一批发往车企的PBT连接器外壳，装车前做湿热循环测试，85℃热水泡上一千小时，拿起来一掰就碎，冲击强度掉了四成。客户整批复测退回，配方师翻出工艺记录才发现：原料烘干没问题，问题出在配方里压根没加抗水解剂，酯键在热水里被一个个剪断。
PBT、PET、TPU这些带酯键的工程塑料，干着的时候结实得很，一沾热水就容易发脆。很多人以为是料不行，其实是没给分子链上那点防水保险。这一篇把抗水解剂讲透：它管什么、加多少、潮湿环境的工程件寿命差在哪。
先上一张抗水解剂速查总表，把主流品种、关键参数、典型制品和添加范围列清楚。
| 体系 | 代表品种 | 关键参数/特性 | 典型制品 | 添加比例 |
|---|
| 聚碳化二亚胺 | PCDI(聚合型) | 热稳低挥发、相容好、封端羧基 | PBT/PET/TPU工程件 | 0.5%-2.0% |
| 单体碳化二亚胺 | 位阻型芳香族CDI | 反应快、分子量小、易迁移 | PU/胶粘剂、短期场景 | 0.3%-1.0% |
| 位阻芳香族 | 改性PCDI | 耐温更高、加工不分解 | 玻纤增强PBT、汽车件 | 0.5%-1.5% |
| 复合型 | PCDI+抗氧复配 | 既封端又防热氧 | 热水管、户外工程件 | 0.8%-2.5% |
| 封端辅助 | 环氧扩链类 | 补链增黏、配合抗水解 | 再生PET/PBT | 0.3%-1.0% |
注：以上为行业通用范围，具体牌号与效果以厂家TDS及湿热老化实测数据为准；聚碳化二亚胺单价偏高，选型按工况取舍。
工程塑料怕的不是高温，是高温里混进去那点水汽
很多人有个误区：PBT、PET耐温一两百度，怕什么水？问题恰恰出在高温加水。这些材料分子链里藏着酯键（-COO-），平时很稳，可一旦遇上热水、湿热环境，水分子就去攻击酯键，把长链剪成一段段的。分子链一短，分子量往下掉，冲击强度跟着跳水，料就发脆、一碰就裂。
更麻烦的是水解会自己加速。酯键一断就冒出一个羧基（-COOH），这羧基反过来又催化更多酯键断，像滚雪球一样越断越快。这就是行业里说的自催化水解。你不先把它掐住，它自己会把整锅料越咬越碎。
宁波市科隆新材料有限公司长期经营各类工程塑料及助剂，在PBT、PET、PA原料和抗水解、扩链、偶联等功能性助剂上有稳定货源。抗水解剂这个品类，主力就是碳化二亚胺体系——它分子里带的-N=C=N-基团，专门去找水解产生的羧基，一口把它吃掉，变成稳定的酰脲结构，把自催化的链条掐断。科隆新材按客户的湿热工况推荐聚合型还是位阻型，试样按公斤级发，附湿热老化对比数据。
PBT不是用坏的，是被水汽一段段泡断的。
图1 碳化二亚胺封端酯键的作用示意
抗水解剂干的事，是把漏水的分子链缺口焊死
把机理说人话。你把聚酯分子链想成一根长水管，水解就是管壁上出现一个个小漏洞，水越漏越大。碳化二亚胺就像带焊枪的修补工，它哪个地方冒出羧基（漏水口），就过去把那个口焊死——羧基被它反应掉了，酸没了，自催化的雪球就滚不起来了。
这里要分清两种剂型。单体型碳化二亚胺分子量小，反应快，但容易往制品表面迁移、还有气味，适合短期或PU、胶粘剂这类场景。聚合型碳化二亚胺分子量大，耐高温、不怎么挥发、跟基材相容好，挤出去加工不分解，留在料里慢慢干活，工程塑料长期耐湿就靠它。选型别只看价格，工程件优先选聚合型。
有文献数据可参考：PBT在85℃热水浸泡1000小时后，没加抗水解剂的拉伸保留率掉到60%以下，加了聚碳化二亚胺的能保住85%以上。差距就这零点几个百分点的添加量，换来的是湿热测试过不过、整批货退不退。
水解是个自催化的恶性循环，掐断开头这一处，后面就慢下来了。
热水里泡三个月就发脆，差的就是这零点几个百分点
这一节算账。厂家为什么要买抗水解剂？损失场景很具体：一是做汽车连接器、传感器壳，客户要求85℃×1000h湿热循环后冲击保留率达标，没加抗水解剂的一批批复测不过；二是做户外灯具、水泵件、热水管件，装出去半年一年就开裂掉渣，售后索赔找上门；三是做再生PET/PBT，回料本身分子量已经偏低，一遇水脆得更快，卖不上价。
抗水解剂添加量看着小，典型0.5%-2%，但它守的是整批工程件在潮湿环境下的寿命。按行业通用成本口径，助剂总成本通常只占改性塑料吨成本的1%-5%，可缺了它，湿热测试这关就过不了，一次退货损失的是整批料加返工加客户信誉。
省在哪：加了抗水解剂，PBT/TPU件在湿热环境下寿命拉长，售后开裂索赔少。稳在哪：羧基被持续封端，批次之间湿热表现一致，客户复测不飘。灵活在哪：湿态要求高的客户多加点，干燥环境用的少加点，用量按工况调。
