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PA66 与 PPA 怎么选？它不是升级，是另一条平行线

塑料知识科普 发布时间: 2026-09-15 2805 阅读

72 PA66 and PPA: A Cross-Border Comparison of Aliphatic and Semi-Aromatic

1. Why PPA is not in the "General Selection Table"

PPA is the abbreviation for polyphthalamide, called '聚邻苯二甲酰胺' in Chinese, and it is a semi-aromatic polyamide. Its position is in the 'next level up' temperature resistance range compared to PA66, but it is one level better than PA46.

The reason it does not often appear on standard selection tables is not because it is 'niche,' but because:

Multiple suppliers have different names (Amodel, Arlen, Grivory HT, etc.), and there is not much information compiled in Chinese.

The price is significantly higher than PA66, slightly higher than or comparable to PA46.

The perception in the industry equating 'high temperature' with 'PPA' has not yet spread.

So what this article aims to do is to clarify the position of the PPA—it is not a substitute for the PA46, but another parallel line.

The boundary between PA66 and PPA is marked by a single process in many projects: reflow soldering. A customer making automotive sensor holders had an original PA66-GF30 design, but after SMT soldering, the holder deformed and the probe contact was poor.

A reflow soldering peak of 260 degrees, the long-term system of PA66 is simply not on this line. After switching to PPA, the deformation is pressed within the acceptable line, and the customer accepted the doubled price.

His statement is very straightforward: it's not that the PPA is good, it's that my process forces it. There are temperature requirements hidden in the process; understanding the process is more important than understanding the parameter sheet.

Later, whenever they initiated a project, they would first put up a process flow chart, and the materials team would pick materials according to the chart, cutting the number of arguments in half.

2. Differences in Chemical Structure

PA66: Hexamethylenediamine and adipic acid, aliphatic segments (flexible chains).

PPA: aliphatic diamine, aromatic dicarboxylic acid (isophthalic acid, terephthalic acid), semi-aromatic segments.

"Semi-aromatic" means that about 40-60% of the segments are aromatic rings. This variation brings three differences:

① Chain segment rigidification

The aromatic ring is on the main chain, making the chain segment more 'rigid.' The glass transition temperature increases, the melting point increases, and long-term heat resistance improves. The typical glass transition temperature of PPA is 120-150°C (PA66 is only 50-65°C), with a temperature resistance difference of 30-50°C.

② Significant decrease in water absorption rate

The aromatic ring itself is hydrophobic. The water absorption rate of PPA is usually between 0.5-1.5% (saturated state), which is 1/3 to 1/2 that of PA66.

③ Relative decline in liquidity

The rigid chain segments have weak mobility. The injection molding window is slightly narrower than that of PA66.

Combining the three points, the essential positioning of PPA is the combination of 'high temperature resistance and dimensional stability.' Having both of these at the same time is the direction that PA66 cannot replace.

3. Key Performance Comparison

IndicatorPA66PPADirection of difference
Glass transition temperature Tg (°C)50-65120-150PPA high about 70℃
Melting point (°C)255-265310-330PPA high about 60℃
Maximum continuous operating temperature (°C)120-150160-200PPA is about 40°C
Water absorption rate (23℃ saturated, %)2.0-2.50.5-1.5PPA is 1/3 to 1/2 of PA66
Tensile Strength (Unreinforced, MPa)80-9090-110PPA slightly high
Bending modulus (unreinforced, GPa)3.0-3.54.0-5.0PPA slightly high
Welding strengthmiddleVery tallPPA significant
Mold shrinkage rate1.2-1.70.5-1.2Lower PPA
Injection molding fluiditymiddleSlightly below averagePPA is weak
Glass Fiber Synergy EfficiencyTallVery highPPA-GF Extremely Stable
Unit price (standard grade, reference)1.0×2.8-4.0×PPA is significantly expensive
Processing difficultymiddleSlightly above averagePPA is somewhat difficult

Core differences: temperature resistance 50°C, water absorption -70%. These two differences are bidirectional: as temperature resistance increases by one level, water absorption decreases by one level. This is exactly why PPA is 'expensive for a reason'.

4. Where PPA Excels

① Long-term operation at 150-180℃

This temperature zone PA66 can no longer hold, and PA46 is also at its limit. Automotive turbochargers, transmission oil circuits, turbine surroundings, and PTC heater housings are all here. PPA can remain stable in this temperature zone up to 180°C (some grades 200°C).

