Matrix, polymeric

Sihcon carbide fibers exhibit high temperature stabiUty and, therefore, find use as reinforcements in certain metal matrix composites (24). SiUcon fibers have also been considered for use with high temperature polymeric matrices, such as phenoHc resins, capable of operating at temperatures up to 300°C. Sihcon carbide fibers can be made in a number of ways, for example, by vapor deposition on carbon fibers. The fibers manufactured in this way have large diameters (up to 150 P-m), and relatively high Young s modulus and tensile strength, typically as much as 430 GPa (6.2 x 10 psi) and 3.5 GPa (507,500 psi), respectively (24,34) (see Refractory fibers). 

Energetic composites can be considered as particle-dispersed polymeric matrices. The mechanical properties of these systems are crucial to their dimensional and ballistic stability. Their ability to deform without rupture and to recover is important for successful performance. 

Incineration of a collection of polymers with 10 different kinds of brominated flame retardants has been studied under standardized laboratory conditions using varying parameters including temperature and air flow. Polybrominated diphenyl ethers like the deca-, octa-, and pentabromo compounds yield a mixture of brominated dibenzofurans while burning in polymeric matrices. Besides cyclization, debromination/hydrogenation is observed. Influence of matrix effects and burning conditions on product pattern has been studied the relevant mechanisms have been proposed and the toxicological relevance is discussed. 

The following 10 bromine compounds were investigated, in general within their polymeric matrices (see Scheme 1) ... 

For bromoethers 1-2 several other polymeric matrices were also used see below. Incinerations weie performed with the following three furnaces (Fig. 1-3) ... 

First, thermal behaviour of decabromobiphenyl ether 1 will be described. The thermal reactivity of this compound depends on the applied conditions the pure compound reacts completely different in comparison to its reaction in polymeric matrices. Thermolysis of the pure compound gives a good yield (60 %) of hexabromobenzene. The main products obtained by incineration in th DIN oven at three temperatures for pure 1 and of 1 within a polypropylene matrix are shown in Table 1. 

Besides these main products, formed in incineration of 1 in polymeric matrices complex isomeric mixtures of brominated methyl-dibenzofurans and brominated condensed systems like benzo[b]naphto[2,3-d]furan have been identified by GC/MS (ref. 11). 

Shih, C., Higuchi, T., and Himmelstein, K. J., Drug delivery from catalyzed erodible polymeric matrices of poly(ortho esters). Biomaterials. 5, 237-240, 1984. 

In comparison with hydrocarbon and polymeric matrices, which have their own absorptions in the IR and can react chemically with the intermediates, inert gas matrices are free of these shortcomings. Neon, krypton and xenon have been used as matrix substances in some studies. However, only argon and nitrogen matrices are widely adopted because of the availability of the pure gases and the fact that there is a variety of cryostats that can provide the optimal temperature conditions for the formation of rigid and transparent matrices from these elements. 

Principles and Characteristics A first step in additive analysis is the identification of the matrix. In this respect the objective for most polymer analyses for R D purposes is merely the definition of the most appropriate extraction conditions (solvent choice), whereas in rubber or coatings analysis usually the simultaneous characterisation of the polymeric components and the additives is at stake. In fact, one of the most basic tests to carry out on a rubber sample is to determine the base polymer. Figure 2.1 shows the broad variety of additive containing polymeric matrices. 

Extraction techniques for polymeric matrices can be divided into traditional and new . The traditional techniques include Soxhlet extraction, boiling under reflux, shaking extraction and sonication. All these methods are at atmospheric pressure. When the sample is added to a solvent, which is boiled under reflux (i.e. at the highest possible temperature without applying an external pressure) extractions tend to be much faster than Soxhlet extractions. Examples are the Soxtec ,... 

Successful extraction of additives from polymeric matrices requires a proper selection of organic solvents. Solvent choice was based on the following solvent properties ... 

MAE of additives from polymeric matrices has clearly established good records. Some additional studies may be needed in order to validate this approach for analytical sample preparation. Microwave heating has also been applied to dissolve polymers for molecular weight determination [446]. 