下面这笔账按行业通用口径演个示例：做1吨加20%玻纤的PBT耐水解料，PBT树脂约1.3万元/吨量级，聚碳化二亚胺按工业通用约8万元/吨量级、加1.5%，折每吨成本约1200元。这一千多块，换的是85℃热水1000小时后冲击保留率从不足60%拉到85%以上。
| 成本项 | 不加抗水解剂 | 加1.5%聚碳化二亚胺 | 差异说明 |
|---|
| 助剂成本 | 0 | 约+1200元/吨 | 按聚碳化二亚胺约8万元/吨、1.5%计 |
| 湿热后冲击保留 | <60%(文献口径) | >85%(文献口径) | 85℃×1000h热水浸泡 |
| 复测通过率 | 偏低，常整批复测 | 稳定达标 | 客户85℃循环测试 |
| 售后开裂 | 半年一年易裂 | 寿命明显延长 | 户外/热水件 |
| 综合 | 省了助剂钱，赔退货钱 | 小投入守住整批料 | 算售后账才划算 |
注：为示例演算，树脂与助剂单价为2026年市场通用参考行情，随上游波动；实际以当期报价与客户技术要求核定。拿不准PBT抗水解该用聚合型还是位阻型碳化二亚胺？把应用场景和湿热要求发来，帮你对牌号、算耐这笔寿命账。
再说买现成抗水解PBT改性料，还是拿PBT树脂自己加抗水解剂。买改性料省事，供应商把封端、偶联、抗氧都配好了；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%，工程料再加15%-25%利润，这层加价自己改就能省。
| 对比项 | 买抗水解改性粒料 | PBT树脂+抗水解剂自改 |
|---|
| 料本 | 含加工费+包装+管销财费+工程料利润 | 树脂加助剂裸价，通常更低(行业通用口径) |
| 灵活度 | 封端量固定，只能挑牌号 | 湿态要求高就多加点，按工况调 |
| 起订量 | 整吨起订 | 树脂吨起，助剂按袋灵活补 |
| 货期 | 受供应商排产 | 通用料现拿，调配方不换料 |
| 合规数据 | 供应商给整套报告 | 自控配方，需自留湿热检测数据 |
| 适合谁 | 用量小、不想碰配方 | 量大、工况多变、有混料测试能力 |
边界也得说清：自己改得有测湿热老化的条件，不然封端量合不合适全靠猜；如果客户要求整套第三方认证文件、或者用量很小摊不开试错成本，直接买认证改性料更省心。认证密集的汽车件，材料切换周期长，别图省那点加工费跳过验证。
这里要补一句容易被忽略的：抗水解剂不是万能的，它救不了已经受潮的料。PBT、PA这类料加工前该烘干还得烘干，含水率超标的料，再好的封端剂也顶不住螺杆里那点水汽。烘干管的是加工当下别水解，抗水解剂管的是制品用在潮湿环境里别水解，两码事，别拿一个替另一个。
潮湿环境里的工程件，寿命差就差在有没有给端羧基上保险。
抗水解不只PBT用，TPU、PET、尼龙都在抢它
一提抗水解大家就想到PBT，其实只要分子链里带酯键、酰胺键，遇湿都怕水解。下面这张表把常用基材怎么用抗水解剂、加多少列清楚。
| 品类 | 典型场景 | 添加量范围 | 效果 | 注意事项 |
|---|
| 玻纤增强PBT | 汽车连接器、传感器壳 | 0.5%-1.5% | 湿热后冲击保留高 | 加工温度别过高 |
| PET/rPET | 再生PET打包带、片材 | 0.5%-2.0% | 补端羧基、稳粘度 | 配合扩链剂效果更好 |
| TPU | 软管、薄膜、鞋材 | 0.5%-2.0% | 耐水解不发黏 | 聚酯型TPU尤其需要 |
| 聚酯型PU | 合成革、弹性体 | 0.5%-1.5% | 防潮解、防断裂 | 注意气味与迁移 |
| PA6/PA66 | 含水结构件、户外件 | 0.3%-1.0% | 封端、稳分子量 | 加工前必须烘干 |
| PC/合金 | PC/ABS湿热件 | 0.3%-1.0% | 缓解PC水解 | PC本身易水解先控干燥 |
| PLA | 可降解制品 | 0.5%-2.0% | 延长货架期、抗储存水解 | 与相容剂配合 |
| 热熔胶/胶粘剂 | 耐水胶黏 | 0.5%-1.5% | 封端、耐水粘接 | 选反应型剂型 |
这张表只给方向，具体封端量要按目标湿热条件打样。宁波市科隆新材料有限公司在PBT、PET、TPU原料和聚碳化二亚胺助剂上常年有货，针对汽车连接器客户会按85℃×1000h要求推荐聚合型PCDI搭配，针对再生PET客户会把抗水解剂和扩链剂一起配样，打样阶段提供公斤级试样和湿热老化对比数据，先跑平行样再定批量。有PBT、尼龙遇湿发脆拿不准加多少的？把基材、湿热工况、寿命要求发来，先帮你看该上聚合型还是复合型。
聚合型留料里干活，单体型跑表面凑热闹，工程件别用错。
