From balloon-request@cvs.rochester.edu Tue Aug 29 23:26:47 1995 id AA02134; Tue, 29 Aug 95 23:11:31 EDT Date: Tue, 29 Aug 1995 22:11:22 -0500 Message-Id: <199508300311.WAA212972@ux7.cso.uiuc.edu> To: balloon@cvs.rochester.edu From: Mark Balzer Subject: Re: more ?'s Tom writes: >This is good. I'm glad you think so, 'cuz I'm haven't been getting any schoolwork done lately... >Is vulcanization a fancy name for cooking? Yes and no. Here's an interesting history of rubber I just found in "Tinkers and Genius, the Story of the Yankee Inventors, by Edmund Fuller, Hastings House Publishers, NY, 1955." ..."India rubber"... Its original name was Caoutchouc (pronounced something like koochook). It was widely known as "gum elastic" but had come to be called "rubber" because its earliest recorded use (other than as balls to play with) by white men who fetched it from South America, was as an eraser. The "India" crept in as a joint reference to the South American Indians who gathered it and to the West Indies which became a trading channel for it. ...Around 1834... The India rubber trade was the next thing to being dead.... The plagued India rubber either melted and ran in the summer or petrified in the winter.... Scores of people were experimenting with the rubber problem.... As for Charles (Goodyear).... He recognized this as God's chosen work for him. Nothing would stop him.... The discovery of the sought-for secret came in 1839.... he was boiling rubber and sulphur on the kitchen stove, trying to make the curing process permeate it. A blob fell on the hot stove top and hardened. It was what came to be called "vulcanized." His work was not finished. How much sulphur? How much dry heat? How long for the process? These things had to be worked out experimentally. But Charles had it, he genuinely had it.... In success, he was at the extreme of bankruptcy.... For five years more he wandered in poverty around New England, working out the process, begging facilities, seeking a backer... It wasn't until 1844 that he got a patent. >Are there all levels of vulcanization from runny to hard? from "Chem One by Trublood, Waser and Knobler, McGraw-Hill, 1980" The vulcanization of rubber, by heating it with sulphur, which converts the rubber from a soft, gummy material into a product of varying hardness depending on the amount of sulphur used, involves the creation of cross-links that consist of -S-S- groups H H HCH H H | | | | THIS IS THE REPEATING UNIT IN ONE ... - C - C = C - C - ... POLYISOPRENE (NATURAL RUBBER) MOLECULE | | | H H H H H HCH H H | | | | ... - C - C - C - C - ... ONE POLYISOPRENE (NATURAL RUBBER) MOLECULE | | | | H H S H | VULCANIZED TO ANOTHER H S H H | | | | ... - C - C - C - C - ... POLYISOPRENE (NATURAL RUBBER) MOLECULE | | | | H H HCH H H (Polyisoprene is the major constituent of natural rubber) From "Introduction to Material Science for Engineers, Shackelford, MacMillan Publishing Co, NY, 1985" The extent of cross-linking is controlled by the amount of sulfur addition. This permits control of the rubber behavior from a gummy material to a tough, elastic one and finally, a hard, brittle product as the sulfur content is increased. Now Mark again: Oxygen is chemically very similar to sulfur, and can replace sulfur for cross-linking polyisoprene. They may take advantage of this fact in the balloon manufacturing process, or it may be what causes balloons to go bad from air exposure. I don't know for certain which - I'm a mechanical engineer, not a polymer chemist (though I play one on he net... :-) >Would not the amount of vulcanization make a great deal of difference >in the balance of the long force and the side force of a 260? No, the 2:1 balance of the hoop and axial stresses is a function of the pressure vessel (balloon) geometry, not the material. It's 2:1 for steel too. >There must be a best amount of vulcanization for a 260 to make the best >balance of forces for a 260. Well, there certainly must be a best amount of vulcanization for a 260 in order to make it best for twisting. It's probably determined by trial and error, then written down and kept in the company vault. >How would a 260 