237 改性尼龙按介质选型索引
开篇先讲个现场
前年接到一个热线电话，对方的语气带着火气：你们说 PA66 耐油，我们的齿轮在齿轮油里泡了两个月，怎么就烂了？把样件寄过来一看，问题不在耐油本身——那台设备的油温常年 110 度以上，而高温油里的添加剂会加速尼龙的水解类反应，常温耐油的数据到这里全部作废。
电话最后还是把问题解了：换成了高温体系。但这个电话让我下了个决心，把介质这条线单独写成一篇，因为介质选型踩坑的客户实在太多，而且踩的方式几乎一样：拿一个常温数据，去回答一个高温或长期浸泡的问题。
水和油是最常打交道的两类介质，也是被误解最深的两类。都说尼龙怕水，可热水壶把手用的就是改性尼龙；都说尼龙耐油，可上一段那个案例就是栽在油里。差在哪？差在温度、时间、浓度这三个变量上。
这篇索引把六类介质——水与热水、油与油脂、酸与碱、有机溶剂、盐雾与海水、食品与人体接触——逐一铺开，每类都讲清楚什么条件下安全、什么条件下要换体系、什么条件下必须实测。
最后还给了介质排查的方法，那是一张可以照着填的表：介质名称、浓度、温度、接触时长、是否有应力。填完这张表拿去找任何一家材料商，得到的答案都会比一句耐不耐油准确得多。
介质一：水与热水
冷水（常温）：PA66 可用，但要注意吸湿带来的尺寸变化。热水（60-80℃）：必须用耐水解 PA66（加碳二亚胺封端剂）。高温水（> 90℃）：PA66 撑不住，走 PA12、PPS 或 PPSU。
关键提醒：PBT 和 PET 不耐热水水解——很多人误以为它们不吸水就耐水，恰恰相反。洗碗机、热水器、冷却系统要特别注意。
介质二：油与油脂
矿物油和液压油：PA66 耐油性良好，是最常用的选择。燃油（汽油、柴油）：PA66 优于 PE 和 PP，油箱和油管常用。但要加抗静电剂——静电火花点燃油气是真实风险。
润滑脂：PA 耐润滑脂，但高温下润滑脂会流失，要考虑自润滑改性。注意：油温升高会加速 PA 的老化，80℃ 以上的油要按高温工况校核。
介质三：酸与碱
这是 PA 的弱项——酰胺键在酸碱条件下水解加速。弱酸弱碱（pH 5-9）：耐水解 PA66 可以。强酸强碱：PA 不可用，走 PP、PVDF 或 PPS。
特别提醒：碱性环境对 PA 侵蚀最明显——洗涤剂 pH 10-12，洗碗机件要特别注意。PP 在酸碱环境下反而优于 PA，这是很多人不知道的。
介质四：有机溶剂
醇类（乙醇、乙二醇）：PA 在醇类中会溶胀，长期接触要评估——液冷系统的乙二醇溶液必须用耐水解牌号。酮类和酯类：PA 耐受性一般，要具体验证。芳香烃和卤代烃：PA 耐受性较好。
通用原则：塑料在有机溶剂中都会有一定溶胀，关键是溶胀后性能是否还在可接受范围。
介质五：盐雾与海水
盐雾本身对 PA 基体侵蚀不大，但会侵蚀玻纤——玻纤中的碱金属离子会析出，导致增强效果下降。海边和海上应用：要用耐水解玻纤（无碱或低碱玻纤）或者直接选 PPS。
另外要加耐候体系——海上紫外剂量大。户外 + 盐雾 + 紫外是三重考验。
一张排查表救回的订单
去年一个做咖啡机的客户，蒸汽阀的密封座老在半年内失效，前供应商换了三种料都没解决，客户已经在考虑改成金属件，成本要涨六成。我们介入后没有急着推料，先让客户填介质排查表：介质是水和水蒸气，温度标称 100 度，接触时长每天累计四小时，有装配应力。
表填到一半，问题就露出来了——标称 100 度是锅炉出口的温度，密封座实际位置的温度实测 128 度，客户自己都没测过这个点。温度修正之后，选型从普通增强 PA66 跳到高温档，同时把装配预紧的结构做了小改，应力集中降下来。改进后的验证件已经跑了一年半没有失效率上升。
这个案子我经常讲给新同事听，因为它的结论很朴素：介质问题十有八九不是介质本身，是介质加上你没测过的温度、没算过的应力。排查表的价值就在于此，它逼着每个人把变量一个个填出来，变量齐了，答案自己会浮出来。
介质六：食品与人体
食品接触：必须有 GB 4806.7、FDA 21 CFR、EU 10/2011 认证。不是所有 PA 都有食品级牌号，必须查具体牌号的证书。人体接触（医疗）：要 ISO 10993 和 USP Class VI。
这两类不是"性能"问题，是"合规"问题——不合规不能上市，性能再好也没用。
介质选型的成本观