户外连接器过不了热水循环，原来配方少了个封端的
讲个车间里常碰到的真事（情景示例，非特定客户）。华东一家做玻纤增强PBT汽车连接器的厂，一直买配好的抗水解改性粒料。客户新要求85℃×1000h湿热循环后冲击保留率不低于80%，改牌号又要重新送样认证，一来一回耽误交期。
宁波市科隆新材料有限公司给他们换了个思路：改用通用PBT树脂加玻纤、自己配抗水解剂。聚合型PCDI加1.5%，配方师在实验室跑了三批湿热平行样，冲击保留率稳在85%上下，客户复测一次通过。
变化在哪：一是不用再等供应商排产改牌号，封端量自己调；二是料本去掉了改性粒料那层加工费和利润加价；三是同样的PBT树脂，给高湿客户多加0.3%，干燥客户少加，配方灵活。前提还是那句——得有烘箱和湿热测试箱，没这个条件别硬上。
这个边界要讲透：自改不是省钱的万能钥匙。用量小、认证文件要整套、或者厂里没有湿热老化测试能力的时候，老老实实买认证过的改性料，比自己摸着石头过河稳。什么时候别自己改？客户要求第三方全项报告、或者封端量微调会影响整套认证的环节，就别硬省。
材料的寿命，一半写在配方里，一半写在有没有掐断自催化那一下。
湿态寿命不是玄学，封端数据说了算
最后给张选型速查表，按自己的制品找对应方向。
| 你的制品 | 先想这个 | 推荐方向 | 什么时候别这么选 |
|---|
| 汽车PBT连接器 | 85℃湿热循环 | 聚合型PCDI 1%左右 | 干燥室内件别多加浪费 |
| 聚酯型TPU软管 | 耐水解不发黏 | 聚合型PCDI | 聚醚型TPU本就耐水 |
| 再生PET片材 | 分子量偏低易脆 | PCDI配扩链剂 | 纯PCDI不提黏度 |
| 户外灯具PBT | 长期日晒加潮湿 | PCDI+抗氧复配 | 只加抗氧不封端不够 |
| PA含水结构件 | 加工易水解 | 少量PCDI+预烘干 | 不烘干光加助剂没用 |
| 热水管件 | 长期耐热水 | PCDI复配体系 | 普通通用料别硬上 |
没加抗水解剂的工程件，不是不能用，是不知道哪天遇水就脆给你看。
配方和采购最常问的三句话
问：抗水解剂一般加多少合适？答：看基材和湿热要求。PBT、TPU常用0.5%-2%，PA6/PA66这类0.3%-1%，高湿热工况往上加。先从0.8%左右做起，跑85℃热水老化看冲击保留率，再往上调，别一次加太多。
问：聚合型和单体型碳化二亚胺有什么区别？答：单体型分子量小、反应快，但易迁移、有气味，适合PU、胶粘剂这类短期场景；聚合型热稳定、低挥发、不迁移，工程塑料长期耐湿就选它。做汽车连接器这种长寿命件，别图便宜用单体型。
问：加了抗水解剂还是水解发脆，先查什么？答：先查料烘干没有——PBT、PA含水率超标，加工当下就水解，助剂挡不住；再查加工温度是不是过高，高温会把封端剂提前消耗；还不行就看基材本身老化程度，回收料降解太深，加抗水解剂不如先补分子量。
潮湿环境用的工程件，先把端羧基封上再谈耐用
宁波市科隆新材料有限公司长期经营PBT、PET、TPU、PA等工程塑料及抗水解剂，聚碳化二亚胺系列有稳定货源。不管你是做汽车连接器要过85℃湿热循环，还是做TPU软管要耐水解，或者做再生PET要补分子量，都可以把制品、湿热工况和寿命要求告诉我们，按工况推荐聚合型还是复合型封端体系。
这一篇讲抗水解，同系列的扩链剂篇讲怎么把再生料的分子量接回来，两篇搭着用，潮湿环境的工程件才站得住。系列持续更新，下回聊怎么给回收料补分子量。
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 batch of PBT connector housings shipped to an automaker underwent damp-heat cycling tests before vehicle assembly. They were soaked in 85°C hot water for a thousand hours, and when picked up, they would snap easily. The impact strength had dropped by 40%. The customer returned the entire batch after retesting. The formulators checked the process records and found that the raw material drying was fine, but the problem was that the formula didn’t include any hydrolysis inhibitors, and the ester bonds were being cleaved one by one in hot water.
