In an inquiry regarding the original post, a reader stated:
All three methods of crosslinking are different. The original question was with regard to the effects of electron beam crosslinking on the melting point. In the case of e-beam, crosslinking takes place in the solid state. Due to...
In a recent e-mail inquiry, a reader asked:
In my experience, neither will occur.
First, the melting point is a function of crystalline packing --- the more uniform the packing, the higher the crystalline melting point of polyethylene. Melting point is not a function of molecular weight...
obrockmeier:
The long-term modulus will change with time due to creep or stress relaxation depending on whether you are holding the stress or the strain constant.
As a rule of thumb the modulus will change to 80% of the original modulus after 1 hour, 67% after 10 hours, 51% after 100 hours (4...
Ytse:
Unless your coating is 0.25 inches thick, the influence of the substrate will significantly affect the results of the test, as well as the radius of curvature of the test specimen.
The best way that I know of to take measurements on a pipe coating is the remove the coating from the pipe...
Vassia:
You’ve selected probably the two hardest materials to adhere either to each other or themselves. The only adhesive that I have found that works reasonably well is epoxy. It it’s best to oxidize the surfaces to be bonded by coarse-sanding followed by flame-treating to oxidize the...
In a recent e-mail, a subscriber posed the following question:
There is no magic wand that will make your life easy in regard to establishing your initial business plan. Your potential competitors are probably your best source of information on costs --- if you think one is willing to share...
Nigelt:
Please note that the parenthetical in the second paragraph in the previous post should read "lower initial strain", not "strain rate".
Rich Geoffroy
Polymer Services Group
polyserv@cox.net
Nigelt:
Stress can be a difficult concept with which to design. Stress is both time- and temperature-dependent. Not only is it difficult to assess the actual stress conditions of the part during service, but what does one use for failure stress --- deviation from the proportional limit...
Iboivin:
The best way to absolutely identify the difference between Neoprene (polychloroprene) and EPDM is by Infrared Spectrophotometry. Infrared analysis yields a “fingerprint” of the chemical composition of the polymer, and can easily differentiate between both polymers.
Most labs can...
AMWS:
In general, your supposition is correct, however polyethylene is something of a different animal. Remember, polyethylene has a low Tg (Glass Transition Temperature), somewhere around -60oC. Therefore, it should be a soft, gummy elastomer at room temperature. The reason it is a...
ajamnia:
Vicat and Heat Deflection Temperature are attempts to measure the deflection temperature of a polymer under load. These values are close to the Tg for amorphous polymers, but are generally no where near the Tg for a crystalline polymer, which generally exhibits a Tg well below room...
Clarification:
The second-order, or glass transition temperature, is also referred to as the “alpha”-transition, while a third-order transition is referred to as a “beta”-transition.
For those who may not remember, the first-order transition is the crystalline melting point for the polymer...
In an e-mail response to this thread, an Engineering-Tips reader wrote:
Oguzkesimci:
To my knowledge, polymers have only a single glass transition temperature. This second-order, or ?-transition is the temperature at which the mechanical behavior of the polymer changes from that of a...
Paul:
Dehydrochlorination, the evolution of HCl from PVC, is primarily the result of thermal degradation of PVC. Essentially heat and shear during processing causes hydrogen and chlorine from adjacent carbons to be liberated as HCl, leaving behind a carbon-carbon double bond. While the...
I take no credit for this article. I stumbled across it on Monster.com, and it was too appropriate to this forum to not pass this on.
Rich Geoffroy
Polymer Services Group
POLYSERV@aol.com
ResinBlend:
My first observation is that you’ve been bonding esters to esters (polyethylene terephthalate, ethylene-vinylacetate, ethylene-methylacrylate, and ethylene-ethyl acrylate) and now you’re attempting to bond an ester to an acid (ethylene-acrylic acid copolymer).
Try esterifying the...
First of all, the process will not make an epoxy, but it will make a PVC solvent cement. Secondly, why go through all that work when you can purchase it at any hardware store. The joint, however, will not be as strong as the PVC sheet itself. It will very likely break at the bond if you...