介质这张表用到深水区，会遇到一个绕不开的话题：为介质改体系的成本。从 PA66 跳到高温体系，单价可能翻倍；从普通料换成耐水解牌号，一公斤贵出几块。怎么权衡？我们的建议是算暴露面积和更换成本：接触介质的部件多大面积、失效之后换一次多少钱。
一个几克重的小卡扣，用贵料全包也就贵几块钱，没必要纠结；一个几公斤的壳体，就要认真算失效概率和失效后果。介质选型的终点不是最耐的料，是整个生命周期里最划算的方案。这条原则放在这里，给所有对着表犹豫的人。
介质排查的方法
三步：第一步：列全介质清单——包括使用介质、清洗介质、意外接触的介质；第二步：查相容性表——各材料厂家都有化学相容性表，按具体化学品查，不按大类查；
第三步：做浸泡验证——在实际温度和浓度下浸泡，测浸泡后的强度保持率和尺寸变化。第三步最可靠，相容性表只能作为初筛。
工程实测：4 条强制测试
测试1：热水。PBT/PET 不耐热水水解，PA 加抗水解剂可用——反直觉但重要。
测试2：碱性。洗涤剂 pH 10-12 对 PA 侵蚀明显——洗碗机件要注意。
测试3：盐雾。侵蚀玻纤而非基体——海边要用耐水解玻纤。
测试4：食品。必须查具体牌号的认证证书，不按材料种类判断。
边界声明
| 工况 | 推荐材料 |
|---|
| 常温水 | PA66（注意尺寸） |
| 60-80℃ 热水 | 耐水解 PA66 |
| > 90℃ 热水 | PA12 / PPS / PPSU |
| 油类 | PA66（加抗静电） |
| 强酸碱 | PP / PVDF / PPS |
| 食品医疗 | 查具体牌号认证 |
工程备忘
介质索引：热水用耐水解 PA，强酸碱用 PP/PPS，油用 PA，食品医疗查牌号证书。PBT 不耐热水是常见误区。
实战案例：常见踩坑与正解
踩坑一：按介质选材查到了结论但没查适用条件，直接套用出错。任何速查表都有前提，脱离前提的结论都是错的。正解：看到结论先找它成立的条件——温度、介质、时间、载荷类型，四项齐全才敢用。
踩坑二：照抄别人的选型，没考虑自己的工艺能力。同样的料，不同设备和模具打出来效果不同。正解：选型要结合自己的工艺水平，不要选超出设备能力的材料。踩坑三：把速查表当最终依据，不做实际验证。正解：速查表用来缩小范围，最终一定要打样验证。
延伸判断：最容易被漏掉的隐性变量
按介质选材的量产事故里，有一半不是料选错了，是隐性变量没控住。
第一个变量是含水率。PA 系材料出厂含水率、干燥条件、注塑前的存放时间，三者共同决定实际含水率，含水率不对，强度和外观都会变。
第二个变量是模具温度。模温低 20℃，表面浮纤和熔接痕强度可能差一倍。
第三个变量是装配后的时间。装完 24 h 和装完 30 天的扭矩、尺寸、密封压缩量都不一样。
这三个变量都不写在物性表上，但都写在失效报告里。
把这三件事写成一张表发给供应商，比打十通电话有用——按介质选材的选型沟通成本，基本都花在这几项反复确认上。
介质问答四则
问：耐介质数据哪里查最靠谱？ 供应商的化学耐受表加第三方浸泡数据，两相对照。单一来源的耐受表多是常温短时数据，长期高温场景务必自己加测。
问：浓度对耐受性影响大吗？ 影响可以非常大。同一种酸，稀溶液和浓溶液对尼龙的攻击性完全是两回事，查表时浓度和温度必须和你的工况对上，差着查就是白查。
问：混合介质怎么评估？ 拆成分逐项评估加实测确认。清洗剂、切削液这类复配介质，添加剂的攻击性往往超过主成分，纸面评估只能兜底，最终以实际浸泡验证为准。
问：食品接触件的选料顺序是什么？ 先定合规再定性能。有食品接触认证的牌号先筛出来，在合格清单里选性能匹配的。反过来先选性能再补认证，大概率要推倒重来。
排查表填写示范
介质排查表怎么填，拿一个实例示范。某客户送来一个阀门密封圈询价，我们给的表他这样填：介质名称——循环冷却水，添加缓蚀剂；浓度——按供应商配比，说不清具体成分；温度——标称常温，备注夏天机房可达四十五度；
接触时长——常年浸没；应力状态——法兰压紧，有压缩应力。就这一张表，三个改进点自动浮出来：缓蚀剂成分要拿到，夏天四十五度要按实际算，压缩应力要问清压缩量。后来实测机房水温五十二度，缓蚀剂里含胺类，这两个条件任何一个漏掉，选出的料都会出问题。表格不难，难的是每格都写真话，写实测值而不是标称值。
