{"id":9055,"date":"2026-11-05T01:00:00","date_gmt":"2026-11-05T01:00:00","guid":{"rendered":"https:\/\/uplastech.com\/?p=9055"},"modified":"2026-11-05T01:00:00","modified_gmt":"2026-11-05T01:00:00","slug":"silicone-outgassing","status":"publish","type":"post","link":"https:\/\/uplastech.com\/it\/silicone-outgassing\/","title":{"rendered":"Silicone Outgassing: Why Sealed Enclosures Fog Up"},"content":{"rendered":"<style>\n.upl-blog{font-size:17px;line-height:1.78;color:#1f2937}\n.upl-blog p{margin:0 0 18px}\n.upl-blog h2{font-size:26px;line-height:1.3;color:#0b2b33;margin:46px 0 14px;font-weight:700;letter-spacing:-.015em}\n.upl-blog h3{font-size:19.5px;color:#0d3b47;margin:28px 0 10px;font-weight:700}\n.upl-blog ul,.upl-blog ol{margin:0 0 20px;padding-left:22px}\n.upl-blog li{margin:0 0 9px}\n.upl-blog figure{margin:0 0 34px}\n.upl-blog figure img{width:100%;height:auto;display:block;border-radius:10px}\n.upl-blog figcaption{font-size:13px;color:#6b7280;margin-top:10px;line-height:1.5}\n.upl-blog .toc{background:none;border:0;border-radius:0;padding:0;margin:0 0 34px}\n.upl-blog .toc .lwptoc{margin:0}\n.upl-blog .toc h4{margin:0 0 10px;font-size:13px;letter-spacing:.1em;text-transform:uppercase;color:#0d5563}\n.upl-blog .toc ol{margin:0;padding-left:18px;font-size:14.5px}\n.upl-blog .toc li{margin-bottom:6px}\n.upl-blog table{width:100%;border-collapse:collapse;font-size:14.5px;margin:0 0 10px}\n.upl-blog th{background:#0d3b47;color:#fff;text-align:left;padding:11px 13px;font-weight:600;font-size:13.5px;border:0}\n.upl-blog td{padding:11px 13px;border:0;border-bottom:1px solid #e8ebed;vertical-align:top}\n.upl-blog tbody tr:nth-child(even){background:#fafbfc}\n.upl-blog .tablecap{font-size:12.5px;color:#6b7280;margin:0 0 30px}\n.upl-blog .myth{background:#fff8ef;border:1px solid #f6ddbd;border-radius:8px;padding:16px 20px;margin:0 0 26px;font-size:15.5px}\n.upl-blog .myth b{color:#a85c10}\n.upl-blog .callout{background:#f2f8f9;border-radius:8px;padding:18px 22px;margin:0 0 26px;font-size:15.5px;border-left:3px solid #14707f}\n.upl-blog .faq h3{border-top:1px solid #eceff1;padding-top:22px;margin-top:0;font-size:18px}\n.upl-blog .faq h3:first-of-type{border-top:0;padding-top:0}\n.upl-blog .cta{background:linear-gradient(135deg,#0b2b33,#0d5563);color:#fff;border-radius:12px;padding:34px;margin:48px 0 30px}\n.upl-blog .cta h2,.upl-blog .cta .cta-h{color:#fff;margin:0 0 10px;font-size:24px;font-weight:700;line-height:1.3}\n.upl-blog .cta p{color:#c9dee3;margin:0 0 20px;font-size:16px}\n.upl-blog .btn{display:inline-block;background:#e07a1f;color:#fff;text-decoration:none;font-weight:700;padding:13px 26px;border-radius:8px;font-size:15.5px}\n.upl-blog .rel{border-top:1px solid #e8ebed;margin-top:40px;padding-top:26px}\n.upl-blog .rel h4{font-size:13px;letter-spacing:.1em;text-transform:uppercase;color:#6b7280;margin:0 0 14px}\n.upl-blog .rel ul{list-style:none;padding:0;margin:0}\n.upl-blog .rel li{padding:11px 0;border-bottom:1px dashed #e8ebed}\n.upl-blog .rel a{text-decoration:none;font-weight:600;font-size:15.5px}\n@media(max-width:640px){.upl-blog h2{font-size:22px}.upl-blog table{font-size:13px}.upl-blog .cta{padding:24px}}\n\/* \u5355\u7bc7\u9875\u9690\u85cf WhatsApp \u95ee\u5019\u5361\uff0c\u53ea\u4fdd\u7559\u5706\u5f62\u6c14\u6ce1\uff0c\u907f\u514d\u906e\u6321\u4fa7\u680f\u8be2\u76d8\u63d0\u4ea4\u6309\u94ae\u3002\n   \u6ce8\u610f\uff1aClick to Chat \u7684\u70b9\u51fb\u903b\u8f91\u662f\u300c\u95ee\u5019\u5361\u5143\u7d20\u5b58\u5728\u5c31\u4e0d\u8df3\u8f6c\u300d\uff0c\u53ea\u9760 CSS \u9690\u85cf\u4f1a\u8ba9\u6c14\u6ce1\u53d8\u6210\u6b7b\u94fe\u63a5\u3002\n   Code Snippets #9\u300cUPL single post: WhatsApp bubble jumps straight to chat\u300d\u8d1f\u8d23\u628a\u8be5\u8282\u70b9\u4ece