② High temperature and high humidity dual working conditions

In traditional understanding, 'high heat resistance' and 'low water absorption' are mutually exclusive—PA46 has high heat resistance but high water absorption. But PPA breaks this rule: it has a heat resistance of 180°C while maintaining a water absorption rate of only 0.5-1.5%.

This means it can be used in high-temperature and high-humidity environments such as engine compartments, humid conditions, and outdoor equipment—PA66 will experience dimensional drift at 130℃ under high humidity, PA46 will also absorb water and become heavier in high humidity, whereas PPA remains stable in both respects.

③ Weld line strength of welded assemblies

The melting point of PPA is 310-330°C, much higher than PA66's 255-265°C. It has a wider welding temperature range. Comparing the welds of PA66-GF30 and PPA-GF30, PPA weld strength is 30-60% higher.

④ Creep and long-term dimensional stability

Under a load of 50 MPa at 150°C, the 1000-hour creep of PPA-GF30 is more than 50% lower than that of PA66-GF30. This is why many precision molds and long-life components choose PPA.

5. Where PA66 Excels

① Cost-performance ratio

The unit price of PA66 is 1/3 to 1/4 that of PPA. Unless there is also a requirement for 'high temperature resistance, dimensional stability, and long service life,' the premium on PPA is recovered slowly.

② Liquidity

The fluidity of PA66 is better than that of PPA. For complex geometries, thin walls, and long-process parts, PA66 is easier to fill, while PPA tends to have short shots in these parts.

③ Supply and Variety

PA66 has abundant global supply and a complete range of varieties. PPA has fewer suppliers (Süwi, BASF, DuPont, etc.), and the naming differs significantly among suppliers, making procurement and domestic substitution difficult.

④ Mold design and trial molding cycle

PPA has weak flowability and high mold temperature requirements, so the mold needs heated channels and a more complex temperature control system. This further increases the mold cost. PA66 can use ordinary molds, while PPA requires specialized molds.

6. The Locations of PPA and PA46

PPA is easily mistaken for a 'more expensive PA46'—so this section will first clarify this relationship.

MaterialMaximum temperature resistanceWater absorption ratePrice multiple (with PA66 = 1)Main Scene
PA66-GF30120-150℃2.0-2.5%1.0×Structural components, connectors, gears
PA46-GF30150-165℃12-15%2.5-3.5×High-temperature connectors and soldered wire components
PPA-GF30160-200℃0.5-1.5%2.8-4.0×High temperature and high humidity, wire bonding, precision components

As can be seen, PPA is not an upgrade of PA46; it is a parallel alternative to PA46—same price range, but with a huge difference in water absorption. If a project requires a temperature resistance of 160℃ while not having high water absorption, PPA is the right answer; PA46 is not.

7. Four Extended Judgments (General for Semi-Aromatic Compounds)

Judgment 1: Temperature resistance 160°C, water absorption 1.5%. These two indicators are the "entry ticket" for PPA. Very few other materials meet both of these criteria simultaneously. PPA holds a unique position in these two aspects, rather than being just a "slightly more expensive PA46".

Judgment Two: Mold cost is the invisible threshold of PPA. The molds required for PPA injection molding have more complex temperature control and hot runners than PA66. Mold investment is 30-80% higher than PA66. For small-batch projects, the unit price of PPA is high, making the project unprofitable.

Judgment Three: PPA on the wire-welded part is a "double advantage." Not only is the base material temperature-resistant, but the weld seam after wiring can still withstand the same temperature grade as the base material. PA46 base material can withstand high temperatures, but the weld seam temperature resistance may be one grade lower than the base material.

Judgment Four: High heat resistance does not equal high moisture resistance, and vice versa. PA46 has high heat resistance but absorbs a lot of water, while PPA has both. This combination is the true market position of PPA—don’t choose it based only on a single dimension of heat resistance.

8. Boundary Statement

Operating conditionSuggestion
Long-term ≤130℃, dry statePA66-GF30
Long-term 130-150°C, dry statePA66-GF35 or PA46-GF30
Long-term 130-150°C, wet statePPA-GF30
Long-term 150-180℃, dry statePPA-GF30
Long-term 150-180℃, wet statePPA-GF30 (Preferred)
Long-term ≥180℃Go PA6T / PA9T / PA10T / PA4T
Welded wire part Wet statePPA-GF30
Price sensitive Dry statePA66-GF30
thin-walled complex partsPA66

Appendix: Two selection examples

Example 1: Automotive Turbocharger Housing

Operating conditions: long-term 160°C, short-term 180°C; high cyclic load; wet conditions (condensed water).