Engineering plastics with ester bonds like PBT, PET, and TPU are very strong when dry, but they tend to become brittle when exposed to hot water. Many people think the material is bad, but in fact, it's just that they haven't provided the molecular chains with a little waterproof protection. This article explains anti-hydrolysis agents in detail: what they do, how much to add, and why the lifespan of engineering parts differs in humid environments.
First, provide a quick reference table of anti-hydrolysis agents, listing the mainstream types, key parameters, typical products, and dosage ranges clearly.
| system | Representative varieties | Key Parameters / Features | Typical products | Add ratio |
|---|
| Polycarbodiimide | PCDI (Polymeric) | Thermally stable and low volatility, good compatibility, carboxyl-terminated | PBT/PET/TPU Engineering Parts | 0.5%-2.0% |
| Monomeric carbon diimide | Sterically hindered aromatic CDI | Fast reaction, low molecular weight, easy to migrate | PU/adhesive, short-term scenarios | 0.3%-1.0% |
| Sterically hindered aromatic | Modified PCDI | Higher temperature resistance, does not decompose during processing | Glass fiber reinforced PBT, automotive parts | 0.5%-1.5% |
| Composite | PCDI Antioxidant Compound | Seals the ends and prevents thermal oxidation | Hot water pipes, outdoor engineering components | 0.8%-2.5% |
| End Sealing Assistance | Epoxy chain extender type | Chain extension and viscosity enhancement, combined with hydrolysis resistance | Recycled PET/PBT | 0.3%-1.0% |
Note: The above is the general industry range. Specific grades and performance should be based on the manufacturer's TDS and actual data from damp heat aging tests; the unit price of polycarbodiimide is relatively high, and selection should be made according to operating conditions.
