Purity, polymers

The actual time required for poly-L-lactide implants to be completely absorbed is relatively long, and depends on polymer purity, processing conditions, implant site, and physical dimensions of the implant. For instance, 50—90 mg samples of radiolabeled poly-DL-lactide implanted in the abdominal walls of rats had an absorption time of 1.5 years with metaboHsm resulting primarily from respiratory excretion (24). In contrast, pure poly-L-lactide bone plates attached to sheep femora showed mechanical deterioration, but Httie evidence of significant mass loss even after four years (25). 

Bittner, B., Morlock, M., Koll, H., Winter, G., and Kissel,T. (1998), Recombinant human erythropoietin (rHEPO) loaded poly(lactide-co-glycolide) microspheres Influence of the encapsulation technique and polymer purity on microspheres characteristics, Eur. J. Pharm. Biopharm., 45, 295-305. 

Closed loop recycling materials from class 1 and class 4 can be considered to be safe and in compliance with the legal requirements due to the absence of contamination or the high purification effect of the de- and re-polymerisation steps. The materials from class 2 and 3 should have been sorted to a polymer purity of about 99%, which means also that materials from non-food packaging should also be separated. However, for the special case of PET, the FDA also allows non-food PET as an input material as long as the polymer is in compliance with 21 CFR 177.1630. 

Control of polymer purity and curability are the critical areas for future work. Some purity requirements will become quantified as this discussion proceeds. With regard to fiber cure, gas-phase chemical cure and energetic methods have been most effective to date 16,18). Fiber processing involving the dry spinning of thermally unstable polymers 4,11,19) may be of future importance, because the need for a separate cure step is eliminated. 

The discovery of poly(ethylene terephthalate), PET, in the 1940s [1,2] and its commercialization initially by DuPont and by ICI in the 1950s created a large market demand for terephthalic acid and terephthalate esters of polymer purity. Because dimethyl terephthalate, DMT, is readily purified by distillation [3] (and also because the p-xylene oxidation/esteiification intermediate, methyl p-toluate, is more readily kept in solution than is p-toluic acid) the polyester fibers and films industry was initially based on terephthalate ester. With the development of improved oxidation and purification technologies, purified terephthalic acid, TPA, became available in commercial quantities by the mid 1960s. Over 75% of the worldwide PET manufacture (total world PET capacity is over six million tons/year) is currently based on TPA rather than DMT [4]. This preference for TPA results from the less complicated esterification catalysis and the absence of methanol handling when the acid is used directly. 

Bittner B, Morlock M, Koll H, Winter G, Kissel T. Recombinant human erythropoietin (rhEPO) loaded polydactide-co-glycolide) microspheres influence of the encapsulation technique and polymer purity on microsphere characteristics. Eur J Pharm Biopharm 1998 45 295-305. 

H. Kokubo, T. Yamamoto, H. Kondo, Y. Akiyama and I. Fujimura. Purification of head-to-tail-type regioregular poly(3-hexylthiophene), HT-P3HexTh, and investigation of the effects of polymer purity on the performance of organic field-effect transistors. Jpn. J. Appl. Phys., Part 1 42(10), 6627-6628 (2003). 

From the above studies with purified and melt processed PL, one observes a much lower incidence of late stage foreign body reactions (1 in 227 patients or 0.4%) than with bulk-PL (13 in 39 patients or 33%) or with SRPL (5 in 152 or 3.3%). The role of polymer purity has been considered as a mitigating factor in at least one paper (Pihlajmaki et al, 1992). 

An exceptional advantage of self-reinforced thermoplastic composites is that they can be thermally recycled, but also reprocessed due to their polymer purity. This can be done by either returning the composite to a melted state or by simply re-granulating it. Thus, this process does without the complicated and expensive separation of the components, because an actual single-material system is on hand. Such a simple and useful recycling concept (in regard to material reuse) for the quantities currently in circulation has yet to be developed for the established foreign fiber reinforced thermoplastics. 

Coplymers used in this study were prepared by standard free radical polymerization in aqueous solutions. The NVP containing copolymers were prepared in high yield, using standard free radical initiation in aqueous solutions. The materials prepared were poly(AA-co-IA), poly(AA-co-NVP) and poly(AA-co-IA-co-NVP) (Tables I and II). The copolymers were easily isolated by standard freeze-drying techniques, with purification achieved by precipitation from diethyl ether, using concentrated methyl alcohol solutions of the polymers. Purity of the copolymers, i.e., absence of free monomers, was ascertained by thin layer chromatography. 

These new catalysts offer PO producers further steps in polymerization reactor outputs and improvements in polymer purity. Metallocene PP (mPP) is a cleaner, clearer, glossier polymer with a more uniform molecular size that could overcome the well known deficiencies of current isotactic PP (inadequate resilience and crush resistance, unsatisfactory dyeability, low sticking and softening temperature, processing difficulties to achieve maximum tensile strength, incompatibility of light stabilizers and flame retardant for PO fibers). 

Polymer—purity, molecular weight and molecular weight distribution, glass transition temperature (T ) or heat deflection temperature (HDT), and flow characteristics... 

The intrazeolite polymerization of aniline is believed to proceed in analogy to bulk chemical synthesis in n-hexane at 2 C initiated by (NH4)2S20s. It was found that different oxidation conditions for the intrazeolite polymerization of aniline allow one to control the level of polymer purity and level of intrazeolite acidity required for reaction. The intrazeolite polymers presented in this work are, according to the authors, a new family of molecular wires. 

The importance of polymer purity on the blood compatibility of P3HB and P3HB-3HV (4%, 18% 3HV) has recently been investigated. It has been... 

The processing of recyclates puts a high demand on the polymer purity. Numerous types of contaminants exist including solid particles of foreign matter (e.g., glass, paper, metal, paint, sand) and polymer particles. Separation of foreign particles is typically carried out by placing filters (also called... 

The experimental data are convincing that chemical structure of studied PAl lots is imperfect and polymer purity is poor. This makes processing more complicated and adversely affect the quality of marketable products, including material behavior during operation. 

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