一车回收PET瓶片拉回厂里，洗干净造粒，测了个特性黏度，只有0.55dL/g，比新料的0.75差一大截。注塑出来的杯子一摔就裂，只能当低价回料卖给做打包带的。老板盯着这堆瓶片发愁：料便宜是便宜，可做不了正经产品，这价怎么上得去？
回收料头疼的事，十有八九出在分子量上。塑料每挤一次、热一次，分子链就断一截，链一短，粘度下来、强度垮掉，只能越卖越低档。扩链剂这东西，干的就是把断了的链重新接长，让再生料性能回春。这一篇把它讲明白。
先上一张扩链剂速查总表，把主流体系、关键参数、典型基材和添加范围列清楚。
| 体系 | 代表品种 | 关键参数/特性 | 典型基材 | 添加比例 |
|---|
| 环氧类 | 多官能环氧低聚物 | 反应温和、耐水解、扩链稳定 | rPET/rPBT/PC | 0.3%-1.5% |
| 噁唑啉类 | BOZ双噁唑啉 | 封羧基快、提黏度 | rPA/rPET | 0.3%-1.0% |
| 异氰酸酯类 | MDI型 | 增黏快、活性高 | rPU/部分聚酯 | 0.2%-0.5% |
| 环氧母粒 | 载体母粒 | 分散好、易计量 | rPET/rPA | 0.5%-2.0% |
| 复合型 | 环氧+噁唑啉复配 | 多端基反应 | 高老化回收料 | 0.5%-1.5% |
注：以上为行业通用范围，具体牌号、特性黏度提升幅度以厂家TDS及反应挤出实测为准；扩链效果与回料老化程度强相关。
回料不是不能用，是它的分子链已经被热加工短过一次
先把一个常识掰过来：回收料卖不上价，不是因为脏，也不是因为颜色差，是因为分子量掉了。新料从工厂出来，分子链又长又整齐，熔体粘度够、强度够。可塑料经过收集、清洗、多次挤出造粒，每一次高温螺杆剪切，链就被剪断一截。断到一定程度，熔体稀得像水，注塑充模一塌糊涂，做出来的件一冲就裂。
行业里用特性黏度（IV）或者熔融指数（MFR）来盯这件事。rPET新片料IV能到0.75左右，回收老化几次后掉到0.55甚至更低；MFR则是反过来，越断越高。粘度低，料就撑不起正经制品，只能降级去做打包带、纤维这种对强度要求不高的活。
宁波市科隆新材料有限公司长期经营各类工程塑料及改性助剂，在再生PET、再生PA原料和扩链剂、抗水解剂、相容剂上有稳定货源。扩链剂这个品类，主力是环氧类和噁唑啉类——它分子上带多个反应性基团，专找断链端上的羧基、羟基，把一截截短链重新缝成长链，分子量和粘度就回来了。科隆新材按回料老化程度推荐扩链体系，试样按公斤级发，附反应挤出前后的黏度对比数据。
回料降级，降的不是颜色，是分子链的长度。
图1 扩链剂把断裂分子链重新接长的示意
扩链剂干的事，是把断成截的分子链重新接成长绳
机理说人话。你把分子链想成一根麻绳，用着用着断成了十厘米一截的短段，这堆短段揉在一起软塌塌没强度。扩链剂就像一种两头带钩的连接器，这头勾住一截短链的端基，那头勾住另一截，把十厘米的短段重新接成一米的长绳。长绳回来了，熔体有了粘度，注塑充模有力气，强度自然跟着回来。
常用的有两路。环氧类带多个环氧基团，反应温和、耐水解，挤出去不容易分解，rPET、PC、PBT都吃这套；噁唑啉类（比如BOZ）对羧基反应特别快，回收尼龙、回收PET里的端羧基多，用它封端提黏度很灵。还有异氰酸酯类，增黏快但活性高、对水分敏感，多用于PU体系。选型看基材端基，别拿错钩子。
有行业数据可参考：rPET里加0.5%-1.5%的环氧类扩链母粒，特性黏度能提升大约0.10dL/g，MFR明显降下来；再生PA用量略高，大约1%-3%。加太少，扩链反应跟不上降解，粘度上不去；加太多，可能交联过度、熔体变脆，还得靠小试定。
粘度上不来，注塑就是一滩软泥；分子量回来，性能才跟着回来。
回收料降级卖不上价，缺的就是把粘度拉回来那一步
这一节算账。厂家为什么要买扩链剂？损失场景很实在：一是回料粘度太低，注塑充模不全、飞边多、废品率高，一天下来废品堆一地；二是降级卖，本来能做注塑级的料，因为强度不够只能低价卖给低档制品，一吨料少卖一两千；三是掺新料补性能，掺得越多省料优势越薄，算下来没省多少。
扩链剂添加量看着小，0.3%-2%，却直接决定这堆回收料能卖到哪一档。按行业通用成本口径，助剂只占改性塑料吨成本的一小部分，可它让一批低价瓶片从打包带级跳回注塑级，这一跃就是一吨料的身价差。