What engineering plastics fear is not high temperatures, but the moisture mixed in by the heat
Many people have a misconception: PBT and PET can withstand temperatures of 100–200 degrees, so why worry about water? The problem actually lies in adding water at high temperatures. These materials have ester bonds (-COO-) hidden in their molecular chains, which are normally very stable, but once they encounter hot water or a humid, hot environment, water molecules attack the ester bonds, cutting the long chains into segments. When the molecular chains shorten, the molecular weight drops, the impact strength plummets, and the material becomes brittle and cracks at the slightest touch.
What's even more troublesome is that hydrolysis accelerates on its own. Once an ester bond breaks, a carboxyl group (-COOH) appears, and this carboxyl group in turn catalyzes the breaking of more ester bonds, snowballing faster and faster. This is what the industry calls autocatalytic hydrolysis. If you don't stop it in time, it will keep breaking down the entire batch on its own.
Ningbo Kolon New Materials Co., Ltd. has long been engaged in the business of various engineering plastics and additives, with stable supply sources for PBT, PET, PA raw materials, and functional additives such as hydrolysis stabilizers, chain extenders, and coupling agents. In the category of hydrolysis stabilizers, the main type is the carbodiimide system — the -N=C=N- group in its molecule specifically targets carboxyl groups generated by hydrolysis, consuming them and transforming them into a stable urea structure, effectively breaking the autocatalytic chain. Kolon New Materials recommends either polymeric or sterically hindered types according to the customer's humid heat conditions, sends samples on a kilogram scale, and provides comparative data on humid heat aging.
PBT wasn’t worn out; it was broken apart in segments by moisture.
Figure 1 Schematic diagram of the function of carbodiimide-terminated ester bonds
What the water-resistant agent does is weld shut the gaps in the leaking molecular chains.
Explain the mechanism in plain language. Think of a polyester molecule chain as a long water pipe. Hydrolysis is like small leaks appearing on the pipe wall, and the more water leaks, the bigger the holes get. Carbodiimide is like a repair worker with a welding torch; wherever a carboxyl group (leak) appears, it goes and welds that spot shut—the carboxyl group reacts with it, the acid is gone, and the self-catalyzing snowball effect can’t start.
Here, we need to distinguish between two types of formulations. Monomeric carbodiimide has a low molecular weight, reacts quickly, but tends to migrate to the surface of the product and has a noticeable odor, making it suitable for short-term applications or scenarios like PU and adhesives. Polymeric carbodiimide has a high molecular weight, is heat-resistant, not very volatile, and is compatible with substrates. It does not decompose during extrusion processing and gradually works while remaining in the material. Long-term moisture resistance of engineering plastics relies on it. When choosing, don't just look at the price; for engineering parts, polymeric types are preferred.
There is literature data available for reference: After soaking PBT in 85°C hot water for 1000 hours, the tensile retention rate drops below 60% without adding hydrolysis inhibitors, whereas adding polycarbonate diimide can maintain over 85%. The difference is just a few tenths of a percent of additive, which determines whether it passes the damp heat test and whether the entire batch is returned.
Hydrolysis is a self-catalyzing vicious cycle; if you cut off the very beginning, the rest will slow down.
Soaking in hot water for three months will make it brittle; the difference is just a fraction of a percent.
This section is about accounting. Why do manufacturers need to buy hydrolysis stabilizers? The loss scenarios are very specific: first, for making automotive connectors and sensor housings, customers require that the impact retention rate meets the standard after 85℃ × 1000 hours of damp-heat cycling, and batches without hydrolysis stabilizers consistently fail retesting; second, for making outdoor lamps, water pump parts, and hot water pipe fittings, after being installed for half a year to a year, they start cracking and flaking, leading to after-sales claims; third, for making recycled PET/PBT, the recycled material itself already has a low molecular weight, and it becomes brittle faster upon contact with water, making it hard to sell at a good price.