made from under cooked latex be different than a 260 that was >made from over cooked latex? The undercooked 260 would be red and bloody in the middle, and the overcooked 260 would taste smokey and burnt. >I wonder who is responsible for the cooking. Does Qualatex get the latex >pre-cooked? No. The "cooking" is done after the dipping. In the Qualatex-published book "Design" by Gary Wells, they state that: "Qualatex balloons are made from 100% latex. No fillers or substitutes are used." From "Introduction to Material Science for Engineers, Shackelford, MacMillan Publishing Co, NY, 1985" A filler is added to strengthen a polymer primarily by restricting chain mobility. ("chain" is short for "polymer chain" or molecule) It provides dimensional stability and reduced cost.... Roughly one third of the typical automotive tire is a filler (carbon black). "Design" also states: "Pioneer compounds its own latex and blends its own inks and dyes". From "Introduction to Material Science for Engineers, Shackelford, MacMillan Publishing Co, NY, 1985" Dyes are soluble organic colorants that can provide transparent colors... A pigment is an insoluble colored material added in powered form. monty writes: >What about the thermal properties of latex? I still don't have any idea >why small deviations in temperature have such a massive effect other than >perhaps the fact that it is derived from TREE SAP. Which of course as we >all know "flows" slower in cold. That was the only theory I had to explain >the slow-mo spread and large pieces that never contracted in my outside >clean-up. From "Introduction to Material Science for Engineers, Shackelford, MacMillan Publishing Co, NY, 1985" At relatively low temperatures, polymers are rigid solids and deform elastically (like spring steel). At relatively high temperatures, they are liquid-like and deform viscously (like cake batter).... The boundary between elastic and viscous behavior is known as the "glass transition temperature", Tg. For polymers, the modulus of elasticity (stiffness) is plotted (against Temperature). At low temperatures well below Tg, a rigid modulus (relatively constant, high stiffness) occurs, corresponding to mechanical behavior reminiscent of metals and ceramics. ^ | | : |_____: | :". | : ` : | : \ : S | r : } : T | i : { : I | g : ! : : F | i : ! : : F | d : l \ : : N | : e `.: : E | : a " - _ : S | : t : " ~ - _ : S | : h : " ~-. | : e : :` | : r : rubbery : \ | : y : : i | : : : | viscous | : : : +-----:----------:------------------------:--------> Tg Tm T E M P E R A T U R E In the glass transition temperature range, Tg, the modulus (stiffness) drops precipitously and the mechanical behavior is termed "leathery". The polymer can be extensively deformed and slowly returns to its original shape upon stress removal. Just above Tg, a "rubbery" plateau is observed. In this region, extensive deformation is possible with rapid spring back to the original shape when the stress is removed. (Latex is an "elastomer" - a polymer with a predominant rubbery region) As the melting point Tm is approached, the modulus (stiffness) again drops precipitously as we enter the liquid-like "viscous" region. Tom writes: >The exact level of vulcanization may be a most important part of making >a 260. >Tom Indeed. No doubt it's a crucial element of the total manufacturing process. >The old Ashland balloons had a rubbery feel and seemed to decompose faster >than the Qualatex. The feel of a balloon is tricky because there are >different finishes but I wonder if they started with a different level of >vulcanization. I expect that the exact process variables are proprietary trade secrets. This is schematically how vulcanizing affects the plot above (it raises the stiffness curve at all temperatures): ^ | | : |_____:_ | :".`. | : ` `. : | : \ `. : vulcanized curve S | r : } `.: / T | i : { `. / I | g : ! : " - _ / F | i : ! : " ~ - @ _ F | d : l \ : " ~ N | : e `.: E | : a " - _ S | : t : " ~ - _ : S | : h : " ~-. | : e : :` | : r : rubbery : \ | : y : : i | : : : | viscous | : : : +-----:----------:------------------------:--------> Tg Tm T E M P E R A T U R E Mark o _/ \_