Polymer blends with polycaprolactone

Figure 5-6. (a) Dependence of T on p for mixtures of polymethyl methacrylate with diethyl phthalate. Comparison of experimental results with equation (5-8). Parameters found were ctjctp = 2.32, Tgd = -57 °C, Tgp = 104 °C.f [After F. N. Kelley and F. Bueche, J. Polym. Sci., 50 549 (1961)] (b) Variation of Tg for a miscible polymer blend of polycaprolactone (PCL) and poly(styrene-co-acrylonitrile) (SAN), with a description of the data using the Gordon-Taylor relationship, equation (5-27). The two points at low SAN content have a higher-than-expected Tg because of crystallization of the PCL. [After S-C. Chiu and T. G. Smith, J. Appl. Polym. Sci., 29,1797 (1984). Copyright 1984, Wiley Periodicals, Inc., a Wiley Company.]... 

The dependence of Tg on (f>P as predicted from equation (5-8) is plotted in Figure 5-6a for the system poly(methyl methacrylate)-diethyl phthalate, together with some experimental results. Tg can also be modified by blending with a miscible polymer component, which is widely practiced, particularly for PVC. A classical polymer blend comprising polycaprolactone (PCL) and poly(styrene-co-acrylonitrile) (SAN) is illustrated in Figure 5-6b. 

Yasin, M. and Tighe, B.J., Polymers for biodegradable medical devices. VIII. Hydroxybutyrate-hydroxyvalerate copolymers physical and degradative properties of blends with polycaprolactone. Biomaterials 13,9,1992. 

Polycaprolactone, which is widely used in medical applications, can be blended with a number of polymers such as styrene-acrylonitrile (SAN), PVC, and polycarbonate. In this example a polymer blend of polycaprolactone with a high nitrile SAN was expected to give a transparent extruded sheet which was thermoformable in hot water. Suitable thermoforming properties and adequate transparency had been achieved with 35 wt% polycaprolactone blended with 65 wt% SAN using small laboratory samples prepared in a torque rheometer. Unfortunately, strips extruded from a pellet blend using a 25 mm laboratory extruder were white, cloudy and not transparent. 

Other blends such as polyhydroxyalkanoates (PHA) with cellulose acetate (208), PHA with polycaprolactone (209), poly(lactic acid) with poly(ethylene glycol) (210), chitosan and cellulose (211), poly(lactic acid) with inorganic fillers (212), and PHA and aUphatic polyesters with inorganics (213) are receiving attention. The different blending compositions seem to be limited only by the number of polymers available and the compatibiUty of the components. The latter blends, with all natural or biodegradable components, appear to afford the best approach for future research as property balance and biodegradabihty is attempted. Starch and additives have been evaluated ia detail from the perspective of stmcture and compatibiUty with starch (214). 

Aliphatic polyesters based on monomers other than a-hydroxyalkanoic acids have also been developed and evaluated as drug delivery matrices. These include the polyhydroxybutyrate and polyhydroxy valerate homo- and copolymers developed by Imperial Chemical Industries (ICI) from a fermentation process and the polycaprolactones extensively studied by Pitt and Schindler (14,15). The homopolymers in these series of aliphatic polyesters are hydrophobic and crystalline in structure. Because of these properties, these polyesters normally have long degradation times in vivo of 1-2 years. However, the use of copolymers and in the case of polycaprolactone even polymer blends have led to materials with useful degradation times as a result of changes in the crystallinity and hydrophobicity of these polymers. An even larger family of polymers based upon hydroxyaliphatic acids has recently been prepared by bacteria fermentation processes, and it is anticipated that some of these materials may be evaluated for drug delivery as soon as they become commercially available. 

A wide range of thermoplastic starch compounds have been claimed in recent years. Formulations of thermoplastic starch with linear, biodegradable polyesters, including polycaprolactone and PHBV,174 176 and with polyamides175 have been reported. Laminated structures have been claimed using thermoplastic starch or starch blends as one or more of the layers.175,177,178 The use of polymers latexes as components of thermoplastic starch blends has also been claimed.179 181 Blends with natural polymers are also claimed, including cellulose esters182,183 and pectin.184 A crosslinked thermoplastic material of dialdehyde starch and protein has been reported.185... 

The most direct way of looking at the specific interactions is by using spectroscopic measurements. Infra-red spectroscopy is the technique which has been most commonly used to study mixtures involving polymers. Studies of blends of PVC with polycaprolactone showed shifts of 4-6 cm in the carbonyl band of polycapro-lactone relative to the pure polymer but this Figure should be treated with... 

Munk and co-woricers have been concerned with the above-stated problem for some time (38, 39). In this volume (40), their attention is focused on miscible blends of polycaprolactone and polyepichlorohydrin. These authors demonstrate that to a considerable degree the probe variation problem can be mitigated by scrupulous attention to experimental details in the IGC methodology. This concern for details is required at any rate, if the high data reproducibility needed for meaningful studies of interaction in miscible polymer blends is to be attained. These details center on modified methods for coating polymers onto solid supports, on improved methods for measuring carrier gas flow rates, and on enhanced, computer-based data analyses of elution traces. Also, corrections are made for contributions to retention times from uncoated support material. More than twenty volatile probes are used by Munk, and the probe-to-piobe variations in %23, while not entirely absent, are much less apparent than they would be under standard experimental protocols. 

