Polycarbonate exposed

A maximum flexural stress of 9,500 psi is assumed for polycarbonate. This conservative stress value should account for degradation in ultraviolet stabilized polycarbonate exposed to long term solar exposure. While more research is required in this area, it is reasonable to expect at least a ten year useful life for ultraviolet stabilized polycarbonate. A Young s modulus of 345,000 psi and a Poisson s ratio of 0.38 are also assumed for polycarbonate. 

The importance of the UV absorber is illustrated by the following photomicrograph (Fig. 2) of uncoated and coated black pigmented polycarbonate exposed to 3 years of Arizona sun ... 

A. Krishna, E. Berg, Stress Cracking of Polycarbonate Exposed to Sunscreen (Delphi Automotive LLP, 2011-01-0037, 2011)... 

The interaction and relative role of the three mechanisms has not yet been explained, nor has the chemical structure of the compounds crucial for yellowing. Investigations of a non-stabilized polycarbonate, exposed to outdoor weathering in Florida for four years, indicate more than 40 different degradation products. The majority of these are degradation products caused by photo-oxidation, whereas... 

Fig. 4. Diagram of the two-step process to manufacture nucleation track membranes, (a) Polycarbonate film is exposed to charged particles in a nuclear reactor, (b) Tracks left by particles are preferentially etched into uniform cylindrical pores (8).

Track-etched membranes are made by exposing thin films (mica, polycarbonate, etc) to fission fragments from a radiation source. The high energy particles chemically alter material in their path. The material is then dissolved by suitable reagents, leaving nearly cylindrical holes (19). 

When fabricated polycarbonate parts are exposed to ultraviolet light, either in laboratory equipment or by outdoor exposure, a progressive dulling is observed on the exposed surface. The dullness is due to microscopic cracks on the surface of the resin. If the surface resin is analysed it is observed that it has a significantly lower molecular weight than the parent polymer. 

As previously mentioned, some urethanes can biodegrade easily by hydrolysis, while others are very resistant to hydrolysis. The purpose of this section is to provide some guidelines to aid the scientist in designing the desired hydrolytic stability of the urethane adhesive. For hydrolysis of a urethane to occur, water must diffuse into the bulk polymer, followed by hydrolysis of the weak link within the urethane adhesive. The two most common sites of attack are the urethane soft segment (polyol) and/or the urethane linkages. Urethanes made from PPG polyols, PTMEG, and poly(butadiene) polyols all have a backbone inherently resistant to hydrolysis. They are usually the first choice for adhesives that will be exposed to moisture. Polyester polyols and polycarbonates may be prone to hydrolytic attack, but this problem can be controlled to some degree by the proper choice of polyol. 

Many engineering thermoplastics (e.g., polysulfone, polycarbonate, etc.) have limited utility in applications that require exposure to chemical environments. Environmental stress cracking [13] occurs when a stressed polymer is exposed to solvents. Poly(aryl ether phenylquin-oxalines) [27] and poly(aryl ether benzoxazoles) [60] show poor resistance to environmental stress cracking in the presence of acetone, chloroform, etc. This is expected because these structures are amorphous, and there is no crystallinity or liquid crystalline type structure to give solvent resistance. Thus, these materials may have limited utility in processes or applications that require multiple solvent coatings or exposures, whereas acetylene terminated polyaryl ethers [13] exhibit excellent processability, high adhesive properties, and good resistance to hydraulic fluid. 

For on-site measurement from grab sampling, a compact optical device with disposable strips for BOD determination has been developed [36]. The system includes three pairs of light-emitting diodes and photodiodes, and the disposable strips are made of inexpensive, transparent polycarbonate plates, where Pseudomonas fluorescens is immobilized. Using the 2,6-dichlorophenol-indo-phenol sodium salt as chromophore, a linear relationship was observed between the bioluminescence of the exposed strip and the BOD value. 

A schematic of the INSIGHT screening tool is shown in Figure 4A. The INSIGHT screen consists of two polycarbonate or Teflon plates, each 12.7 mm thick (84). The top plate consists of a square matrix of 100 wells (each 3 mm in diameter). The bottom plate contains a symmetric matrix of 100 wells. The wells in the top plate act as the donors, and the wells in the bottom plate act as the receiver chambers in a FDC. Screening of formulations is performed using pigskin as a model. The skin is sandwiched between the donor and receiver plates. The SC is exposed to the test formulations in the donor. The receiver wells are filled with phosphate buffered... 

In environmental stress cracking the material fails by breaking when exposed to mechanical stress in the presence of organic liquids or wetting agents (soap solutions, etc.). A well-known example is the action of carbon tetrachloride in polycarbonate a little drop of this liquid on a strip of this polymer causes a very fast cracking upon a little bending of the strip. 

The following commercial polymeric substrates have been investigated low density polyethylene (PE, Dow Chemical Canada Inc.) polyimide (PI, DuPont Kapton H), polytetrafluoroethylene (PTFE, DuPont Teflon), polycarbonate (PC, Mobay Corp.) and surface-lubricated (with glycerol ester) polyvinylchloride (FVC, Canadian Occidental Petroleum Ltd). After plasma treatment, the samples were exposed to ambient atmosphere for 10 - 30 minutes while being transferred to the following... 

Figure 1 The absorption spectra of (4-(4-dimethylaminophenyl)-2,6-diphenyl-thia-pyrylium perchlorate) in dichoromethane, a homogeneous film of the perchlorate compound in bisphenol-A polycarbonate, and the aggregated dye produced by exposing the homogeneous film to dichloromethane vapors.

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