Work is in progress to validate the MAE method, proposed for EPA, in a multi-laboratory evaluation study. Nothing similar has been reported for additives in polymeric matrices. Dean el al. [452] have reviewed microwave-assisted solvent extraction in environmental organic analysis. Chee et al. [468] have reported MAE of phthalate esters (DMP, DEP, DAP, DBP, BBP, DEHP) from marine sediments. The focus to date has centred on extractions from solid samples. However, recent experience suggests that MAE may also be important for extractions from liquids. 

Experimental comparisons may suffer from a lack of optimal conditions for all methods considered or may be based on biased evaluation. It is frequently noticed that results quoted by the preferred extraction technique compare extremely favourably with existing extraction technology. Also, lack of prospects of using CRMs is not helpful for comparisons. However, it appears that for a given infrastructure (R D vs. plant laboratory) and need (routine vs. occasional operations), and depending on the mix of polymeric matrices to be handled, some preferences may clearly be expressed. 

On-line SFE-pSFC-FTIR was used to identify extractable components (additives and monomers) from a variety of nylons [392]. SFE-SFC-FID with 100% C02 and methanol-modified scC02 were used to quantitate the amount of residual caprolactam in a PA6/PA6.6 copolymer. Similarly, the more permeable PS showed various additives (Irganox 1076, phosphite AO, stearic acid - ex Zn-stearate - and mineral oil as a melt flow controller) and low-MW linear and cyclic oligomers in relatively mild SCF extraction conditions [392]. Also, antioxidants in PE have been analysed by means of coupling of SFE-SFC with IR detection [121]. Yang [393] has described SFE-SFC-FTIR for the analysis of polar compounds deposited on polymeric matrices, whereas Ikushima et al. [394] monitored the extraction of higher fatty acid esters. Despite the expectations, SFE-SFC-FTIR hyphenation in on-line additive analysis of polymers has not found widespread industrial use. While applications of SFC-FTIR and SFC-MS to the analysis of additives in polymeric matrices are not abundant, these techniques find wide application in the analysis of food and natural product components [395]. 

Table 8.1 shows some selected inorganic components in polymeric matrices. The broad variety of elements contained in polymers may be classified into three product-oriented categories ... 

It is concluded that MALDI-ToFMS is a suitable method for direct analysis of low-MW additives in complex polymeric materials (in dissolution), in particular as a rapid screening technique (within 0.5 h). However, in order to turn this method into a general tool for identification and quantitation, considerably more work needs to be done. Identification of additives in polymeric matrices by means of MALDI-ToFMS would greatly benefit from reference libraries of additives contained in such matrices. This is not unlike the situation observed for ToF-SIMS. 

Mass spectrometry combines exquisite sensitivity with a precision that often depends more on the uncertainties of sampling and sample preparation than on those of the method itself. Mass spectrometry is a supreme identification and recognition method in polymer/additive analysis through highly accurate masses and fragmentation patterns quantitation is its weakness. Direct mass spectrometry of complex polymeric matrices is feasible, yet not often pursued. Solid probe ToF-MS (DI-HRMS) is a breakthrough. Where used routinely, mass spectrometrists are usually still in charge. At the same time, however, costs need to be watched. 

Although the feasibility of direct probe MS for the analysis of additives in complex polymeric matrices has been demonstrated (Section 6.4), application is limited, difficult and requires above-average mass-spectroscopic expertise. Direct desorption in the MS probe is usually limited to screening of volatile components. Direct multicomponent spectroscopic analysis has other hurdles to overcome (UV/VIS lack of spectral discrimination IR/R functional-group recognition only, with no discriminative power for additives with similar functionalities NIRS unsuitable for R D problems NMR sensitivity). 

Quality assurance considerations lead to the need for appropriate reference materials, and their consistent and effective use to monitor the precision and accuracy of laboratory analyses. In this context, certified reference materials (CRMs), now still largely lacking in the polymer/additive area, play an important role. In previous years, some attempts have been undertaken to prepare some inorganic CRMs (VDA and PERM projects), but this is highly insufficient when we consider that some 60 elements are used in polymer/additive formulations. The lack of CRMs for organic compounds in polymeric matrices is an even more serious handicap. Nagoumey and Madan [122] have demonstrated that intermediate or finished in-house materials can be utilised successfully as QA reference materials. Good QC of polymer/additive formulations as yet has not been achieved. 

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