浸泡试验怎么做才作数
介质选型最终都要落到浸泡试验，试验怎么做才作数，给一套做法。样件用真实制品或同工艺试片，不能用注塑条件不一样的对比片，应力状态不同结论会偏。介质用工况里的真东西，冷却液就用产线那桶，别拿纯水替代。
温度按实测峰值设，再设一档加十度的加速组。时间按寿命折算，一年寿命至少泡八周，中途取点测重量尺寸力学三项变化。最关键的是带应力对照：一组自由浸泡，一组装在夹具上带装配应力泡，很多介质应力开裂只在后者上现形。
试验报告最后写清介质、温度、时长、应力四要素，没有这四要素的报告，将来翻出来没法用。
介质问题的一票否决项
介质排查多年，我们内部形成了几条一票否决项，直接分享。强碱高温环境，普通尼龙直接否，不用讨论浓度多低；长期水浸又受力的件，普通非耐水解体系否；介质成分说不清的工况，没实测之前不出方案。
这三条看起来保守，但每条背后都有真实的赔偿案例。介质选型允许冒险的是锦上添花的项目，不允许的是安全件和密封件。把否决项前置，谈判桌上能省掉大量无效方案，对方也更早知道你的专业边界在哪里。边界清晰的人，反而更容易赢得信任。
结语
关于我们，四句话——选料这件事，越早问越省事。
这类件的选料与试模，可以一起聊。
237 Modified Nylon Selection Index by Media
Let's start by sharing a live experience
Two years ago, I received a hotline call with a tone full of anger: You said PA66 is oil-resistant, but our gears have been soaked in gear oil for two months, how did they rot? When I sent the sample over to check, the problem wasn't the oil resistance itself—the oil temperature of that device was always above 110 degrees, and the additives in high-temperature oil would accelerate the hydrolysis reactions of nylon, so the room temperature oil resistance data was completely nullified here.
In the end, the phone solved the problem: switched to a high-temperature system. But this call made me decide to write a separate article about the medium line, because too many customers have made mistakes in choosing the medium, and the methods are almost the same: using room temperature data to answer questions about high temperature or long-term soaking.
Water and oil are the two types of media we deal with most often, but also the two most misunderstood. People say nylon is afraid of water, but the kettle handles use modified nylon; Everyone says nylon is oil-resistant, but the previous case was just about getting stuck in oil. What's the difference? It's in temperature, time, and concentration.
