Epoxies historical development

Disk thermistors can be produced to close limits of iaterchangeabihty, eg, 0.1 and 0.05° C. Disks cannot be made as small as the smallest beads 2 mm diameter seems an approximate practicable limit. Disks historically have been considered to be less stable than good beads. They are commonly protected with a coatkig of epoxy reski, which provides less compressive support than the glass coatkig of bead thermistors. More recent developments have resulted ki kiterchangeable glass-encapsulated disk thermistors which have the stabihty characteristics of the best beads. 

Historically, polymer-matrix composite materials such as boron-epoxy and graphite-epoxy first found favor in applications, followed by metal-matrix materials such as boron-aluminum. Ceramic-matrix and carbon-matrix materials are still under development at this writing, but carbon-matrix materials have been applied in the relatively limited areas of reentry vehicle nosetips, rocket nozzles, and the Space Shuttle since the early 1970s. 

Probably the first major publication of a process model for the autoclave curing process is one by Springer and Loos [14]. Their model is still the basis, in structure if not in detail, for many autoclave cure models. There is little information about results obtained by the use of this model only instructions on how to use it for trial and error cure cycle development. Lee [16], however, used a very similar model, modified to run on a personal computer, to do a parametric study on variables affecting the autoclave cure. A cure model developed by Pursley was used by Kays in parametric studies for thick graphite epoxy laminates [18]. Quantitative data on the reduction in cure cycle time obtained by Kays was not available, but he did achieve about a 25 percent reduction in cycle time for thick laminates based on historical experience. A model developed by Dave et al. [17] was used to do parametric studies and develop general rules for the prevention of voids in composites. Although the value of this sort of information is difficult to assess, especially without production trials, there is a potential impact on rejection rates. 

Hartmann and Lee [20] extended the types of calculations possible by using Ur to crosslinked polymers. They then developed [21] an alternative additive quantity (not favored by us, and presented here mainly for historical reasons) similar to UR, to calculate the shear modulus. Although the additive quantity for the shear modulus was initially developed [21] by using crosslinked epoxies as test cases, it is also useful for the much simpler uncrosslinked polymers. In the latest edition of his book, van Krevelen [7] provided tentative values for the group contributions to this new additive quantity, which he named the molar Hartmann function UH. Ujj has the same units as UR. Its value can be used in Equation 11.18 to estimate the shear... 

Historically, copper-clad laminates with acrylic or epoxy adhesives have been the major materials for flexible circuits. Each manufacturer has developed a special resin grade or special additives to ensure reliable flexibility and bond strength. Other adhesive materials such as phenol resin or silicon resin have been developed however, they have not become standard adhesive materials in flexible circuits. 

Epoxies have historically been the major adhesive family used for the structural bonding of metals and composites in the aerospace, industrial and automotive industries. They are characterised by curing to hard infusible resins that bond to a wide range of metals and have excellent resistance to heat and the environment. Epoxies have been used since the 1940s and have an excellent track record of successful structural bonding. Two-component and heat-cured one-component versions are available and literally thousands of formulations have been developed over the years for specific applications. 

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