The amount of hydrolysis inhibitor added seems small, typically 0.5%-2%, but it safeguards the lifespan of the entire batch of engineered parts in humid environments. According to the industry's usual cost calculation, the total cost of additives usually accounts for only 1%-5% of the cost per ton of modified plastics. However, without it, the humid heat test cannot be passed, and a single return results in losses from the entire batch of material plus rework and customer reputation.
Where it saves: By adding an anti-hydrolysis agent, PBT/TPU parts have a longer lifespan in humid and hot environments, resulting in fewer after-sales claims for cracking. Where it is stable: Carboxyl groups are continuously end-capped, ensuring consistent performance in humid and hot conditions between batches, so customer retests show stable results. Where it is flexible: Customers with high moisture requirements add a bit more, while those in dry environments add less, adjusting the dosage according to working conditions.
Here's an example of this calculation using industry-standard methods: Producing 1 ton of hydrolysis-resistant PBT material with 20% glass fiber, the PBT resin costs around 13,000 yuan per ton, and polycarbonate diimide is about 80,000 yuan per ton in industrial practice, adding 1.5%, which translates to roughly 1,200 yuan added to the cost per ton. This extra thousand-odd yuan improves the impact retention rate after 1,000 hours in 85°C hot water from less than 60% to over 85%.
| Cost item | Without adding hydrolysis inhibitor | Add 1.5% polycarbodiimide | Difference Explanation |
|---|
| Additive cost | Zero | About 1,200 yuan/ton | Calculated at about 80,000 yuan/ton for polycarbodiimide, at 1.5% |
| Retain after damp heat shock | <60% (according to the literature) | >85% (according to the literature) | 85℃ × 1000h hot water soaking |
| Retest pass rate | Relatively low, often retested in batches | Stable and up to standard | Customer 85°C cycling test |
| After-sales cracking | Easily cracks in half a year to a year | Life expectancy has significantly increased | Outdoor / Hot Water Parts |
| Comprehensive | Saved money on additives, lost money on returns | Small investment to secure the entire batch of materials | It's only cost-effective when calculating after-sales accounts. |
Note: For illustrative calculation, the unit prices of resin and additives are based on the general market reference for 2026 and fluctuate with upstream changes; the actual prices should be determined according to current quotes and customer technical requirements. Unsure whether to use polymeric or hindered carbodiimide for PBT hydrolysis resistance? Send over the application scenario and humidity/heat requirements, and I can help you choose the grade and calculate the service life.
Furthermore, when it comes to buying ready-made hydrolysis-resistant modified PBT material, you could also just take PBT resin and add the hydrolysis stabilizer yourself. Buying modified material is more convenient, as the supplier has already matched the end-capping, coupling, and hydrolysis resistance; but according to industry standard cost calculations, a ton of modified pellets adds extrusion processing fees of about 1,000–1,500 yuan, packaging fees of 100–250 yuan, and management, sales, and financial expenses of about 5%–10% on top of the base material. Engineering-grade material then adds another 15%–25% profit, and you can save this markup by modifying it yourself.
| Comparison item | Buy hydrolysis-resistant modified pellets | PBT resin hydrolysis-resistant agent self-modified |
|---|
| material cost | Including processing fees, packaging, management and sales financial expenses, and engineering material profit | The base price of resin plus additives is usually lower (industry-wide standard). |
| Flexibility | The sealing quantity is fixed; you can only choose the grade. | If the wet condition requires it to be higher, add a bit more and adjust according to the working conditions. |
| Minimum order quantity | Minimum order: one ton | Resin billed by the ton, additives flexibly supplied by the bag |
| Delivery time | Subject to supplier scheduling | General materials are taken as is, and formulas are adjusted without changing materials. |
| Compliance data | The supplier provides the complete set of reports | Self-controlled formula, requires retention of humidity and heat test data |
| Suitable for whom | Small dosage, don't want to touch the formula | Large volume, variable operating conditions, capable of mixed-material testing |
Boundaries also need to be clarified: if you modify it yourself, you must have conditions to test for moisture, heat, and aging; otherwise, whether the end-use amount is appropriate is entirely a guess. If the customer requires a complete set of third-party certification documents, or the quantity used is very small making trial-and-error costs unaffordable, buying certified modified material directly is more worry-free. For automotive parts with dense certifications, material switching cycles are long, so don’t skip verification just to save a little processing fee.
