Lamin monitoring

Key resins used in the manufacture of laminates are made with formaldehyde (qv). The A-stage resins are manufactured to have low levels of free formaldehyde, less than one percent, and plant atmospheres as well as individual operators are monitored to be certain they are exposed to levels of formaldehyde that are below OSHA guidelines of 0.75 ppm (14). 

It is appropriate at this juncture to illustrate the power of chemiluminescence in an analytical assay by comparing the limits of sensitivity of the fluorescence-based and the chemllumlnescence-based detection for analytes in a biological matrix. The quantitation of norepinephrine and dopamine in urine samples will serve as an illustrative example. Dopamine, norepinephrine, and 3,4-dihydroxybenzy-lamine (an internal standard) were derivatized with NDA/CN, and chemiluminescence was used to monitor the chromatography and determine a calibration curve (Figure 15). The limits of detection were determined to be less than 1 fmol injected. A typical chromatogram is shown in Figure 16. 

Mass spectrometers must be regularly tuned or calibrated against a known standard, e.g. perfluorotributy-lamine (PFTBA). The trend is towards miniaturisation (10 x 24 x 14 in.). A concept for a micro mass spectrometer, with potential applications in process monitoring, has been presented [167]. Mass-spectrometry instrumentation (1997) has been reviewed [166]. 

An easy way to evaluate the initiation rate, Y[ = Iq (1-e " 2,3 e l [pl]) Oj, and a possible deviation from its first-order dependence on the light intensity, is by monitoring the induction period (tj). Under air diffusion-free conditions (laminate), a given number of radicals (N) must be generated by photolysis of the initiator to consume the 02 molecules dissolved in the formulation, before polymerization can start ... 

With these solid supports in hand, we turned our attention to a new route to the synthesis of our target molecule 23 (Scheme 8). The tricky reductive amination should be replaced by an N-alkylation. To that end, bromoacetic acid is attached to 24c using DIC and Hiinig s base followed by the nucleophilic substitution with the corresponding benzy-lamine in DMSO/toluene (1 1), which can be easily monitored by the Beilstein test, followed by sulfonamide formation in DCM using N-methylmorpholine as base. For the final cleavage, 2% TFA in DCM is used and the resulting solution is filtered in a saturated NaHCC>3 solution to neutralise the acid before evaporation of the solvent. The crude product was then crystallised from ethyl acetate/heptane to yield the desired product in 27% yield overall and 99A% HPLC purity (see Table 4). 

Laminate expansion/contraction characteristics were determined with a DuPont Model 942 TMA. In this test the movement of an 0.38 cm diameter, hemispherical-tipped quartz probe resting on the specimen was monitored as the specimen was heated from room temperature through its softening range. 

Figure 11. Log (1/ct) vs. time for a thick graphite laminate (192 ply) catalyzed epoxy monitored during cure in the autoclave.

Tool-mounted optrode (TMO). The cure-monitoring experiments described here were conducted with a "tool-mounted" optrode (TMO) arrangement (5,6) (Figure 2) which is Ideally suited for the manufacturing environment where minimum interference with the laminate layup work is desirable. The use of a tool-mounted optrode is as simple as the use of tool-mounted thermocouples currently in wide use. Indeed, the TMO provides viscosity/degree-of-cure information on the cure state of the surface layer only. However, knowledge of the cure state of the surface layer permits determination of the cure states in the bulk based on the available models (1,2). 

In situ frequency dependent electromagnetic-impedence measurements provide a sensitive, convenient, automated technique to monitor the changes in macroscopic cure processing properties and the advancement of the reaction in situ in the fabrication tool. This chapter discusses the instrumentation, theory, and several applications of the techniques, including isothermal cure, complex time—temperature cure, resin film infusion, thick laminates, and smart, automated control of the cure process. 

Figure 6.12 Profiles of typical resin pressures monitored by the laminate, tool, and bleeder transducers. The profiles of time-temperature and the corresponding time—Pmjn for 35% and 85% initial relative humidity exposure of the prepreg—are also shown. (Source From [25])...

M 5] [P 4] Images of the distribution of a fluorescent species were monitored experimentally and calculated numerically within and behind the mixing section (1/6 Hz, 300 V for electroosmotic flow, 800 V to the electrodes) [92], Starting from an initial bi-laminating pattern, a transverse movement of the species is detectable and a homogeneous fluorescent texture is observed behind the mixing section. 

In-line concentration monitoring of multi-laminated streams... 

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