{"id":7837,"date":"2025-10-27T09:00:00","date_gmt":"2025-10-27T09:00:00","guid":{"rendered":"https:\/\/uplastech.com\/recycled-resin-injection-molding\/"},"modified":"2025-10-27T09:00:00","modified_gmt":"2025-10-27T09:00:00","slug":"recycled-resin-injection-molding","status":"publish","type":"post","link":"https:\/\/uplastech.com\/pl\/recycled-resin-injection-molding\/","title":{"rendered":"Recycled Resin in Injection Molding: What the Percentage Actually Changes"},"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\/recycled-resin-injection-molding.jpg\" alt=\"Tensile strength and notched impact retained against regrind content, and melt flow rate against heat histories\" width=\"1536\" height=\"909\"><figcaption>Strength holds up as regrind content rises; impact falls away, and melt flow climbs with every pass through the machine.<\/figcaption><\/figure>\n<div class=\"toc\"><\/div>\n<h2 id=\"what-recycled-means\">Three different things called recycled<\/h2>\n<p>The word covers three materials with completely different risk profiles, and a specification that does not distinguish them is not a specification.<\/p>\n<table>\n<thead>\n<tr>\n<th>Typ<\/th>\n<th>\u0179r\u00f3d\u0142o<\/th>\n<th>Contamination risk<\/th>\n<th>Property loss<\/th>\n<\/tr>\n<\/thead>\n<tbody>\n<tr>\n<td>Regrind, in-house<\/td>\n<td>Sprues and rejects from the same press<\/td>\n<td>Very low, same material<\/td>\n<td>5 to 20 percent<\/td>\n<\/tr>\n<tr>\n<td>Post-industrial<\/td>\n<td>Another factory's scrap, often film or fibre<\/td>\n<td>Niski do umiarkowanego<\/td>\n<td>10 to 30 percent<\/td>\n<\/tr>\n<tr>\n<td>Post-consumer (PCR)<\/td>\n<td>Collection and sorting streams<\/td>\n<td>High, mixed polymer and odour<\/td>\n<td>20 to 50 percent<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n<p class=\"tablecap\">Table 1 - The three recyclate types. Most of the disagreement about recycled resin comes from two people meaning different rows of this table.<\/p>\n<p>In-house regrind is a process material. It has one heat history per pass, it is the same polymer, and it is dry if the virgin was dry. Post-consumer recyclate is a different proposition: it has been through a washing line, it carries traces of everything the packaging ever held, and its molecular weight distribution has already been widened by its first life.<\/p>\n<h2 id=\"property-loss\">What the percentage actually costs<\/h2>\n<p>The loss is not uniform across properties, and the pattern is consistent: stiffness and strength hold, toughness falls, and flow rises.<\/p>\n<table>\n<thead>\n<tr>\n<th>Regrind, %<\/th>\n<th>Tensile, %<\/th>\n<th>Notched impact, %<\/th>\n<th>MFR, %<\/th>\n<th>What it feels like<\/th>\n<\/tr>\n<\/thead>\n<tbody>\n<tr>\n<td>0<\/td>\n<td>100<\/td>\n<td>100<\/td>\n<td>100<\/td>\n<td>Reference<\/td>\n<\/tr>\n<tr>\n<td>20<\/td>\n<td>98<\/td>\n<td>95<\/td>\n<td>106<\/td>\n<td>No perceptible change<\/td>\n<\/tr>\n<tr>\n<td>40<\/td>\n<td>96<\/td>\n<td>88<\/td>\n<td>118<\/td>\n<td>Slightly easier to fill<\/td>\n<\/tr>\n<tr>\n<td>60<\/td>\n<td>93<\/td>\n<td>78<\/td>\n<td>135<\/td>\n<td>Flash starts to appear<\/td>\n<\/tr>\n<tr>\n<td>80<\/td>\n<td>89<\/td>\n<td>66<\/td>\n<td>160<\/td>\n<td>Short shots and flash together<\/td>\n<\/tr>\n<tr>\n<td>100<\/td>\n<td>84<\/td>\n<td>54<\/td>\n<td>190<\/td>\n<td>Brittle, and the tool flashes<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n<p class=\"tablecap\">Table 2 - Property retention against regrind content for a polypropylene copolymer, dry, at a fixed set of process settings.<\/p>\n<p>Tensile strength at 100 percent regrind is still 84 percent of virgin, which sounds acceptable. Notched impact is 54 percent, which is the number that decides whether the part survives a drop. A housing moulded from 100 percent regrind will pass a tensile test and crack when it is dropped, and the customer will describe that as a quality problem rather than a material one.<\/p>\n<p>The flow change is the second-order effect that causes most of the practical trouble. A melt flow rate that has risen 90 percent fills the cavity more easily, flashes at the parting line, and needs a different hold pressure. Running virgin and 100 percent regrind on the same settings guarantees that one of them is wrong.<\/p>\n<h2 id=\"why\">Why the properties fall<\/h2>\n<p>Four mechanisms, and they act at different rates.<\/p>\n<ul>\n<li>Chain scission: every thermal cycle shortens the polymer chain, and shorter chains mean lower viscosity and lower impact. This is the dominant effect in polypropylene and in most polyesters.<\/li>\n<li>Oxidation: each pass consumes antioxidant. Once the stabiliser is gone, the next pass degrades the polymer instead of the additive, and the loss accelerates.