Crystallization and Thermal Properties

Poly(lactic acid) (PLA)-based products have been largely considered for both biomedical and environment-friendly applications [1-9]. Processing conditions and final properties of PLAs are strongly determined/influenced by the crystalline or amorphous structure of the polymer [10-12]. 

Starting from the early work of Kulkarni et al. [13, 14] in 1966 and 1971, many papers addressed the evaluation of thermal properties and crystallinity of PLA or polylactide-based polymers. 

The chiral nature of lactic acid results in distinct forms of polylactide, namely, poly(L-lactide) (PLLA), poly(D-lactide) (PDLA), and poly(DL-lactide) (PDLLA), which are synthesized from the L-, D-, and DL-lactic acid monomers, respectively, or from the corresponding L,L-lactide, D,D-lactide, and DL-lactide, respectively [15]. 

Both L- and o-lactic acid stereoisomers are naturally occurring however, most of the lactic acid in nature is L-type or sometimes racemic. The fact that lactic acid that is produced in the human body is in the L-enantiomeric form and the interest in the biomedical applications of this polymer have led both research and production to concentrate on L-lactide or OL-lactide polymers [16-18]. The o-isomer does not have many applications, except for use in particular medicinal chemicals. 

Today petrochemical-based production gives a 50/50 mixture of the l- and o-forms, whereas from fermentation mostly L-lactic acid is obtained. Recently, new research has been reported on the production of D-lactic acid from rice fermentation [19]. 

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Mechanical and Thermal Properties. The first member of the acrylate series, poly(methyl acrylate), has fltde or no tack at room temperature it is a tough, mbbery, and moderately hard polymer. Poly(ethyl acrylate) is more mbberflke, considerably softer, and more extensible. Poly(butyl acrylate) is softer stiU, and much tackier. This information is quantitatively summarized in Table 2 (41). In the alkyl acrylate series, the softness increases through n-octy acrylate. As the chain length is increased beyond n-octy side-chain crystallization occurs and the materials become brittle (42) poly( -hexadecyl acrylate) is hard and waxlike at room temperature but is soft and tacky above its softening point. 

Density, mechanical, and thermal properties are significantly affected by the degree of crystallinity. These properties can be used to experimentally estimate the percent crystallinity, although no measure is completely adequate (48). The crystalline density of PET can be calculated theoretically from the crystalline stmcture to be 1.455 g/cm. The density of amorphous PET is estimated to be 1.33 g/cm as determined experimentally using rapidly quenched polymer. Assuming the fiber is composed of only perfect crystals or amorphous material, the percent crystallinity can be estimated and correlated to other properties. 

A very high, price and performance family of polymers called liquid crystal polymers (LCPs) exhibit extremely high mechanical and thermal properties. As their ease of processing and price improve, they may find appHcation in thin-waH, high strength parts such as nails, bolts, and fasteners where metal parts cannot be used for reasons of conductivity, electromagnetic characteristics, or corrosion. 

Their special field of investigation dealt with the electrical and thermal properties of metals. More recently considerable attention has been paid to the question of the nature of the interatomic forces in metals, which are significant for properties such as density, compressibility, crystal energy, and hardness and it has been found possible to treat this problem in a reasonably satisfactory way for the case of the alkali metals, with a single valence electron per atom.8... 

There are several comprehensive textbooks and review articles devoted to organic superconductors [3,4,182-186] which describe design and preparation, crystal and band structures, chemical, transport, magnetic, optical, and thermal properties, and theory. 

A variety of surface-sensitive spectroscopic and microscopic methods were critical in the investigation of these systems. In the work by Advincula et al, the composition, thickness, physical and thermal properties, and morphology of the tethered polymer brushes were carefully analyzed [72]. A variety of surface-sensitive techniques such as ellipsometry, contact angle measurements, AFM, quartz crystal microbalance (QCM), FT-IR grazing incidence... 

Leibfrid G., 1963, Mikroskopocheskaya teoriya mekhanicheskikh i teplovykh svoistv kristallov (Microscopic Theory of Mechanical and Thermal Properties of Crystals), Fizmatizdat, Moskva. 

A.H. Deutchman and R.J. Partyka (Beam Alloy Corporation observe, "Characterization and classification of thin diamond films depend both on advanced surface-analysis techniques capable of analyzing elemental composition and microstructure (morphology and crystallinity), and on measurement of macroscopic mechanical, electrical, optical and thermal properties. Because diamond films are very thin (I to 2 micrometers or less) and grain and crystal sizes are very small, scanning electron microscopy... 

The electrical, mechanical, and thermal properties of the crystal are then largely determined by the electrons in the energy levels within the highest occupied bands. 

He, G.-X. Wada, F. Kikukawa, K. Shinkai, S. Matsuda, T., (1990) Syntheses and thermal properties of new liquid crystals bearing a crown ether ring cation binding in the nematic phase J. Org. Chem. 55, 541-548. 

In the absence of good quality single crystal samples, the physical properties of indium nitride have been measured on non-ideal thin films, typically ordered polycrystalline material with crystallites in the 50 nm to 500 nm range. Structural, mechanical and thermal properties have only been reported for epitaxial films on non-lattice-matched substrates. 

Lopez, C., Lesieur, P., Keller, G., Ollivon, M. 2001a. Crystallization in emulsion application to thermal and structural behaviour of milk fat. In, Crystallization and Solidification Properties of Lipids (N. Widlak, R. Hartel, S. Narine, eds.), pp. 190-199, AOCS Press, Champaign, IL. 

Fujiwara T, Yamazaki M, Tbmiza Y, Ibkuoka R, Tomita K-I, Matsuo T, Suga H, Saenger W (1983) The crystal structure of a new form of yS-cyclodextrin water inclusion compound and thermal properties of /teyclodextrin inclusion complexes. Nippon Kagaku Kaishi 2 181-187... 

SYNTHESIS AND THERMAL PROPERTIES OF IONIC PLASTIC CRYSTAL ELECTROLYTES... 

In this chapter, we present results of the testing of a broad spectrum of polymers in carbon dioxide over a range of temperatures and pressures and evaluation of the effect of the high pressure carbon dioxide on the chemical/physical properties of materials tested. The testing was performed in a static manner with four controlled variables, namely temperature, pressure, treatment time and decompression time. The evaluation of the interaction of high pressure carbon dioxide with polymers included sorption and swelling behavior, solubility issue, plasticization and crystallization, and mechanical properties. The results of these evaluations are discussed in three sections Sorption, Swelling and Dissolution of Carbon Dioxide in Polymers at Elevated Pressure, Thermal Properties, and Mechanical Properties. ... 

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