DOM \u79fb\u9664\uff0c\n   \u4e0b\u9762\u8fd9\u6761 CSS \u53ea\u662f\u79fb\u9664\u524d\u7684\u89c6\u89c9\u515c\u5e95\u3002\u5220 #9 \u524d\u5fc5\u987b\u5148\u5220\u8fd9\u6761\u89c4\u5219\u3002 *\/\nbody.single-post .ht_ctc_chat_greetings_box{display:none !important}\n<\/style>\n<div class=\"upl-blog\">\n<figure>\n<img fetchpriority=\"high\" decoding=\"async\" src=\"https:\/\/uplastech.com\/wp-content\/uploads\/2026\/10\/sr-05-silicone-gaskets.jpg\" alt=\"White and black silicone O-rings and gaskets laid out on a bench\" width=\"1536\" height=\"909\"><figcaption>A gasket that never degrades can still fill a sealed box with volatiles.<\/figcaption><\/figure>\n<div class=\"toc\"><\/div>\n<h2 id=\"what\">What silicone actually releases<\/h2>\n<p>Outgassing is the release of volatile molecules from a material over time, driven by heat and by vacuum. In silicone rubber the volatiles are mostly low molecular weight siloxanes that were never bound into the network.<\/p>\n<p>Curing links most of the polymer into a cross linked network, but a fraction stays as free chains and cyclic species. Cyclic siloxanes, especially D4, D5 and D6, are the classic offenders because they are volatile and chemically inert.<\/p>\n<p>There is also water and, in condensation cure systems, the small molecule released by the cure reaction itself. Peroxide cure leaves decomposition products behind unless a post cure drives them off.<\/p>\n<p>None of these make the rubber defective. A fully cured silicone gasket can still emit enough to haze a lens, and that is the surprise that catches design engineers.<\/p>\n<h2 id=\"where\">Where outgassing bites<\/h2>\n<p>Sealed enclosures are the worst case. Volatiles have nowhere to go, so they accumulate until they condense on the coolest surface, which is usually the window or the lens.<\/p>\n<p>Optical assemblies see it as haze or a film that appears over weeks. Electronics see it as contact contamination and, in high humidity, as leakage across a surface.<\/p>\n<p>Automotive sensors see it as drift, because a film on the sensing element changes its response. Space and vacuum applications see it as mass loss and as condensate on cold optics, which is why ASTM E595 exists.<\/p>\n<p>Medical devices see it as extractables. A volatile that is harmless in air becomes a leachable when the part is in contact with fluid, and the test moves from outgassing to extraction.<\/p>\n<h2 id=\"measure\">How it is measured<\/h2>\n<p>ASTM E595 heats a sample to 125 degrees Celsius under vacuum for 24 hours and measures two numbers: total mass loss, TML, and collected volatile condensable materials, CVCM, which is what actually deposits on a cold surface.<\/p>\n<p>CVCM is the number that matters for optics and sensors. A material can lose a lot of mass as water and still have a low CVCM, because water does not condense on a warm window.<\/p>\n<p>For general industrial work, thermogravimetric analysis or a simple mass loss test at the service temperature is enough. It will not give a space grade number but it ranks materials correctly.<\/p>\n<p>Gas chromatography tells you what the volatiles are. That matters when the failure is specific, for example when a customer's adhesive is attacked by a particular siloxane rather than by silicone in general.<\/p>\n<h2 id=\"postcure\">Post-cure is the main lever<\/h2>\n<p>Post-curing drives off the volatiles before the part goes into service. Hold the part above its service temperature for a few hours and most of what would have outgassed in the field leaves in the oven instead.<\/p>\n<p>The left chart is mass loss against post-cure time at 200 degrees for a platinum cured liquid silicone. Four hours takes it from 1.8 percent to 0.45; sixteen hours takes it to 0.3.