This index lays out six types of media—water and hot water, oil and fat, acid and base, organic solvents, salt spray and seawater, food and contact with the human body—one by one, clearly explaining under what conditions are safe, under which systems need to be changed, and under which conditions must be tested.
Finally, it also provides methods for checking the medium, which is a table you can fill out as follows: media name, concentration, temperature, contact duration, and whether there is stress. After filling out this form, you can contact any material supplier, and the answer will be much more accurate than just asking about oil resistance.
Medium 1: Water and hot water
Cold water (room temperature) :P A66 can be used, but be mindful of dimensional changes caused by moisture absorption. Hot water (60-80°C): must use hydrolysis-resistant PA66 (with carbodiimide terminator). High-temperature water (> 90°C) cannot hold :P A66, so use PA12, PPS, or PPSU.
Key reminder: PBT and PET are not resistant to hydrolysis of hot water—many people mistakenly think they are water-resistant because they do not absorb water, but the opposite is true. Special attention should be paid to dishwashers, water heaters, and cooling systems.
Medium 2: Oil and grease
Mineral oil and hydraulic oil: PA66 has good oil resistance and is the most commonly used choice. Fuel (gasoline, diesel) :P A66 is better than PE and PP, commonly used in tanks and pipes. However, antistatic agents must be added—static spark points and fuel gases pose real risks.
Grease: PA is resistant to grease, but it will lose at high temperatures, so self-lubricating modification should be considered. Note: Rising oil temperature accelerates PA aging; oil above 80°C should be checked under high-temperature conditions.
Medium 3: Acids and bases
This is PA's weak point—amide bonds accelerate hydrolysis under acidic and alkaline conditions. Weak acids and weak bases (pH 5-9): Hydrolysis-resistant PA66 is acceptable. Strong acids and bases: PA is not usable; PP, PVDF, or PPS are used.
Special reminder: Alkaline environments are most sensitive to PA corrosion—detergent pH 10-12, so dishwasher parts require special attention. PP actually outperforms PA in acidic and alkaline environments, which many people don't know.
Medium 4: Organic solvent
Alcohols (ethanol, ethylene glycol):P A swell in alcohols; long-term exposure requires evaluation—liquid cooling systems must use hydrolyzable grade of ethylene glycol solution. Ketones and esters: PA resistance is average and needs specific verification. Aromatic hydrocarbons and halogenated hydrocarbons: PA has good tolerance.
General principle: Plastics will swell to some extent in organic solvents; the key is whether their performance remains within acceptable ranges after swelling.
Medium 5: Salt spray and seawater
Salt spray itself does not significantly erode the PA matrix but does corrode glass fiber—alkali metal ions in the fiberglass precipitate, reducing reinforcement. Coastal and offshore applications: use hydrolysis-resistant glass fibers (alkali-free or low-alkaline fibers) or directly choose PPS.
Additionally, add weather-resistant systems—high UV dosage at sea. Outdoor + salt spray + UV is a triple test.
An order saved by a troubleshooting checklist
Last year, a customer who made coffee machines had steam valve sealing seats that failed within half a year. The previous supplier tried three types of materials but couldn't solve the problem. The customer is already considering switching to metal parts, which will increase costs by 60%. After we got involved, we didn't rush to push the material. First, we had the customer fill out the media inspection form: the media are water and steam, the nominal temperature is 100 degrees, the contact time is four hours per day, and assembly stress is present. Halfway through filling out the
form, the problem became clear—the nominal 100 degrees is the boiler outlet temperature, but the actual temperature at the sealing seat was measured at 128 degrees, which the customer never measured themselves. After the temperature correction, the selection jumped from ordinary reinforced PA66 to the high-temperature range, and the pre-tensioned assembly structure was slightly modified to reduce stress concentration. The improved validated parts have been running for a year and a half without any increase in failure rate.