省在哪：把低粘度回料拉回可用黏度，少掺新料，料本实打实降。稳在哪：反应挤出一次成型，批次黏度一致，注塑不飘。灵活在哪：回料老化重就多加点，料还新就少加点，用量跟着回料状态调。
下面按行业通用口径演个示例：1吨回收PET，瓶片料约6000元/吨量级，加1%环氧类扩链母粒（约3万元/吨量级），折每吨成本约300元。这三百块把IV从0.55拉回0.65以上，料从打包带级拉到注塑片材级，一吨多出的身价差远超这三百。
| 成本项 | 不加扩链剂 | 加1%环氧扩链母粒 | 差异说明 |
|---|
| 助剂成本 | 0 | 约+300元/吨 | 按母粒约3万元/吨、1%计 |
| 特性黏度IV | 约0.55dL/g | 提升约0.10dL/g以上 | 反应挤出后实测 |
| 能做的制品 | 打包带/纤维低档 | 片材/注塑级 | 身价提升一档 |
| 掺新料比例 | 要掺新料补性能 | 少掺或不掺 | 省新料钱 |
| 综合 | 料便宜但卖得贱 | 小投入抬升料档 | 算身价账才划算 |
注：为示例演算，瓶片与母粒单价为2026年市场通用参考行情，随上游波动；实际以当期报价与打样黏度核定。拿不准该选哪类扩链剂、加多少份的？把应用场景和月用量发来，帮你对牌号、算这笔综合成本账。
再说买现成改性再生粒料，还是拿回收料自己加扩链剂。买改性料省事，供应商把扩链、相容、配色都做了；但按行业通用成本口径，一吨改性粒料在裸料之上叠加挤出加工费约1000-1500元、包装费100-250元、管销财费约5%-10%，再加供应商利润，自改等于把这层加价省掉。
| 对比项 | 买改性再生粒料 | 回收料+扩链剂自改 |
|---|
| 料本 | 裸料价+加工包装+管销财+厂家利润 | 回收料加助剂裸价，通常更低(行业通用口径) |
| 灵活度 | 黏度固定，挑牌号 | 按回料状态调扩链剂用量 |
| 起订量 | 整吨起订 | 回收料随便进，助剂按袋补 |
| 货期 | 受供应商排产 | 自己造粒随用随调 |
| 合规数据 | 供应商给报告 | 自控配方，自留黏度检测数据 |
| 适合谁 | 用量小、没造粒线 | 有挤出线、回料来源稳、量大 |
边界得讲清楚：扩链是反应挤出，得有双螺杆设备和测黏度的条件；回料来源杂、污染重的时候，扩链也救不回来，得先分选清洗。如果厂里没有造粒和测试能力、或者量小摊不开试错，直接买调好的再生粒料更稳妥。认证密集的食品接触级，扩链后还得单独过迁移检测，别省这步。
回收料省下来的钱，别让黏度问题又全吐回去。
扩链不只救PET，尼龙、PLA、PC都在回春
一提扩链大家就想到回收PET，其实只要是缩聚型、易断链的料，回料都需要补分子量。哪些料吃扩链剂？下表逐一类说。
| 品类 | 典型场景 | 添加量范围 | 效果 | 注意事项 |
|---|
| rPET | 瓶片造粒、片材 | 0.5%-1.5% | 提IV、稳粘度 | 先干燥再反应挤出 |
| rPA6/66 | 回收尼龙造粒 | 1.0%-3.0% | 提分子量、增韧 | 含水必须先烘干 |
| PLA | 可降解制品回料 | 0.3%-1.0% | 补链、增黏 | 注意结晶与气味 |
| rPBT | 电子件回收料 | 0.5%-1.5% | 补黏度、稳强度 | 常配抗水解剂 |
| rPC | CD/光学件回收 | 0.3%-1.0% | 提黏度、控变色 | PC易水解控干燥 |
| rPP/rPE | 大量回收聚烯烃 | 0.2%-1.0% | 提熔体强度 | 反应型接枝更常用 |
| 再生PET纤维 | 纺丝级回收料 | 0.5%-1.5% | 满足纺丝黏度 | 纺丝对IV要求严 |
| 回收PC/ABS合金 | 家电外壳回收 | 0.3%-1.0% | 稳两相界面黏度 | 配合相容剂 |
这张表只给方向，扩链量要按回料实际老化程度打样。宁波市科隆新材料有限公司在再生PET、再生PA原料和环氧、噁唑啉扩链剂上常年有货，针对回收瓶片客户会按目标黏度推荐环氧母粒，针对回收尼龙客户会把扩链剂和抗水解剂一起配样，打样阶段提供公斤级试样和反应挤出前后的IV/MFR对比数据，先跑平行样再定批量。有回收料拿不准该加环氧还是噁唑啉、加多少的？把基材、回料老化程度、目标制品发来，先帮你看方向。