<\/p>\n<p>The curve flattens. Doubling from sixteen to forty-eight hours buys only a little more, which is why most specifications settle on a practical post-cure rather than an indefinite one.<\/p>\n<p>Temperature matters more than time. A post cure at 200 degrees removes in four hours what a post cure at 150 degrees needs all day to achieve, because diffusion through the rubber is strongly temperature dependent.<\/p>\n<figure>\n<img decoding=\"async\" src=\"https:\/\/uplastech.com\/wp-content\/uploads\/2026\/11\/silicone-outgassing-chart.jpg\" alt=\"Mass loss falling with post-cure time, and CVCM for different silicone grades\" width=\"1536\" height=\"909\"><figcaption>The first four hours do most of the work.<\/figcaption><\/figure>\n<h2 id=\"grades\">Grades and cure chemistry<\/h2>\n<p>The right hand panel compares CVCM by grade. Peroxide cured rubber is the highest at 0.45 percent because the cure itself leaves fragments behind; standard platinum is lower at 0.30.<\/p>\n<p>A post-cured platinum part reaches 0.12, and a purpose-made low outgassing grade reaches 0.05. The last step is a formulation choice, usually a stripped polymer with the light ends removed before compounding.<\/p>\n<p>So there are three levers, in order of cost: post-cure, which costs oven time; cure chemistry, which costs a different compound; and a low outgassing grade, which costs more per kilogram.<\/p>\n<p>Most applications are solved by the first lever alone. Reaching for an exotic grade before post-curing properly is paying for a problem you did not have.<\/p>\n<h2 id=\"specify\">Specifying for a sealed assembly<\/h2>\n<p>State the service temperature and whether the enclosure is sealed. Those two facts decide whether outgassing matters at all, and they are the two most often left off a drawing.<\/p>\n<p>If it matters, specify CVCM rather than TML, and specify the test. A limit of 0.1 percent CVCM to ASTM E595 is meaningful; 'low outgassing' is not.<\/p>\n<p>Ask for the post-cure to be recorded. A supplier who post-cures to schedule will show it on the certificate, and a supplier who does not will show nothing, which is the answer.<\/p>\n<p>And design an escape route. A vent, a desiccant or a breathable membrane turns a sealed box into a managed one, and often costs less than qualifying a new compound.<\/p>\n<table>\n<thead>\n<tr>\n<th>Volatile<\/th>\n<th>Fonte<\/th>\n<th>Effect<\/th>\n<\/tr>\n<\/thead>\n<tbody>\n<tr>\n<td>D4 \/ D5 \/ D6<\/td>\n<td>Free cyclic siloxanes<\/td>\n<td>Fogs optics, contact films<\/td>\n<\/tr>\n<tr>\n<td>Water<\/td>\n<td>Absorbed moisture<\/td>\n<td>Low CVCM, high TML<\/td>\n<\/tr>\n<tr>\n<td>Cure byproduct<\/td>\n<td>Condensation cure<\/td>\n<td>Odour, extractables<\/td>\n<\/tr>\n<tr>\n<td>Peroxide fragments<\/td>\n<td>Peroxide cure<\/td>\n<td>Highest CVCM<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n<p class=\"tablecap\">Table 1 \u2014 What silicone releases and what each volatile does.<\/p>\n<table>\n<thead>\n<tr>\n<th>Applicazione<\/th>\n<th>CVCM target<\/th>\n<th>Typical route<\/th>\n<\/tr>\n<\/thead>\n<tbody>\n<tr>\n<td>General sealing<\/td>\n<td>not specified<\/td>\n<td>Standard platinum<\/td>\n<\/tr>\n<tr>\n<td>Electronics enclosure<\/td>\n<td>0.15%<\/td>\n<td>Post-cured platinum<\/td>\n<\/tr>\n<tr>\n<td>Optics and sensors<\/td>\n<td>0.10%<\/td>\n<td>Post-cured, low volatiles<\/td>\n<\/tr>\n<tr>\n<td>Space \/ vacuum<\/td>\n<td>0.05%<\/td>\n<td>Low outgassing grade<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n<p class=\"tablecap\">Table 2 \u2014 CVCM targets by application.<\/p>\n<div class=\"faq\">\n<h3>What does silicone outgassing release?