Here’s a point that’s easy to overlook: hydrolysis inhibitors are not万能—they can't save materials that are already damp. PBT, PA, and similar materials still need to be dried before processing. For materials with excessive moisture content, even the best end-capping agents can't withstand the small amount of vapor inside the screw. Drying prevents hydrolysis during processing, while hydrolysis inhibitors prevent hydrolysis when the product is used in a humid environment. They're two different things; don’t use one as a replacement for the other.
The lifespan of engineering components in a humid environment depends on whether the terminal carboxyl group is protected.
Water resistance is not only used by PBT; TPU, PET, and nylon are all competing for it.
When it comes to hydrolysis resistance, everyone thinks of PBT. In fact, as long as the molecular chain contains ester bonds or amide bonds, it is susceptible to hydrolysis when exposed to moisture. The following table clearly lists how commonly used base materials use hydrolysis inhibitors and in what amounts.
| Category | Typical scenario | Addition range | Effect | Precautions |
|---|
| Glass Fiber Reinforced PBT | Automotive connectors, sensor housings | 0.5%-1.5% | High retention after damp-heat shock | Do not make the processing temperature too high |
| PET/rPET | Recycled PET strapping and sheets | 0.5%-2.0% | Supplement terminal carboxyl groups, stabilize viscosity | Works better when combined with a chain extender |
| TPU | Hoses, films, footwear materials | 0.5%-2.0% | Hydrolysis-resistant and non-sticky | Polyester-based TPU is particularly needed |
| Polyester-based PU | Synthetic leather, elastomer | 0.5%-1.5% | Moisture-proof and break-resistant | Pay attention to odor and migration |
| PA6/PA66 | Water-bearing structural components, outdoor components | 0.3%-1.0% | End capping, stabilize molecular weight | Must be dried before processing |
| PC/Alloy | PC/ABS humid heat parts | 0.3%-1.0% | Relieve PC hydrolysis | PC itself is prone to hydrolysis, so pre-dry first |
| PLA | Biodegradable products | 0.5%-2.0% | Extend shelf life, resist storage hydrolysis | Used in combination with a compatibilizer |
| Hot Melt Adhesive/Glue | Water-resistant adhesive | 0.5%-1.5% | Sealing, waterproof bonding | Choose a reactive dosage form |
This table only provides guidance; the specific end-sealing amount needs to be sampled according to the target humidity and heat conditions. Ningbo Coron New Materials Co., Ltd. has stock year-round of PBT, PET, TPU raw materials, and polycarbonate diimide (PCDI) additives. For automotive connector customers, they will recommend polymeric PCDI combinations according to the 85℃×1000h requirement. For recycled PET customers, they will combine the hydrolysis stabilizer and chain extender in the sample. During the sampling stage, kilogram-level samples and humidity-heat aging comparison data are provided, starting with parallel samples before determining mass production. Not sure how much to add when PBT or nylon become brittle when wet? Send over the substrate, humidity-heat conditions, and lifetime requirements, and we’ll first help you determine whether to use polymeric or composite type.
Work with aggregate-type leftovers, monomer-type is just for show on the surface, don't use the wrong parts for engineering pieces.
The outdoor connector can't handle hot water circulation; it turns out the formula was missing an end seal.
Let me tell a true story that often happens in the workshop (scenario example, not a specific customer). A factory in East China that makes fiberglass-reinforced PBT automotive connectors has always bought pre-mixed hydrolysis-resistant modified pellets. The customer newly requires that after 85°C × 1000h damp-heat cycling, the impact retention rate should not be less than 80%. Changing the grade means resubmitting samples for certification, and this back-and-forth delays delivery.
Ningbo Kelon New Materials Co., Ltd. gave them a new approach: switch to general-purpose PBT resin with glass fiber and prepare their own anti-hydrolysis agent. With 1.5% polymeric PCDI, the formulators ran three batches of wet-heat parallel samples in the laboratory, and the impact retention rate remained around 85%, passing the customer's retest in one go.