同样一车瓶片，扩链前后是两个身价。
废品站回来的瓶片，加了扩链剂又拉回注塑级
说个回料厂里天天在上演的桥段（情景示例，非特定客户）。华南一家做再生PET片材的厂，回收瓶片便宜，可造出来的粒料IV只有0.55，只能低价卖给做打包带的。客户想往食品包装片材靠，卡在黏度上。
宁波市科隆新材料有限公司给他们配了环氧类扩链母粒，在双螺杆挤出线上按1%比例反应挤出。造出来的粒料IV回到0.66，透明度和韧性都上去了，直接跨过了片材注塑的门槛。
变化在哪：一是料从打包带级升到片材级，一吨多卖一两千；二是不用再掺那么多新PET补性能，回收料利用率上来了；三是回料IV低了就多倒点母粒，IV还行就少倒，配方跟着原料状态走。前提还是有双螺杆和测IV的设备，没这个别硬上。
这个边界也要说透：扩链剂不是把垃圾变黄金。回料分选不干净、PVC和PE混进去了，加再多扩链剂也做不出均一的料。什么时候别自己上？回料来源杂、没有分选清洗线、或者制品要食品接触认证，先把分选和检测这关过了再说。
再生料值不值钱，先看分子量回不回得来。
黏度数据回来，再生料才算真正上岸
收尾给一张快速选型速查表，照着自己的回料对号入座。
| 你的回料 | 先测什么 | 推荐方向 | 什么时候别这么选 |
|---|
| 低IV回收PET | 特性黏度IV | 环氧母粒1%左右 | 污染重先分选 |
| 回收尼龙 | 含水率+黏度 | 噁唑啉+预烘干 | 不烘干别上 |
| 回收PC | 黏度+黄变 | 环氧扩链+干燥 | 水解严重先换料 |
| 回收PLA | 熔体强度 | 少量环氧 | 堆肥要求另查 |
| 杂混回收料 | 分选干净度 | 先分选再扩链 | 杂质多别硬扩 |
| 高老化回料 | 端羧基含量 | 环氧+噁唑啉复配 | 单剂不够再复配 |
回收料厂问得最多的几个问题
问：塑料扩链剂一般加多少合适？答：看基材和回料老化程度。rPET常用0.5%-1.5%，rPA用量略高约1%-3%，PLA、rPC这类0.3%-1%。加少了反应跟不上降解，加多了可能交联变脆，正确做法是从下限做起，测黏度往上加，别一次倒满。
问：扩链剂和交联剂有什么区别？答：方向正好相反。扩链剂是把断成截的短链接成长链，提高线性分子量和黏度，材料还是热塑的；交联剂是把长链之间搭成网状，让材料不再熔、变耐热耐溶剂。做再生料回春要的是扩链，不是交联，别拿交联剂当扩链剂用。
问：加了扩链剂粘度还是上不来，先查什么？答：先查回料干没烘干——含水率高，扩链剂先跟水反应，链没接上；再查加工温度和停留时间够不够，反应挤出得给足反应窗口；还不行就看回料是不是混了PVC、PE等杂料，杂质一多扩链均匀度就垮。
回收料不是废料，是没被接回长链的短绳子。
再生料要卖上好价，先把分子量接回来
宁波市科隆新材料有限公司长期经营再生PET、再生PA等回收原料及扩链剂，环氧类、噁唑啉类扩链母粒有稳定货源。不管你是做再生PET片材要提IV，还是做再生尼龙要补分子量，或者做PLA/PC回料要回春，都可以把制品、湿热工况和寿命要求告诉我们，按工况推荐扩链体系。
声明：本文涉及的品牌、商标及产品名称权归各自原厂所有。本文为第三方选材知识分享，文中提及的牌号、参数、价格、添加量、认证及应用案例仅供参考，具体以各生产企业官方最新资料及批次检测报告为准。本文不构成任何采购或投资建议，读者据此操作风险自担。
A truckload of recycled PET bottle flakes was brought back to the factory, washed, and pelletized. The intrinsic viscosity was measured at only 0.55 dL/g, much lower than the 0.75 of new material. The cups molded from it crack easily if dropped, and can only be sold as low-priced recycled material for making packaging straps. The boss is worried about this pile of flakes: the material is cheap, yes, but it can't be used for proper products. How could the price go up like this?
