Miscibility and Crystallization

Blends of HOPE with long-chain branched polyethylenes (HBPE) prepared from metallocene catalysts have been studied by DSC and their crystal stmcmres interpreted in terms of phase behavior. The HBPE contained long-chain branches and short branches formed form octane comonomer. HBPE with 7.5-12.0% octane exhibited phase separation, whereas HBPE with 2% octane were found to be miscible with HOPE over the whole composition range. Eong branches were few and did not contribute to the immiscibility (16). 

Crystallization and melting of ternary blends containing mPE, EEDPE, and EDPE have been studied where the mPE and EEDPE varied in content and had the same melting temperature, TE = 122°C and a fixed content of EDPE, Tin = 114°C. Crystallinity increased with mPE content, and it was proposed that mixed crystals may be formed since no separated melting peaks were observed for the component PE (17). Blends of EPE and several different poly(ethylene-cohexene)s were shown. 

Phase diagrams have been proposed for blends of polyethylenes where the first component is linear, or less branched, and the second component is more branched. The method involves quench cooling each blend composition from the melt at various temperatures, so that there is insufficient time for liquid-liquid phase separation. Separated blends are considered to be separated at the particular temperature of the melt prior to quenching. TEM and DSC are used to characterize the quenched blends. The phase diagrams exhibit UCST behavior, depending on the difference in branching content of the component polyethylenes. Branch length has been found not to be important since it is the branch points that are excluded from the crystals (20,21). 

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There have been many related works by other research groups that are concerned with the phase behavior, isothermal crystallization kinetics, and tensile properties of cellulose propionate (DS = 2.75)/PHB blends [129], the miscibility and crystallization behavior of CAB/PHB blends [ 130], or the melt... 

Miscibility and Crystallization Behavior in Binary Polyethylene Blends... 

These PE polymers offer a broad spectrum of structures, properties, and applications. However, the blending of different types of PEs (HDPE, LDPE, LLDPE, and UHMWPE) has attracted growing interest because of the potential for obtaining low cost materials with improved mechanical properties and better processabilities, as compared to those of the pure constituents (1-34). Nowadays, 70% of PEs in the market are blends (24). The processability and properties of PE blends are dependent on the melt miscibility. Moreover, the properties are also dependent on the morphological structure of the blend, which is basically a combination of the crystallization behavior and melt miscibility. Therefore, the miscibility and crystallization behavior of PE blends have been prevalent research topics over the last two decades. 

The miscibility and crystallization behavior of the three binary PE blends, HDPE/ LLDPE, HDPE/LDPE, and LLDPE/LDPE, were reviewed. In general, differences in the number, length, and distribution of branches in the PE blend components are the major factors governing their miscibility and crystallization phenomenon. In particular, the content and distribution of branches significantly affect both the miscibility and crystallization. Moreover, the presence of a few long chain branches, as well as... 

It is noted, however, that studies on both the miscibility and crystallization behavior of PE blends are quite limited due to experimental difficulties, in particular those caused by the chemical repeat units of linear and branched PEs having the same molecular nature. Therefore, the development of more quantitative analytical techniques is still needed in order to fully understand the miscibility and crystallization behavior of PE blends. 

X. Kong, F. Teng, H. Tang, L. Dong, and Z. Feng. Miscibility and crystallization behaviour of poly(ether ether ketone)/polyimide blends. Polymer, 37(9) 1751-1755, April 1996. 

Chen C, Dong L, Yu PHE (2006) Characterization and properties of biodegradable poly(hydroxyalkanoates) and 4,4-dihydroxydiphenylpropane blends intermolecu-lar hydrogen bonds, miscibility and crystallization. Eur Polym J. doi 10.1016/j.eurpol ymj.2006.1007.1005... 

Qiu, Z., Ikehaia, T. and NisM, T. (2003) Miscibility and crystallization behaviour of biodegradable blends of two atiphatic polyesters. Poly(3-hydroxybutyiate-co-hydroxyvalerate) and poly(butylene succinate) blends. Polymer, 44 (24), 7519 7527. 

Longitudinal polymer liquid crystal + engineering polymer blends miscibility and crystallization phenomena... 

Miscibility and crystallization behavior of poly(L-lactide)/poly(p-vinylphenol) blends. Polymer, 39, 4841 847. 

Xing, P., Dong, L., An, Y, Feng, Z., Avella, M., and Martuscelli, E. (1997) Miscibility and crystallization of poly (P-hydroxybutyrate) and poly(p-vinylphenol) blends. Macromolecules, i0272G-27ii. 

Qiu Z, Ikehara T, Nishi T. Miscibility and crystallization in crystalline/crystalline blends of poly(butylene succi-nate)/poly(ethylene oxide). Polymer 2003 44 2799-2806. 

Simon GP. Longitudinal polymer liquid crystal+engineering polymer blends miscibility and crystallization phenomena. In Brostow W, editor. Mechanical and thermophysical properties of polymer liquid crystals. London Chapman and Hall 1998. p. 172-213. [Chapter 7]. 

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