Quote from: raven92 on July 30, 2012, 05:33 pmThis is interesting, although i've never heard of HDPP, I assume you meant HDPE? But if its HDPE you can't use HDPE's for hermetic sealing that i'm aware of, and I'd guess HDPP would just be referring to PP. I've seen people suggesting using mylar bags, which would make quite a bit of sense, even in the food communities Mylar is far superior for long term storage.Do you have more information on this or a link?Sorry for the delay. Here is the link and the quoted bits I think relevant to us.I was talking about polypropylene vs polyethylene, they are quite different.Macias, Michael S., "The Development of an Optimized System of Narcotic and Explosive Contraband Mimics for Calibration and Training of Biological Detectors" (2009). FIU Electronic Theses and Dissertations. Paper 123.http://digitalcommons.fiu.edu/etd/123Quote[Pine Note: The organization of the study into permeation rates]3.4.1. Controlled Odor Mimic Permeation System (COMPS)The chemical compounds used as odor mimic were prepared for presentation to caninesaccording to the physical appearance of the compounds. Solid compounds were weighedto various amounts and heat sealed within a polymer bags. Liquid compounds werespiked onto 2in x 2in sterile gauze pads and heat sealed within LDPE bags. The solidamounts varied from 5mg to 2g and liquid amounts varied from 1mL to 5mL. Thepolymer bags that were used included 3in x 3in 1.5mil, 2mil, 3mil, 4mil LDPE and 2milHDPP. The COMPS device was then heat sealed and stored within an aluminized Kapakbag. Negative controls were created by with blank media (i.e. blank gauze, emptypolymer bags, and blank tea candles).3.4.2. Permeation of Odor CompoundsOnce the COMPS were prepared, they were monitored (weighed) over the course oftwenty-one days to determine the mass loss per time, i.e. the permeation rate through thepolymer bags. At the conclusion of the weighing process, the data was plotted as mass vs.time. Each sample was made-up in triplicate for statistical purposes. The plotted resultsof average mass loss vs. time in days allowed for a calculation of permeation rate andhalf-life for each odor compounds through the polymer bags. Empty bags were also heatsealed and kept in the same environment to use as control samples. These controlswere made in triplicate blanks were kept and monitored concurrently to maintaina baseline.[Pine Note: On the two different types of plastic used in the study]Polymers:Polyethylene:Polyethylene is the most commonly encountered polymer used to date. Among its manycommercial uses include items such as grocery bags, shampoo bottles, children's toys,and even bullet proof vests. The simplest structure of all commercial polymers,polyethylene, is comprised of a long chain of carbon atoms with two hydrogen atomsattached to each carbon atom (Figure 11). The structure is referred to as a linearpolyethylene or high-density polyethylene (HDPE).Figure 11 - Polymer Structures [Pine Note: Look at the jpeg in the document]Within this simple structure, variations/mutations can occur. One mutation consists of thesubstitution of additional polyethylene chains in place of the hydrogens (Figure 12).Referred to as branching, the substitution occurs in low-density polyethylene (LDPE).LDPE has a lower tensile strength and higher ductility than HDPE. While linearpolyethylene offers a more rigid structure (i.e. it is much stronger), branchedpolyethylene is less expensive and easier to make than linear polyethylene.Polypropylene:Polypropylene is a versatile polymer that serves as both a plastic and as a fiber. As aplastic it is used to make things such as dishwasher-safe food containers. Polypropylenedoes not melt below 160oC, unlike polyethylene which anneals at 100oC causing dishes towarp in a dishwasher. As a fiber, polypropylene is used to make indoor-outdoorcarpeting. Because it is easy to color and resistant to water, it is often seen around poolsand miniature-golf courses.--[Pine Note: How they used the dogs as part of the study.]3.4.3. Field TrialsField trials were performed with trained and certified local law enforcement explosivedetection canine teams and drug detection canine teams. The odor aids were presented tothe canines in metal scent/electrical boxes, Sigma PseudoTM Scent Cages, or quart paintcans. Prior to use, the presentation vessels were cleaned with soap, rinsed with water, andplaced in an oven set to 110C for a minimum of 12 hours. After preparation, the odorsamples were presented to the canines in an odor line-up by placing the samples on thefloor approximately one meter apart (Figure 15). The handlers were instructed to workwith their detection canines to detail each sample in the line-up utilizing their normalsearch pattern. The handlers had no previous knowledge of the compounds or order ofplacement in the line-up. Additionally, there was no marking on the containers to indicatethe contents. A positive control and negative control were included in the odor line-ups.The positive control was an actual explosive sample provided by the police agency at thetime of testing. The negative control was an object from the ambient environment usedfor the trial. Forty-three certified drug detection canines and twenty certified explosive detectioncanines participated in this study. Field test attendance varied from three to ten canines atany given test. For data collection, analysis, and result reporting purposes, each caninewas assigned an individual three digit identification code. The code system also groupsthe canine teams into the explosive or drug detection category.