The headache with recycled materials is most likely due to the molecular weight. Every time plastic is extruded or heated, a segment of the molecular chain breaks. When the chains are shortened, the viscosity drops and the strength collapses, meaning the material can only be sold at lower grades. Chain extenders work by reconnecting the broken chains and restoring the performance of recycled materials. This article explains it clearly.
First, provide a quick reference summary table of chain extenders, clearly listing the mainstream systems, key parameters, typical substrates, and additive ranges.
| system | Representative variety | Key Parameters / Features | Typical substrate | Add ratio |
|---|
| Epoxy | Multi-functional epoxy oligomer | Mild reaction, hydrolysis-resistant, chain-extension stable | rPET/rPBT/PC | 0.3%-1.5% |
| Oxazoline class | BOZ bisoxazoline | Fast carboxyl group capping, viscosity enhancement | rPA/rPET | 0.3%-1.0% |
| Isocyanates | MDI type | Quickly thickening, highly active | rPU/partially polyester | 0.2%-0.5% |
| epoxy masterbatch | Carrier masterbatch | Well dispersed, easy to measure | rPET/rPA | 0.5%-2.0% |
| Composite | Epoxy Oxazoline Compound | Polyfunctional base reaction | High-aged recycled material | 0.5%-1.5% |
Note: The above is the general industry range. Specific grades, characteristics, and viscosity enhancement should be based on the manufacturer's TDS and actual measurement of reactive extrusion; the chain extension effect is strongly related to the degree of recycled material aging.