<\/li>\n<li>Contamination: a few percent of another polymer forms domains that act as crack initiators. One percent of PVC in polypropylene is enough to show.<\/li>\n<li>Moisture and hydrolysis: a polyester or a nylon that was not dried properly on the second pass is degraded in the barrel, and the effect compounds.<\/li>\n<\/ul>\n<p>Glass-filled regrind has a fifth mechanism: the fibre is already shorter, so a 30 percent glass compound made from regrind behaves like a 20 to 25 percent glass compound. The label on the box does not change; the part does.<\/p>\n<h2 id=\"design\">Designing a part that tolerates recyclate<\/h2>\n<p>If the recyclate content is a requirement rather than an experiment, the part should be designed for the worst batch, not the average one.<\/p>\n<ul>\n<li>Increase the wall by 10 to 15 percent rather than the rib count, because thicker sections tolerate a lower impact strength better than thin ones with sharp roots.<\/li>\n<li>Radius every internal corner to at least 0.5 mm. Recyclate fails at notches first, and a sharp corner is a notch.<\/li>\n<li>Avoid snap fits designed to the virgin strain limit. Use a living hinge only if the material is a purpose-made hinge grade, and never with PCR.<\/li>\n<li>Derate the design load by the impact retention, not the tensile retention. A 20 percent derate covers 60 percent regrind on most commodity resins.<\/li>\n<li>Specify the regrind content as a maximum with a verification method, not as a target.<\/li>\n<\/ul>\n<p>The verification method matters. A supplier can meet a 30 percent regrind claim by weight and still deliver a part with the flow of 60 percent, because the regrind was processed hotter. Melt flow rate on the moulded part is the cheapest check that the material is what the certificate says.<\/p>\n<h2 id=\"processing\">Processing changes that recyclate forces<\/h2>\n<p>A press running recyclate needs a different setup, and the differences are all about control rather than about capability.<\/p>\n<ul>\n<li>Dry it. Recyclate arrives with more moisture than virgin because it has more surface area and has been stored in bags that were opened.<\/li>\n<li>Lower the melt temperature by 5 to 10 degrees, because the viscosity is already lower and the antioxidant is already partly consumed.<\/li>\n<li>Reduce back pressure, and check the cushion: a lower viscosity melt leaks back past the screw more easily.<\/li>\n<li>Filter it if the application allows. A 40 to 60 micron screen removes the gels and the foreign particles that cause the visible defects.<\/li>\n<li>Vent the barrel if the recyclate carries volatiles, and expect more odour from PCR even when the numbers are in specification.<\/li>\n<li>Increase the purge between materials. A transition from PCR to virgin takes longer than virgin to virgin.<\/li>\n<\/ul>\n<div class=\"callout\">The most common recycled-resin failure is not a property loss, it is a drying failure. Recyclate has more surface area and more moisture, and a dryer set for virgin does not dry it.<\/div>\n<h2 id=\"compliance\">Compliance: where recycled resin is allowed<\/h2>\n<p>Food contact is the area where the answer is most often no, and where the reasoning is least understood. In the European Union, recycled plastic for food contact must come from a process authorised under Regulation 282\/2008, with a challenge test that demonstrates the process removes or deactivates the expected contaminants. Mechanical recycling of post-consumer packaging does not automatically qualify.<\/p>\n<p>In the United States, the FDA issues no-objection letters for specific recycling processes, based on surrogate challenge testing. A converter who buys PCR with a letter is in a different position from one who buys PCR without one, and the difference is the whole compliance argument.<\/p>\n<p>Outside food contact the constraints are lighter but not absent. Electrical and electronic parts need a flammability file that names the material, and a recyclate content change can require a re-listing. Automotive parts need the OEM's material specification, which usually allows regrind up to a stated percentage with a traceability requirement.<\/p>\n<h2 id=\"economics\">The economics, honestly<\/h2>\n<p>Recyclate is not automatically cheaper. In-house regrind is cheaper than virgin because the material has already been paid for, and the saving is real as long as the scrap rate is stable. Post-consumer recyclate is often priced at or above virgin commodity resin, because the sorting and washing cost more than the polymer is worth.<\/p>\n<p>The case for PCR is usually a customer requirement, a regulatory target or a brand commitment, not a cost saving. That changes what a moulder should optimise: not the resin price, but the scrap rate and the process stability, because a part that fails at 60 percent regrind costs far more than the difference between two resin prices.