The most direct way of looking at the specific interactions is by using spectroscopic measurements. Infra-red spectroscopy is the technique which has been most commonly used to study mixtures involving polymers. Studies of blends of PVC with polycaprolactone showed shifts of 4-6 cm 1 in the carbonyl band of polycapro-lactone relative to the pure polymer 99 l00), but this Figure should be treated with caution as the peak probably consists of the sum of a shifted and an unshifted peak and it is difficult to say what the frequency of the shifted peak would be, or what fraction of the carbonyl groups are, or can be, involved in the interaction. Frequency shifts have also been shown to exist in blends of poly(methyl methacrylate) with poly(vinylidene fluoride)63). 

The above mentioned scaffolds were made completely of the ceramic materials. Other potential materials which could be used to fabricate a novel construct for the repair of ciitical-sized bone defects is a novel material made of biodegradable polymer reinforced with ceramics particles. The properties of such a composite depend on 1) properties of the polymer used for the matrix and properties of the ceramics used for the reinforcement, 2) composition of the composite (i.e. content of ceramic particles) and 3) size, shape and arrangement of the particles in the matrix. Several polymer-composite composites have been used for scaffolds fabrication including polylactide (PLA) and polycaprolacton (PCL) reinforced with calcium phosphate (CaP) micro and nanoparticles. Authors proposed a novel composite material by blending copolymer -Poly(L-lactide-co-D,E-lactide) (PLDLLA) a copolymer with a ceramic - Tri-Calcium Phosphate... 

Endodontic points based on synthetic polymers are also available. One relatively new material is supplied as Resilon, manufactured by the Penton Clinical company, USA [15], and comprises a blend of polycaprolactone polymer with small amounts... 

Figure 4.25. (a) The mutual diffusion coefficient in the miscible polymer blend poly(vinyl chloride)-polycaprolactone (PVC-PCL) at 91 °C, as measured by x-ray microanalysis in the scanning electron microscope (Jones et al. 1986). The solid line is a fit assuming that the mutual diffusion coefficient is given by equation (4.4.11), with the composition dependence of the tracer diffusion coefficient of the PCL given by a combination of equations (4.4.9) and (4.4.10). The tracer diffusion coefficient of the PVC is assumed to be small in comparison, (b) The calculated profile of diffusion between pure PVC and pure PCL, on the basis of the concentration dependence of the mutual diffusion coefficient shown in (a). The reduced length u — where the... 

Due to the brittleness of starch materials, plasticizers are commonly used. A frequently utilized low weight hydroxyl compoxmd is glycerol. Another effective plasticizer is water, although not the best because it evaporates easily. Still, starch-based materials readily absorb water and this may result in significant changes in the mechanical properties. Different routes have been explored in order to improve the mechanical properties and water resistance of starch materials. These are chemical modifications to the starch molecule, blends with polymers such as polycaprolactone [61], or reinforcement with different types of cellulose-based fillers, such as ramie crystaUites [62], and timicin whiskers [63], or montmorillonite clay particles [64]. 

PHB and other PHAs can also be blended with other biodegradable polymers. In Japan, the Ministry of International Trade and Industry s Biological Industry Institute in 1990 announced the development of blends of PHB and polycaprolactone (PCL). The blends can be processed with conventional equipment, and the ratio of the two polymers determines the rate of degradation. ... 

J. A. Faucher and M. R. Rosen, Shaped Article for Conditioning Hair, a Blend of Water-Soluble and Water-Insoluble Polymers with Interpenetrating Networks, U.S. Pat. 4,018,729 (1977). Polymer blend, hair conditioning combs of (polycaprolactone blend, hair conditioning combs. Hair preparations, conditioners water insoluble/water soluble polymer blends and IPN-related materials. Combs and shaped articles. 

Ferreira et al. [75] synthesized a HMA for medical use. Urethanes based on polycaprolactone diol (PCL) were synthesized by reaction of the molecule either with isophorone diisocyanate (IPD-isocyanate) or hexamethylene diisocyanate (HDI-isocyanate). Nies Berthold et al. [76] tried out an adhesive composition based on polymers or polymer blends consisting of caprolactone copolymers or caprolactone copolymers and polycaprolactone. The adhesive can be utilized as HMA for temporarily gluing together biological tissue and other materials in medicine. 

The main applications are with PVC. The plasticizers which can be blended in can be either low MW organic compounds, e.g. dialkyl phthalates, phosphates (tricresyl phosphate which has flame-retardant characteristics) or low-MW polymers, e.g. polycaprolactone, PMMA, or copolymers of ethylene and vinylacetate (EVA). These are called external plasticizers. Internal plasticization can be achieved by copolymerizing VC with a comonomer which has a low Tg, e.g. vinyl acetate. 

The most common strategy to decrease the price or improve the properties of polylactide to fulfill the requirements of different applications is blending. Polylactide has been blended with degradable and inert polymers, natural and synthetic polymers, plasticizers, natural fibers and inorganic fillers. The most common blends include blends with other polyesters such as polycaprolactone or PLA/starch blends. Usually the compatibility between the two components has to be improved by addition of compatibilizers such as polylactide grafted with starch or acrylic acid (114,115). Recently a lot of focus was concentrated on the development of polylactide biocomposites, nanocomposites and stereocomplex materials. In addition various approaches have been evaluated for toughening of polylactide. 

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