Recycled material is not unusable; it's just that its molecular chains have already been shortened once by thermal processing.
Let's get one common sense straight: recycled material doesn't sell for a high price, not because it's dirty, and not because of poor color, but because its molecular weight has decreased. When new material comes out of the factory, its molecular chains are long and orderly, with sufficient melt viscosity and strength. However, after plastics go through collection, cleaning, and multiple extrusions into pellets, each high-temperature screw shear breaks some of the chains. Once broken to a certain extent, the melt becomes as thin as water, injection molding fills poorly, and the finished parts crack immediately upon molding.
In the industry, intrinsic viscosity (IV) or melt flow rate (MFR) is used to monitor this matter. New rPET sheets can reach an IV of around 0.75, but after several rounds of recycling and aging, it drops to 0.55 or even lower; MFR is the opposite, increasing as the material breaks down. When the viscosity is low, the material cannot support proper products and can only be downgraded for use in items like packing straps and fibers, where high strength is not required.
Ningbo Kolon New Materials Co., Ltd. has long been engaged in the operation of various engineering plastics and modified additives, and has stable supply sources for recycled PET, recycled PA raw materials, chain extenders, hydrolysis inhibitors, and compatibilizers. As for the chain extender category, the main types are epoxy and oxazoline—they carry multiple reactive groups on their molecules, specifically targeting the carboxyl and hydroxyl groups at the ends of broken chains, sewing short chain segments back into long chains, restoring molecular weight and viscosity. Kolon New Materials recommends chain extender systems based on the aging degree of the recycled material, providing test samples at the kilogram scale, along with viscosity comparison data before and after reactive extrusion.
Recycled material degradation refers not to the color, but to the length of the molecular chains.
Figure 1 Schematic of chain extender recombining broken molecular chains
What a chain extender does is reconnect broken molecular chains into long ropes.
Explain the mechanism in simple terms. Think of a polymer chain as a rope. With use, it breaks into short segments of about ten centimeters each. These short segments, when piled together, are soft and lack strength. A chain extender works like a connector with hooks on both ends: one end hooks to the end of one short chain segment, the other end hooks to another segment, reconnecting the ten-centimeter pieces into a one-meter-long rope. Once the long rope is restored, the melt gains viscosity, injection molding becomes easier, and strength naturally returns.
There are two commonly used types. Epoxy compounds have multiple epoxy groups, react gently, are hydrolysis-resistant, and do not easily decompose when extruded; rPET, PC, and PBT all use this type. Oxazoline compounds (such as BOZ) react especially quickly with carboxyl groups; many of the terminal carboxyl groups in recycled nylon and recycled PET use this, making them very effective for end-capping and increasing viscosity. There are also isocyanate compounds, which increase viscosity quickly but are highly reactive and sensitive to moisture, mostly used in PU systems. The selection depends on the terminal groups of the base material; don’t use the wrong “hook.”
There is industry data available for reference: Adding 0.5%-1.5% of epoxy chain extender masterbatch to rPET can increase the intrinsic viscosity by about 0.10 dL/g, and the MFR drops significantly; for recycled PA, the usage is slightly higher, around 1%-3%. Adding too little, the chain extension reaction can't keep up with degradation and the viscosity won't increase; adding too much may cause excessive crosslinking and make the melt brittle, and small-scale tests are needed to determine the right amount.
If the viscosity doesn't rise, injection molding is just a lump of soft clay; once the molecular weight comes back, the performance follows.
Recycled material is downgraded and cannot be sold at a good price; what’s missing is the step of restoring the viscosity.