Where the changes are: First, no need to wait for the supplier to reschedule production or change grades; you can adjust the batch quantity yourself. Second, the material cost no longer includes the processing fee and profit markup for modified pellets. Third, for the same PBT resin, you can add 0.3% more for high-humidity customers and less for dry customers, making the formulation flexible. The prerequisite is still the same—it requires an oven and a humidity-heat test chamber; without these conditions, don’t force it.
This boundary must be clearly explained: self-modification is not a universal key to saving money. When the usage is small, a complete set of certification documents is required, or the factory lacks the capability for damp heat aging tests, it is more reliable to honestly purchase certified modified materials than to experiment on your own. When should you avoid self-modification? If the customer requires a full third-party report, or if small adjustments to the end product could affect the entire certification process, don’t try to cut corners.
The lifespan of a material is half determined by the formula and half by whether its self-catalysis has been interrupted.
Wet life is not mystical; the sealing terminal data decides.
Finally, provide Zhang with a quick selection reference table, and find the corresponding direction according to your own products.
| Your product | Think about this first | Recommended direction | When will you stop choosing like this? |
|---|
| Automotive PBT connector | 85°C humid heat cycling | About 1% of polymeric PCDI | Don't overuse dry room components, it’s wasteful |
| Polyester TPU hose | Hydrolysis-resistant and non-sticky | Polymer-type PCDI | Polyether-based TPU is inherently water-resistant |
| Recycled PET sheet | Low molecular weight is prone to brittleness | PCDI compatibilizer | Pure PCDI without mentioning viscosity |
| Outdoor lighting PBT | Long-term sun exposure combined with humidity | PCDI Antioxidant Compound | Adding only antioxidants without end-capping is not enough |
| PA Moisture-Containing Structural Component | Easily hydrolyzed during processing | Small amount of PCDI pre-drying | Without baking dry, just adding additives is useless. |
| Hot water pipe fittings | Long-term heat-resistant water | PCDI compound system | Don't force it with ordinary general-purpose material |
Engineering parts without anti-hydrolysis agents are not unusable, it's just that you never know which day they will become brittle when exposed to water.
The three most frequently asked questions about recipes and procurement
Q: How much hydrolysis inhibitor is generally appropriate? A: It depends on the substrate and the requirements for humidity and heat. For PBT and TPU, 0.5%-2% is common; for PA6/PA66, about 0.3%-1%; higher amounts are used for high humidity and high temperature conditions. Start with around 0.8%, run aging tests in 85°C hot water to check the impact retention rate, then adjust upwards, but don’t add too much at once.
Q: What is the difference between polymeric and monomeric carbodiimide? A: Monomeric has a small molecular weight and reacts quickly, but it tends to migrate and has an odor, making it suitable for short-term applications like PU and adhesives; polymeric is heat-stable, has low volatility, and does not migrate, making it the choice for engineering plastics with long-term moisture resistance. For long-life components like automotive connectors, don’t try to save money by using monomeric.
Q: Even after adding a hydrolysis inhibitor, it still becomes brittle due to hydrolysis. What should be checked first? A: First, check whether the material has been properly dried—if the moisture content of PBT or PA is above standard, hydrolysis occurs during processing and additives can't prevent it. Then check if the processing temperature is too high, as high temperatures can prematurely consume the end-capping agent. If that doesn’t solve it, consider the aging level of the base material itself; if recycled material is too degraded, adding hydrolysis inhibitors is less effective than first restoring the molecular weight.
For engineering components used in a humid environment, seal the terminal carboxyl groups first before talking about durability.
Ningbo Kelong New Materials Co., Ltd. has long been engaged in the operation of engineering plastics such as PBT, PET, TPU, PA, and hydrolysis inhibitors, and has a stable supply of polycarbodiimide series. Whether you are making automotive connectors that need to withstand 85°C humid heat cycles, TPU hoses that need hydrolysis resistance, or recycled PET that requires molecular weight replenishment, you can tell us about your products, humid heat conditions, and lifespan requirements, and we will recommend either a polymer-type or composite-type end-capping system based on the conditions.
This article talks about hydrolysis resistance, while the article on chain extenders in the same series explains how to restore the molecular weight of recycled materials. Used together, the two articles help engineering parts withstand humid environments. The series will continue to be updated; next time we'll discuss how to supplement the molecular weight of recycled materials.
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.