Deduction:

160℃ long-term → PA66 eliminated

Wet state → PA46 high water absorption, not suitable

180℃ short time → PPA is better than PA46

High cycle → Long PPA fatigue life

Conclusion: PPA-GF30.

Example 2: PTC Heater Housing

Operating conditions: long-term 130℃, short-term 170℃; dry state; insulation required.

Deduction:

130℃ long-term → PA66 is okay, but 170℃ short-term is not

Dry state → Water absorption is not the key

Insulation → PA66 can also meet the flame retardant requirement

Overall → PPA at 170°C for a short time, long-term 130°C is a safer option

Conclusion: PPA-GF30. If it is only dry-state at 130°C for a long time and there is no requirement for 170°C short-term, PA66-GF30 is sufficient—it does not necessarily have to be PPA.

Industry insight: The easiest pitfall when selecting materials for temperature resistance is the mindset of 'you can't go wrong with a more expensive option.' We saw a project involving PTC heaters where they originally used PA66 flame retardant GF30, priced at 70 yuan/kg. The engineers thought that 'the customer requires higher temperature resistance' and switched to PPA, which costs 200 yuan/kg. In the end, the customer's actual operating conditions were 110°C for long periods and 130°C for short periods, so the temperature resistance advantage of PPA was never utilized, wasting the money. The core of material selection is to identify 'which aspect of the operating conditions is actually critical,' and then match that aspect to the material—advantages in other areas are mostly irrelevant.

The cost reduction cycle of an electronic water pump

The starting point is using PPA for the electronic water pump housing, but the customer thinks it's too expensive and wants to go back to PA66.

During the incubation period, a correct decision was made: conduct six months of thermal aging comparison first before making a decision. Under long-term conditions at 150℃, the bolt retention strength of PA66 flange surfaces decreases significantly.

The conclusion of the settlement is a compromise: parts in the high-temperature area retain PPA, while the low-temperature cover reverts to PA66; the cost per piece dropped by 20%, with not an inch lost in performance.

Cost reduction is not about changing materials, it's about splitting operating conditions. This case was later cited many times by their cost reduction meetings.

Evaluation of PA66 and PPA, three follow-up questions to start.

Follow-up Question 1: What is the peak temperature and frequency? Occasional peaks and long-term residence are two different answers.

Follow-up Question 2: Is it sensitive to water absorption? PPA has lower water absorption and is superior in precision fitting.

Follow-up Question 3: Is there a hydrolysis environment for PPA? PPA's hydrolysis rating in the coolant circuit is more stable; don't just look at the dry state.

Extension: Four-step rapid judgment (PA66 vs PPA direction)

Four-step comparison of "temperature and humidity resistance" is a viable action:

Step one: Mark the two lines of "long-term temperature + wet state" together. PA46 is heat-resistant but not moisture-resistant, while PPA is both temperature-resistant and moisture-resistant—this is the fundamental dividing line between the two groups.

Step 2: Measure the wire strength requirements. PPA wire welding is 30-60% higher than PA66. For projects requiring weld seam strength ≥80% base material, PPA is the more stable answer.

Step 3: Calculate costs. PPA costs 3-4 times more than PA66—only when "temperature resistance + moisture resistance + wire welding + long-term lifespan" are all met at once can this premium be recovered.

Step 4: Evaluate mold costs. PPA injection molding requires heating channels and temperature control systems, so molds cost 30-80% more than PA66. Using PPA for small batch projects is not cost-effective.

These four are useful because many projects "want to install PPA but don't know where PPA is." PPA is a requirement for all four essentials: "temperature resistance + moisture resistance + wire bonding + lifespan."

Practical: Three steps

Step one: Mark the two variables "temperature + wetness" together. PPA's temperature resistance of 180°C and 1.5% water absorption combination are not available in either PA66 or PA46.

Step two: wire welding tests must be done to ensure "same temperature as the base material." The weld temperature is often one notch lower than the base material—PPA's advantage over PA46 is more obvious for weld seams.

Step three: Calculate the "mold + raw material" dual accounts. PPA molds require 30-80% more input, and 3-4 times more raw materials. Short-term projects are not cost-effective—only consider projects with a lifespan of over 5 years.

Key Tips

If you have already chosen PPA: Note its processability window is narrower than PA66, mold temperature 150-180°C, material temperature 320-340°C. Molds need to heat the runner, otherwise the fiberglass will be exposed and the surface will darken.

Processing fee + mold fee is an invisible threshold; for small batch projects, "mold investment" must be included in the total account.

Closing with a three-question and three-answer post.