This section is about calculating the costs. Why do manufacturers buy chain extenders? The loss scenarios are very real: first, the recycled material has too low viscosity, causing incomplete molding in injection molding, more flash, and high scrap rates, leaving piles of waste by the end of the day; second, selling downgraded material—material that could have been used for injection-molding grade products has to be sold cheaply for lower-end products due to insufficient strength, losing a few thousand per ton; third, mixing it with new material to restore performance—the more you mix, the thinner the material-saving advantage becomes, so in the end, not much is actually saved.
The amount of chain extender added seems small, 0.3%-2%, but it directly determines which grade this batch of recycled material can be sold at. According to the common cost calculation in the industry, additives only account for a small part of the ton cost of modified plastics, yet they can upgrade a batch of low-priced bottle flakes from conveyor belt grade back to injection molding grade. This jump is the difference in the value of a ton of material.
Where it saves: Bringing low-viscosity recycled material back to usable viscosity, mixing in less new material, the material cost truly goes down. Where it stabilizes: Reactive extrusion for one-time molding, consistent batch viscosity, injection molding without fluctuation. Where it is flexible: If the recycled material is heavily aged, add more; if the material is still new, add less; the amount is adjusted according to the state of the recycled material.
Here is an example using standard industry terms: Recycling 1 ton of PET yields bottle flake material worth about 6,000 yuan/ton. Adding 1% of epoxy chain extender masterbatch (around 30,000 yuan/ton) amounts to a cost of about 300 yuan per ton. This 300 yuan can raise the IV from 0.55 to above 0.65, upgrading the material from strapping band grade to injection molding sheet grade. The added value per ton far exceeds this 300 yuan.
| Cost item | Without chain extender | Add 1% epoxy chain extender masterbatch | Difference Explanation |
|---|
| Additive cost | Zero | About 300 yuan/ton | Based on roughly 30,000 yuan/ton for the masterbatch, at 1% |
| Intrinsic Viscosity IV | Approximately 0.55 dL/g | Increase by about 0.10 dL/g or more | Measured after reactive extrusion |
| Products that can be made | Packing straps/fiber low-grade | Sheet / Injection Molding Grade | Increase in value by one level |
| Proportion of new material added | New material needs to be added to improve performance | Mix less or not at all | Save money on new materials |
| Comprehensive | Cheap materials but sold at a low price | Small investment lifts feed grade | It's only worth it when you calculate your own value. |
Note: For demonstration calculations, the unit prices of pellets and masterbatch are based on the general market reference prices in 2026 and fluctuate with upstream changes; the actual prices should be determined based on the current quotation and sample viscosity. Not sure which type of chain extender to choose or how much to add? Send your application scenarios and monthly usage, and we can help you select the grade and calculate this overall cost.
Moreover, when it comes to buying ready-made modified recycled pellets, you might as well take the recycled material and add the chain extender yourself. Buying modified pellets is more convenient, as the supplier handles chain extension, compatibilization, and color matching; however, according to the common industry cost standards, a ton of modified pellets adds about 1000-1500 yuan for extrusion processing, 100-250 yuan for packaging, and about 5%-10% for management, sales, and financial fees on top of the raw material, plus the supplier's profit. Doing it yourself means saving this added cost layer.
| Comparison item | Buy modified recycled pellets | Recycled Material Chain Extender Self-Modification |
|---|
| material cost | Raw material price, processing and packaging, sales and management expenses, manufacturer profit | The base price of recycled material plus additives is usually lower (industry common phrasing) |
| Flexibility | Fixed viscosity, choose the grade | Adjust chain extender dosage according to the status of returned material |
| Minimum order quantity | Minimum order: whole ton | Recycled materials can be added freely, additives should be replenished by the bag |
| Delivery time | Subject to supplier scheduling | Make granules yourself and adjust as needed |
| Compliance data | The supplier gives the report | Self-controlled formula, in-house viscosity test data |
| Suitable for whom | Small dosage, no granulation line | There is extruded line, stable source of reclaimed material, and large quantity |
Boundaries need to be clearly defined: Chain extenders are reactive extrusion processes and require twin-screw equipment and the ability to measure viscosity; if the recycled material comes from mixed or heavily contaminated sources, chain extension won't save it, and sorting and cleaning must be done first. If the plant lacks pelletizing and testing capabilities, or the quantity is too small to risk trial and error, it's more reliable to directly buy pre-compounded recycled pellets. For certification-intensive food contact grades, chain-extended materials still need to undergo separate migration testing, so don't skip this step.