<\/p>\n<p>The honest summary is that regrind is a process material to be managed, and PCR is a different material to be qualified. Treating them as the same thing is how a project ends up with a part that passes every incoming inspection and fails in the field.<\/p>\n<div class=\"faq\">\n<h3>How much regrind can I use?<\/h3>\n<p>In-house regrind up to 25 to 30 percent is routine for most commodity resins, and up to 100 percent for non-structural parts if the tool and the process are adjusted. Impact-critical parts should stay below 20 percent.<\/p>\n<h3>Why does my part flash when I add regrind?<\/h3>\n<p>Because the melt flow rate has risen. Regrind fills more easily, so the same injection pressure over-packs the cavity. Lower the pressure and the hold, and check the cushion.<\/p>\n<h3>Does regrind affect colour?<\/h3>\n<p>Yes, especially with light colours and with PCR. Yellowing from oxidation and contamination from other colours both show, and a colour match approved on virgin will not hold at 50 percent regrind.<\/p>\n<h3>Can regrind be used in food contact parts?<\/h3>\n<p>In the EU only from an authorised recycling process with a challenge test. In the US only with an FDA no-objection letter covering the process. In-house regrind of food contact material is generally acceptable if it is the same material and is kept clean.<\/p>\n<h3>How many times can plastic be recycled?<\/h3>\n<p>Practically five to seven passes for polypropylene and polyethylene before impact and flow move outside a useful window, and fewer for polyesters and nylons because of hydrolysis. Each pass is a heat history and the antioxidant is finite.<\/p>\n<h3>How do I verify the regrind content?<\/h3>\n<p>Melt flow rate on the moulded part is the cheapest proxy. Thermogravimetric analysis for filled grades, and FTIR or DSC for polymer identification if contamination is suspected.<\/p>\n<\/div>\n<div class=\"cta\">\n<p class=\"cta-h\">Being asked to mould with recycled content?<\/p>\n<p>Tell us the percentage, the source and the impact requirement. We will tell you what the part has to change to carry it, and whether the tool can run the worst batch rather than the average one.<\/p>\n<p><a class=\"btn\" href=\"https:\/\/uplastech.com\/pl\/custom-injection-molding\/\">Talk to an injection engineer<\/a>\n<\/div>\n<div class=\"rel\">\n<h4>Continue reading<\/h4>\n<ul>\n<li><a href=\"https:\/\/uplastech.com\/pl\/regrind-recycled-content-extrusion\/\">Regrind and Recycled Content in Extrusion<\/a><\/li>\n<li><a href=\"https:\/\/uplastech.com\/pl\/recykling-gospodarka-o-obiegu-zamknietym-wplywa-na-wytlaczanie-tworzyw-sztucznych\/\">Recycling and the Circular Economy in Plastics<\/a><\/li>\n<li><a href=\"https:\/\/uplastech.com\/pl\/injection-molding-defects\/\">Injection Molding Defects<\/a><\/li>\n<li><a href=\"https:\/\/uplastech.com\/pl\/injection-molding-material-selection\/\">Injection Molding Material Selection<\/a><\/li>\n<li><a href=\"https:\/\/uplastech.com\/pl\/low-volume-injection-molding\/\">Low Volume Injection Molding<\/a><\/li>\n<\/ul>\n<\/div>\n<\/div>","protected":false},"excerpt":{"rendered":"<p>At 100 percent regrind, tensile strength is down 16 percent and notched impact is down 46. The property that moves least is the one on the data sheet the buyer is checking.<\/p>","protected":false},"author":1,"featured_media":7836,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[35],"tags":[],"class_list":["post-7837","post","type-post","status-publish","format-standard","has-post-thumbnail","hentry","category-injection-molding"],"meta_box":{"post-to-quiz_to":[]},"_links":{"self":[{"href":"https:\/\/uplastech.com\/pl\/wp-json\/wp\/v2\/posts\/7837","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/uplastech.com\/pl\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/uplastech.com\/pl\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/uplastech.com\/pl\/wp-json\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/uplastech.com\/pl\/wp-json\/wp\/v2\/comments?post=7837"}],"version-history":[{"count":0,"href":"https:\/\/uplastech.com\/pl\/wp-json\/wp\/v2\/posts\/7837\/revisions"}],"wp:featuredmedia":[{"embeddable":true,"href":"https:\/\/uplastech.com\/pl\/wp-json\/wp\/v2\/media\/7836"}],"wp:attachment":[{"href":"https:\/\/uplastech.com\/pl\/wp-json\/wp\/v2\/media?parent=7837"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/uplastech.com\/pl\/wp-json\/wp\/v2\/categories?post=7837"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/uplastech.com\/pl\/wp-json\/wp\/v2\/tags?post=7837"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}