I often tell new colleagues about this case because its conclusion is simple: the medium problem is almost never the medium itself, but the medium plus the temperature you haven't measured or calculated the stress. This is the value of the checklist—it forces everyone to fill in the variables one by one. Once the variables are complete, the answer will emerge on its own.
Medium 6: Food and Human Body
Food contact: Must have GB 4806.7, FDA 21 CFR, EU 10/2011 certification. Not all PAs have food-grade grades; you must check the specific grade certificate. Human contact (medical): ISO 10993 and USP Class VI.
These two categories are not about "performance," but about "compliance"—if it's non-compliant, it can't be marketed, and no matter how good the performance is, it's useless.
Cost Perspective on Media Selection
This media chart is used in deep waters, and you inevitably encounter a topic: the cost of modifying the system for the medium. Jumping from PA66 to high-temperature systems can double the unit price; Switching from ordinary material to hydrolysis-resistant grades costs a few more yuan per kilogram. How do you balance this? Our suggestion is to calculate the exposure area and replacement cost: the size of the part in contact with the medium, and the cost to replace it once after failure.
A small clip weighing a few grams is only a few yuan more expensive to wrap with expensive materials, so there's no need to worry about it; For a casing weighing just a few kilograms, the failure probability and consequences must be carefully calculated. The ultimate goal in media selection is not the most durable material, but the most cost-effective solution throughout the entire lifecycle. This principle is set here for everyone hesitating about the table.
Methods for media troubleshooting
Three steps: Step one: Make a full media list—including media used, cleaning media, and media that come into accidental contact; Step two: Check compatibility tables—each material manufacturer has a chemical compatibility sheet, check by specific chemical, not by general category;
Step three: perform soaking verification—soak at actual temperature and concentration, and measure strength retention and dimensional changes after soaking. Step three is the most reliable; the compatibility chart can only be used for preliminary screening.
Engineering Testing: 4 mandatory tests
Test 1: Hot water. PBT/PET is not resistant to hydrolysis by hot water; PA can be treated with anti-hydrolysis agents—counterintuitive but important.
Test 2: Alkaline. Detergent pH 10-12 causes significant corrosion to PA—pay attention to dishwashers.
Test 3: Salt spray. Corrodes glass fibers rather than substrates—use hydrolysis-resistant glass fibers at the beach.
Test 4: Food. You must check the certification for specific grades, not by material type.
boundary declaration
| operating conditions | recommended materials |
|---|
| room temperature water | PA66 (pay attention to dimensions) |
| 60-80°C; hot water | hydrolysis-resistant PA66 |
| > 90°C Hot Water | PA12 / PPS / PPSU |
| Oil | PA66 (Anti-static) |
| Strong Acid/Alkali | PP / PVDF / PPS |
| Food Medical | Check Specific Grade Certification |
Engineering Memo
Medium Index: Hot water uses hydrolysis-resistant PA, strong acids and alkalis use PP/PPS, oil uses PA, food medical check brand certificate. PBT is not resistant to hot water, which is a common misconception.
Practical Case: Common pitfalls and correct answers
Pitfall 1: Found conclusions based on medium selection but didn't check applicable conditions, and directly applied them incorrectly. Every quick reference sheet has premises; conclusions that deviate from the premise are wrong. Correct answer: When you see a conclusion, first look for the conditions that hold it—temperature, medium, time, load type. Only use it when all four are complete.
Pitfall 2: Blindly copying others' mold selections without considering your own process capability. The same material produces different results with different equipment and molds. Correct answer: Choose based on your own process level, avoid materials beyond the equipment's capacity. Pitfall 3: Use the quick reference table as the final basis, without actual verification. Correct answer: The quick reference table is used to narrow the scope; ultimately, sample verification is necessary.
Extended judgment: The most easily missed hidden variable
In mass production accidents based on material selection, half of them are not due to wrong material selection but because the hidden variable was not controlled.
The first variable is moisture content. For PA-based materials, the actual moisture content is determined by factory moisture content, drying conditions, and storage time before injection molding. If the moisture content is incorrect, strength and appearance will change.