The money saved from recycled materials shouldn't be entirely lost again due to viscosity problems.
Chain extension not only saves PET, but nylon, PLA, and PC are also rejuvenating
When it comes to chain extension, everyone thinks of recycling PET. In fact, as long as the material is condensation-type and easily breaks down, recycled material needs molecular weight supplementation. Which materials use chain extenders? The table below explains each type one by one.
| Category | Typical scenario | Addition range | Effect | Precautions |
|---|
| rPET | Bottle flake granulation, sheet | 0.5%-1.5% | Increase IV, stabilize viscosity | Dry first, then react and extrude |
| rPA6/66 | Recycling nylon granules | 1.0%-3.0% | Increase molecular weight, toughen | Moisture must be dried first |
| PLA | Recycled material from biodegradable products | 0.3%-1.0% | Chain repair, viscosity increase | Pay attention to crystallization and odor |
| rPBT | Electronic component recycling material | 0.5%-1.5% | Replenish viscosity, stabilize strength | Commonly used with hydrolysis inhibitors |
| rPC | CD/Optical Component Recycling | 0.3%-1.0% | Increase viscosity, control discoloration | PC easy hydrolysis controlled drying |
| rPP/rPE | Large-scale recycling of polyolefins | 0.2%-1.0% | Melting strength | Reactive grafting is more commonly used |
| Recycled PET fiber | Spinning-grade recycled material | 0.5%-1.5% | Meet spinning viscosity | Spinning has strict requirements for IV |
| Recycling PC/ABS alloy | Home appliance shell recycling | 0.3%-1.0% | Stabilize two-phase interface viscosity | Compatibility agent |
This table only provides guidance; the amount of chain extender should be determined according to the actual aging degree of the recycled material. Ningbo Kolong New Materials Co., Ltd. maintains a regular stock of regenerated PET, regenerated PA raw materials, and epoxy and oxazoline chain extenders. For customers using recycled bottle flakes, epoxy masterbatches are recommended based on the target viscosity; for customers recycling nylon, the chain extender and anti-hydrolysis agent are matched together. During the sampling phase, kilogram-level samples are provided along with IV/MFR comparison data before and after reactive extrusion. Parallel samples are run first before deciding on batch production. If you are unsure whether to add epoxy or oxazoline to the recycled material, or how much to add, send over the base material, degree of recycled material aging, and target product, and we will first help you assess the direction.
The same truck of bottles has two different values before and after the chain expansion.
The bottle flakes returned from the scrap station were turned back into injection molding grade after adding a chain extender.
Let me share a scenario that happens daily in recycling plants (example situation, not a specific customer). A plant in South China that produces recycled PET sheets acquires bottle flakes cheaply, but the pellets they produce have an IV of only 0.55, so they can only be sold at a low price to manufacturers making strapping tape. The customer wants to move towards food packaging sheets but is stuck on the viscosity.
Ningbo Cologne New Materials Co., Ltd. provided them with epoxy chain extender masterbatch, which was reacted and extruded on a twin-screw extruder at a 1% ratio. The resulting pellets had an IV of 0.66, and both transparency and toughness improved, directly surpassing the threshold for sheet injection molding.
Where the changes are: First, the material has been upgraded from the level for straps to the level for sheets, so you can sell an extra one to two thousand per ton; second, there’s no need to mix in so much new PET to boost performance, so the utilization of recycled material has increased; third, if the recycled material’s IV is low, add a bit more masterbatch, and if the IV is okay, add less, adjusting the formula according to the raw material’s condition. The prerequisite is still having a twin-screw extruder and IV measuring equipment; without these, don't force it.