High-frequency issuesOne-sentence answer
Is PPA required for reflow soldering?For automotive SMT components, the peak value of 260°C is hardwire
PPA can PA46 be used?High-temperature overlapping sections are determined by water absorption and supply .
Is the price difference doubled?After splitting operating conditions, it often saves half of the value .
Does the mold need to be changed?Different shrinkage systems, new mold opening compensates with PPA

Another reverse case.

One project used PPA for room-temperature decorative parts because inventory was just right. As a result, the injection mold temperature couldn't keep up, and the parts became brittle and scrapped in two batches. PPA's process conditions are purely a burden on room-temperature parts; the material is neither good nor bad, but the wrong placement is all harm. Anti-aircraft guns hit mosquitoes; the high cost lies in the ammunition.

The origin of the numbers: two or three reasons

Why is reflow soldering 260°C hardwire? Solder melting and wetting require this temperature range, plus process allowance, so the peak value is only higher. In the furnace, the component must withstand not static temperature resistance at 260°C, but the rapid impact of heating and cooling. PA66's long-term system lags far from this line, so semi-aromatic PPAs can hold their ground.

This line is determined by the solder, not the plastic, so it is universal across the industry.

PPA Why is the water absorption so low? In the semi-aromatic structure, the benzene ring occupies a large space, the amide group density is diluted, and water molecules have fewer places to attach. Low water absorption means stable interlocking dimensions, benefiting precision parts and antenna components. Temperature and water absorption share the same advantage, which is the structural foundation for PPA to stand firm in automotive electronics.

Practical operation checklist: Six steps for reflow workpiece project initiation

Process roadmap should be posted first, material group should select materials for the process

Peak temperature and frequency separately recorded, occasional and normal occurrences should be priced separately

Coolant and hydrolysis risks separately, dry state data insufficient

New mold opened should compensate according to PPA shrinkage system, two-color comparison samples

Cost reduction should start from splitting operating conditions, high-temperature and normal temperature zones should be separated

and re-tested dimensions after passing through the furnace and written into first-piece inspection

Reflow welded part selection. Process steps are on page one, parameters on page two. If you read the order backwards, even if the quote is low, you still have to book rework.

Quick Judgment Manual: The three signals for PPA entry

SignalExplanation
SMT Reflow soldering process is within the routePeak 260°C is hard constraint
Long-term service of precision mating surfacesLow water absorption dimensional dividend
Coolant or damp environment presenceHydrolysis rating PPA is more stable

The first of the three signals is almost a one-pass item for automotive electronic components, while the last two determine the specific grade. Our experience is that posting the process roadmap on the first page of the selection meeting instantly doubles efficiency, because half the debate is actually about process steps, not materials.

There is a category of parts that are easily misjudged worth mentioning separately: seats close to motors and power devices. They are just reflow soldering, but they run at 150 degrees for a long time, with PA66 shaking at the boundary. For these parts, we recommend directly applying PPA, not for peak use but for years—constant edge conditions consume more material than occasional peak conditions.

The temperature recorder runs on the prototype for two weeks, and this judgment has a data foundation, more reliable than any analog.

One last note from an accounting perspective: PPA premiums should be recorded as "free after-sales." One client calculated the after-sales cost of the PPA cover separately; the three-year exemption repair fee just covered the material price difference, and from the fourth year onward, it became a net profit. No one usually calculates this kind of account; once a project is calculated, new projects are no longer hesitated to do so later.

PPA's mold ledger also has a noteworthy section: shrinkage compensation is measured based on the grade, not the manual general value. Within the PPA family, shrinkage differences between different glass fiber content and crystal modification are larger than those within the PA66 family. If molds are opened according to manual values, the first piece size usually requires repairs. After a loss once,

's mold factory wrote in the factory regulations "perform 20 mold shrink tests first when opening PPA molds," and since then, the number of mold repairs for PPA projects has been zero. Molds are heavy assets, and the initial testing costs are negligible compared to mold repair.

Conclusion

PPA This is not a replacement for PA46, but a parallel line.

PA66 is the main structural strength: temperature resistance of 130°C, water absorption of 2.5%, moderate price—the main choice for most industrial parts

PPA is suitable for high-temperature and moisture-resistant applications: temperature resistance 160-200℃, water absorption 0.5-1.5%, price 3-4×—used for precision parts and wired components that require both temperature and moisture resistance.

The starting point for selection is not 'which is more expensive or more stable,' but 'which aspect is my part limited by.' If limited in temperature resistance, moisture resistance, wiring, and lifespan, PPA is the correct choice; if only limited by temperature resistance, PA46 will also work.

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