[Pine Note: Finally the Paragraph that has us excited about HDPP's potential]:As expected, the permeation rate is affected by the thickness of the LDPE bags (Table15). The thinner the polymer bag, the faster the permeation rate (250ng/sec for 1.5milbag); conversely, the thicker the polymer bag, the slower the permeation rate (142ng/secfor 4mil bag). The low density form means that there is less organization to thepolyethylene structure because of branching (see section 2.5). This branching createsgaps, and the larger gaps, the easier it is for the compounds to pass through the polymer.Thicker polyethylene does not necessarily equate to a more structured form, but it doesprovide a thicker weave of polyethylene branches through which the compound mustpass. The increased time the compound spends passing though the polymer matrixreduces the permeation rate of the compound. Permeation through the HDPP bag wassubstantially lower than the thickest LDPE bags (19ng/sec vs. 142ng/s). The reduction inpermeation rate can be explained though the nature of a high density polymer and thepolypropylene structure. The rigidity of the isotactic blocks found in polypropylenecoupled with the high linearity characteristic of the high density form greatly reduces theavailable openings the compound to pass through resulting in a slower permeation rate.[Pine note: The Statistics]:Table 15 - Piperonal permeation rate values by bag thicknessBag Thickness (mil)Permeation Rate (ng/sec)1.5        250  102          208 63          173  184          142  4HD (2mil)      19  5Vendor Comment: Fuck yeah.Finally, they are extremely easy to obtain. Here is just one example of a website selling them:http://discountpolypropylenebags.co.uk/And why what a wonderfully informative site it is too!QuoteWhat are Polypropylene bags?Polypropylene poly bags are made from virgin polypropylene plastic. Polypropylene bags are versatile, attractive bags most commonly used for packaging small items such as beads and lollies. These bags can be sealed with a heat sealer like many other plastic bags. While polypropylene is similar to cello, polypropylene bags are much clearer with neater seals, and have the advantage of being less expensive than cello bags.Polypropylene poly bags have been the choice for product presentation and preserving freshness. Polypropylene poly bags are a high clarity crystal clear bag which enhances the product's image. They provide a highly protective barrier against moisture, dirt and vapors and meet FDA and EFSA specifications for food content. Polypropylene bags also referred as 'Polyprop bags' or 'PP bags'.These bags are by far the most popular for give away because of both its price and features. They are mainly used for displays. History of PolypropyleneProfessor Giulio Natta produced the first polypropylene resin in Spain in 1954. Natta utilised catalysts developed for the polyethylene industry and applied the technology to propylene gas. Commercial production began in 1957 and polypropylene usage has displayed strong growth from this date. The versatility of the polymer (the ability to adapt to a wide range of fabrication methods and applications) has sustained growth rates enabling PP to challenge the market share of a host of alternative materials in plethora of applications. [Pine Note: "plethora of applications" No fucking shit! :D :D :D]Properties of Polypropylene(Semi-rigid, translucent, good chemical resistance, tough, good fatigue resistance, integral hinge property, good heat resistance).Production of polypropylene takes place by slurry, solution or gas phase process, in which the propylene monomer is subjected to heat and pressure in the presence of a catalyst system. Polymerisation is achieved at relatively low temperature and pressure and the product yielded is translucent, but readily coloured. Differences in catalyst and production conditions can be used to alter the properties of the plastic.PP does not present stress-cracking problems and offers excellent electrical and chemical resistance at higher temperatures. While the properties of PP are similar to those of Polyethylene, there are specific differences. These include a lower density, higher softening point (PP doesn't melt below 160oC, Polyethylene, a more common plastic, will anneal at around 100oC) and higher rigidity and hardness. Additives are applied to all commercially produced polypropylene resins to protect the polymer during processing and to enhance end-use performance. [Pine Note: This is interesting too]CPP or cast polypropylene film is a multilayer polypropylene film with co-polymer and homo-polymer. It is used as a heat seal layer along with BOPP or polyester film in a laminate for packing of food articles. CPP films have been known in the packaging field to be the more elegant brother of polyethylene film, with higher gloss, greater transparency and better heat resistance. [Pine Note: I translate that to: certain types of HDPP should be the gold standard for long trips to hot places like Australia. Food Science you are unloved but we think you are the awesomest of all the sciences except maybe chemistry.]