The second variable is mold temperature. If the mold temperature is 20°C lower, the surface float fiber and weld strength may differ by half.
The third variable is the time after assembly. Torque, size, and seal compression amount after 24 hours and 30 days after installation are all different.
None of these three variables are listed in the physical property table, but they are all written in the failure report.
Writing these three things into a single sheet and sending it to suppliers is more useful than making ten phone calls—since the communication costs for media selection and material selection are basically spent on repeated confirmation of these items.
Four Media Q&A questions
Q: Where is the most reliable place to check media resistance data? Suppliers' chemical resistance tables combined with third-party immersion data are cross-referenced. Single-source tolerance tables mostly contain short-term data at room temperature; be sure to add tests yourself in long-term high-temperature scenarios.
Question: Does concentration have a significant impact on tolerance? The impact can be very large. For the same acid, dilute and concentrated solutions are completely different in their aggressiveness to nylon. When checking the table, concentration and temperature must match your working conditions; checking any difference is pointless.
Question: How is the mixed medium evaluated? Component analysis and actual testing are used for confirmation. For mixed media like cleaning agents and cutting fluids, additives often have more aggressiveness than the main components. Paper evaluations can only provide a safety net, and actual soaking verification is the final standard.
Question: What is the material selection order for food contact parts? Compliance is determined first, then performance. Grades with food contact certification are first screened out, and those with matching performance are selected from the qualified list. Conversely, selecting performance first and then adding certifications will likely require starting over.
Sample of Filling Out the Troubleshooting Form
How to fill out the Medium Inspection Form? Here's an example. A customer sent a valve sealing ring for a quote. The form we gave was filled out like this: Medium name—circulating cooling water, added corrosion inhibitor; Concentration—based on supplier ratio, but specific composition is unclear; Temperature—nominal room temperature, note that in summer, the machine room can reach 45 degrees;
Contact duration—year-round immersion; Stress state—flange compression, compressive stress. With just this one table, three improvement points automatically emerged: the corrosion inhibitor ingredients must be obtained, 45 degrees in summer should be calculated based on actual conditions, and the compressive stress must be clearly inquired. Later, the actual test showed the machine room water temperature was 52 degrees, and the corrosion inhibitor contained amines. If either of these two conditions was missed, the selected material would have problems. The table wasn't difficult; the hard part was that each compartment was detailed and measured values accurately, not nominal .
How to perform immersion tests to count values
Medium selection ultimately falls into soaking tests; how to conduct tests to count is a set of methods. Samples use real products or test pieces made with the same process; do not use comparison sheets with different injection molding conditions; different stress states can lead to biased conclusions. Use real materials from operating conditions as media; coolant should be from the production line buckets, not pure water substituted.
Set temperature according to the actual peak value, then set an accelerator group with one level plus 10 degrees. The time is calculated by lifespan, with a minimum soaking life of eight weeks per year, and during the process, measurements were taken at points to measure the three changes in weight, dimensions, and mechanics. The most crucial point is stress control: one set of free immersion, one set mounted on fixtures with assembled stress bubbles. Many media stress cracks are only visible on the latter.
The test report ends with a clear description of the four elements: medium, temperature, duration, and stress. Without these four elements, the report will be useless in the future.
Media Issues' Veto-Item
Media Investigation After years of investigation, we have formed several veto items internally, which I will share directly. In high-temperature environments with strong alkalis, ordinary nylon is directly rejected, no need to discuss the concentration level; For parts subjected to long-term water immersion and stress, ordinary non-hydrolysis-resistant systems are excluded; For working conditions where the medium composition is unclear, no plans are prepared before actual testing.
These three points may seem conservative, but behind each one lies a real compensation case. Choosing the medium allows for risky projects that add the icing on the cake; what is not allowed are safety parts and seals. Putting the vetoed items upfront can save many ineffective solutions at the negotiation table, and the other party will know your professional boundaries earlier. People with clear boundaries are actually more likely to earn trust.
Conclusion
About us, four sentences—the earlier you ask about material selection, the easier it is to ask.
For these types of parts, material selection and mold trials can be discussed together