This boundary also needs to be clarified: chain extenders are not going to turn waste into gold. If the recycled material isn't properly sorted, and PVC and PE get mixed in, no matter how much chain extender you add, you won't be able to produce a uniform material. When should you not try it yourself? If the source of the recycled material is varied, there is no sorting and cleaning line, or if the product requires food contact certification, you should first pass through the sorting and testing stage before considering it.
Whether recycled material is valuable depends first on whether the molecular weight can be recovered.
The recycled material can be considered truly successful only after the viscosity data comes back.
To wrap up, provide a quick reference chart for fast selection, and match it according to your own feedback.
| Your feedback | What should we test first? | Recommended direction | When will you stop choosing like this? |
|---|
| Low IV Recycled PET | Intrinsic Viscosity IV | About 1% epoxy masterbatch | Prioritize sorting heavily contaminated items |
| Recycle nylon | Moisture content Viscosity | Oxazoline Pre-drying | Do not use without drying |
| Recycle PC | Viscosity Yellowing | Epoxy chain extension drying | Change the material first if hydrolysis is severe |
| Recycling PLA | Melt strength | Small amount of epoxy | Composting requirements should be checked separately |
| Mixed recycled material | Sorting cleanliness | Sort first, then expand the chain | Too many impurities, don't force expansion |
| Highly aged recycled material | Terminal carboxyl content | Epoxy Oxazoline Compound | If a single dose is not enough, mix again |
The most frequently asked questions by recycling material plants
Q: How much plastic chain extender is generally appropriate? A: It depends on the substrate and the degree of recycled material aging. For rPET, 0.5%-1.5% is commonly used; for rPA, slightly higher at about 1%-3%; for PLA and rPC, around 0.3%-1%. If added too little, the reaction cannot keep up with degradation; if added too much, it may crosslink and become brittle. The correct approach is to start from the lower limit, measure viscosity, and increase gradually, rather than adding it all at once.
Q: What is the difference between a chain extender and a crosslinking agent? A: The directions are exactly opposite. A chain extender connects broken short chains into long chains, increasing the linear molecular weight and viscosity, and the material remains thermoplastic; a crosslinking agent forms a network between long chains, so the material no longer melts and becomes heat- and solvent-resistant. For rejuvenating recycled materials, what you need is a chain extender, not a crosslinking agent, so don’t use a crosslinking agent as a chain extender.
Q: Even after adding the chain extender, the viscosity still doesn't increase. What should I check first? A: First, check whether the recycled material has been dried—if the moisture content is high, the chain extender reacts with water first, and the chains won't link. Next, check if the processing temperature and residence time are sufficient; reactive extrusion needs to provide a full reaction window. If that still doesn't work, see if the recycled material is mixed with impurities like PVC or PE. When there are too many impurities, the chain extension uniformity collapses.
Recycled material is not waste; it is the short strands that have not been reconnected into long chains.
To sell recycled materials at a good price, first restore the molecular weight.
Ningbo Kolong New Material Co., Ltd. has long been engaged in the trade of recycled PET, recycled PA, and other recycled raw materials, as well as chain extenders. We have stable supplies of epoxy and oxazoline chain extender masterbatches. Whether you are trying to increase the IV of recycled PET sheets, supplement the molecular weight of recycled nylon, or rejuvenate PLA/PC regrind, you can provide us with your products, wet-heat conditions, and life requirements, and we will recommend a chain extender system based on the working conditions.
Statement: The brands, trademarks, and product names mentioned in this article belong to their respective original manufacturers. This article is a third-party material selection knowledge sharing. The grade, parameters, prices, dosage, certifications, and application cases mentioned herein are for reference only, and the specifics should be based on the latest official information and batch test reports from the respective manufacturers. This article does not constitute any purchasing or investment advice, and readers bear the risks if they act on this information.