<\/h3>\n<p>Mostly low molecular weight cyclic siloxanes such as D4, D5 and D6, plus water and, for condensation cure systems, the cure byproduct.<\/p>\n<h3>Does platinum cured silicone outgas?<\/h3>\n<p>Yes, though less than peroxide cure. Platinum cure leaves no reaction byproduct but still contains free cyclic siloxanes that evaporate over time.<\/p>\n<h3>What is CVCM?<\/h3>\n<p>Collected volatile condensable materials, from ASTM E595. It measures what deposits on a cold surface, which is the number that matters for optics and sensors.<\/p>\n<h3>How do I reduce silicone outgassing?<\/h3>\n<p>Post-cure above the service temperature. Four hours at 200 C cuts mass loss from 1.8 to 0.45 percent; longer times give diminishing returns.<\/p>\n<h3>Why does my enclosure window fog up?<\/h3>\n<p>Volatiles from the silicone gasket have nowhere to escape in a sealed box, so they condense on the coolest surface, usually the window.<\/p>\n<h3>What CVCM should I specify?<\/h3>\n<p>0.10 percent for optics and sensors, 0.05 for vacuum and space. Specify the test method as well, because 'low outgassing' on its own means nothing.<\/p>\n<\/div>\n<div class=\"cta\">\n<p class=\"cta-h\">Fogging or drifting in a sealed unit?<\/p>\n<p>Send the assembly and the service temperature. We will tell you whether it needs a post-cure, a different cure chemistry or a low outgassing grade.<\/p>\n<p><a class=\"btn\" href=\"https:\/\/uplastech.com\/it\/silicone-rubber\/\">Talk to our silicone team<\/a>\n<\/div>\n<div class=\"rel\">\n<h4>Continue reading<\/h4>\n<ul>\n<li><a href=\"https:\/\/uplastech.com\/it\/silicone-post-curing\/\">Silicone Post Curing<\/a><\/li>\n<li><a href=\"https:\/\/uplastech.com\/it\/silicone-degassing-vacuum\/\">Silicone Degassing Under Vacuum<\/a><\/li>\n<li><a href=\"https:\/\/uplastech.com\/it\/silicone-compression-set\/\">Silicone Compression Set<\/a><\/li>\n<li><a href=\"https:\/\/uplastech.com\/it\/silicone-bubbles-voids\/\">Silicone Bubbles and Voids<\/a><\/li>\n<li><a href=\"https:\/\/uplastech.com\/it\/silicone-gasket-seal\/\">Silicone Gasket Seal<\/a><\/li>\n<\/ul>\n<\/div>\n<\/div>","protected":false},"excerpt":{"rendered":"<p>Silicone is chosen for sealed enclosures because it is stable. Then the window fogs, the sensor drifts and the optics haze, and the cause is the gasket nobody suspected.<\/p>","protected":false},"author":1,"featured_media":7270,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[39],"tags":[],"class_list":["post-9055","post","type-post","status-publish","format-standard","has-post-thumbnail","hentry","category-silicone-rubber-products"],"meta_box":{"post-to-quiz_to":[]},"_links":{"self":[{"href":"https:\/\/uplastech.com\/it\/wp-json\/wp\/v2\/posts\/9055","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/uplastech.com\/it\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/uplastech.com\/it\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/uplastech.com\/it\/wp-json\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/uplastech.com\/it\/wp-json\/wp\/v2\/comments?post=9055"}],"version-history":[{"count":1,"href":"https:\/\/uplastech.com\/it\/wp-json\/wp\/v2\/posts\/9055\/revisions"}],"predecessor-version":[{"id":9067,"href":"https:\/\/uplastech.com\/it\/wp-json\/wp\/v2\/posts\/9055\/revisions\/9067"}],"wp:featuredmedia":[{"embeddable":true,"href":"https:\/\/uplastech.com\/it\/wp-json\/wp\/v2\/media\/7270"}],"wp:attachment":[{"href":"https:\/\/uplastech.com\/it\/wp-json\/wp\/v2\/media?parent=9055"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/uplastech.com\/it\/wp-json\/wp\/v2\/categories?post=9055"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/uplastech.com\/it\/wp-json\/wp\/v2\/tags?post=9055"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}