions arising from the two species of PBT crystallites are observed. From this observation it is concluded that (i) homo-PBT and the PBT segments from the PEE copolymer crystallize separately, i.e. no cocrystallization takes place, and (ii) the two types of crystallites are not subjected to the external load simultaneously but in a sequential manner. 

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. 

Mina, M. R, Ania, R, Balta Calleja R and Asano, T. 2004. Microhardness studies of PMMA/natural rubber blends. Journal of Applied Polymer Science 91(1) 205-210. 

Mina, M. R, Hague, M. E., Balta CaUeja, P. J., Asano, T., and Alam, M. M. 2004. Microhardness studies of the interphase boundary in rubber-softened glassy polymer blends prepared with/without compatibilizer. Journal of Macromolecular Science B Physics 43(5) 1005-1014. 

The use of the microhardness technique in blends of condensation polymers [PET/PEN and PET/polycarbonate (PC)] evidences the formation of copolymer sequences within the blends (30). 

Micromechanics of Polymer Blends Microhardness of Polymer Systems Containing a Soft Component and/or Phase... 

Microhardness on the interphase boundaries in polymer blends and composites and doubly injection molding processing... 

Using the repoited data on the experimentally derived values of glass transition temperature, Tg, degree of crystallinity, Vickers indentation microhardness, H, and blend compositions for homopolymers, block copolymers, blends of polyolefins, or of polycondensates, blends of miscible amorphous polymers and copolymers (some of them with rather complex molecular architecture), all of them containing a soft component and/or phase at room temperature, an attempt is undertaken to look for the reasons for the frequently reported drastic deviations of the experimentally derived H values from the calculated ones by means of the additivity law assuming that the contribution of the soft component and/or phase is negligibly small. 

Jungnickel B J (1996) Poly(vinylidene fluoride) (overview) in Polymeric Materials Encyclopedia, (Ed. Salamone J C) CRC Press, Boca Raton, Vol. 9, pp. 7115-7122. 37. Fakirov S, Balta Calleja F J and Boyanova M (2003) On the derivation of microhardness of amorphous blends of miscible polymers from glass transition temperature values, J Mater Sci Lett 22 1011-1013. 

Adhikari R, Michler G H, Cagiao M E and Balta Calleja F J (2003) Micromechaiiical studies of styrene/butadiene block copolymer blends, J Polym Eng 23 177-190. Michler G H, Balta Calleja F J, Puente I, Cagiao M E, Knoll K, Henning S and Adhikari R (2003) Microhardness of styrene/butadiene block copolymer systems Influence of molecular architecture, J Appl Polym Sci 90 1670-1677. 

Boneva D, Balt Calleja F J, Fakirov S, Apostolov A A and Krumova M (1998) Microhardness under strain 3. Microhardness behaviour during stress-induced polymorphic transition in blends of poly(butylene terephthalate) and its block copolymers, J Appl Polym Sci 69 2271-2276. 

---