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<\/div>\n<\/div>\n <\/div><\/div>\n\n\n\nThe first action is called downward reduction.<\/h3>\n\n\n\n
In other words, when you see any macro-level conclusion, don’t rush to accept it, but keep asking questions:<\/p>\n\n\n\n
Why is this happening?<\/p>\n\n\n\n
Keep asking until you can’t push it any further and have to stop at one point.<\/p>\n\n\n\n
At the most basic level, that’s true. But here’s the key point: you can’t stop at industry conventions.<\/p>\n\n\n\n
Many people think they are doing first-principles analysis, but It’s just that it stopped too early.<\/p>\n\n\n\n
For example:<\/p>\n\n\n\n
- \n
- “Everyone chooses this material.”<\/li>\n<\/ul>\n\n\n\n
- \n
- That’s what it says in the manual.<\/li>\n<\/ul>\n\n\n\n
- \n
- “That’s how we’ve done projects before.”<\/li>\n<\/ul>\n\n\n\n
- \n
- “The supplier recommends this brand.”<\/li>\n<\/ul>\n\n\n\n
These are not first principles; they are merely industry practices.<\/p>\n\n\n\n
Experience, engineering practices, and historical paths.<\/p>\n\n\n\n
They may be useful, but they are not the underlying cause.<\/p>\n\n\n\n
The true stopping point should be placed at a more fundamental level, such as conservation laws, thermodynamic laws, structure-property relationships, or the actual microscopic phenomena within the material mechanism.<\/p>\n\n\n\n
Therefore, the dividing line between first principles and ordinary analysis lies not in whether you ask “why,” but in your final floor to stop at.<\/p>\n\n\n\n
If you stop at “everyone does it this way,” then you’re still just relying on experience points.<\/p>\n\n\n\n
You only truly understand it when you stop at “this structure determines this performance”.<\/p>\n\n\n\n
Really getting to the bottom of it.<\/p>\n\n\n\n
The second action is called upward reconstruction.<\/h3>\n\n\n\n
Downward reduction simply breaks the problem down to its lowest level, but that’s still not enough.<\/p>\n\n\n\n
What truly matters is: can you take these fundamental principles, combine them with the real constraints you have at your disposal, and then launch a plan?<\/p>\n\n\n\n
Note that this is not a matter of simply applying conclusions that have already been derived by others.<\/p>\n\n\n\n
Just because someone else uses this brand name doesn’t mean you should use it too.<\/p>\n\n\n\n
Just because someone else emphasizes this parameter doesn’t mean that parameter is your core contradiction.<\/p>\n\n\n\n
Just because someone advertises a selling point doesn’t mean the customer will actually buy it.<\/p>\n\n\n\n
That’s the selling point.<\/p>\n\n\n\n
Downward reduction simply involves listing the rooms one by one.<\/p>\n\n\n\n
Rebuilding upwards is the only way to reconnect these rooms into a single line.<\/p>\n\n\n\n
A walkable corridor.<\/p>\n\n\n\n
True judgment grows in this “corridor”.<\/p>\n\n\n\n
This method is particularly useful in polymer materials.<\/p>\n\n\n\n
Because the vast majority of macroscopic performance can ultimately be attributed to lower performance.<\/p>\n\n\n\n
Make an appointment on the third floor:<\/p>\n\n\n\n
Chain structure, phase state, molecular motion.<\/h2>\n\n\n\n
- \n
- Why is the material strong?<\/li>\n<\/ul>\n\n\n\n
- \n
- Why is the material soft?<\/li>\n<\/ul>\n\n\n\n
- \n
- Why do materials absorb water?<\/li>\n<\/ul>\n\n\n\n
- \n
- Why is the material heat-resistant?<\/li>\n<\/ul>\n\n\n\n
- \n
- Why do materials age?<\/li>\n<\/ul>\n\n\n\n
- \n
- Why does the material crack?<\/li>\n<\/ul>\n\n\n\n
As you follow the trail, most of them eventually come down to these three questions.<\/h3>\n\n\n\n
- \n
- Which type of chemical bond is at play?<\/li>\n<\/ul>\n\n\n\n
- \n
- Which chain structure determines it?<\/li>\n<\/ul>\n\n\n\n
- \n
- What phase is limiting it?<\/li>\n<\/ul>\n\n\n\n
- \n
- What scale of molecular motion controls it?<\/li>\n<\/ul>\n\n\n\n
Therefore, the first consideration in polymer science, to be more specific…<\/p>\n\n\n\n
It means tracing any performance metric all the way back to the “link”.<\/p>\n\n\n\n
The three layers of “structure-phase-molecular motion” are then discussed, and from there…<\/p>\n\n\n\n
Push back the project plan.<\/p>\n\n\n\n
The following example of nylon absorbing water will illustrate this point.<\/p>\n\n\n\n
Why does nylon absorb water? The key isn’t the brand name, but the acyl group.<\/p>\n\n\n\n
Amine Density.<\/p>\n\n\n\n
The common analogy approach is:<\/p>\n\n\n\n
PA6 is absorbent, and its dimensions are unstable, so I’ll find an absorbent…<\/p>\n\n\n\n
Choose a brand with a lower water content, or add some fiberglass, and adjust the size accordingly.<\/p>\n\n\n\n
Press down on the change in size.<\/p>\n\n\n\n
This can certainly solve some problems, but it’s only based on experience.<\/p>\n\n\n\n
Replacement, not underlying derivation.<\/p>\n\n\n\n
What we are really asking is:<\/p>\n\n\n\n
Why does PA6 absorb water?<\/p>\n\n\n\n
Because nylon molecules contain a large number of amide bonds, that is<\/p>\n\n\n\n
\u2014CONH\u2014 structure. This structure has a strong hydrogen content.<\/p>\n\n\n\n
The bonding site makes it easy for water molecules to form an interaction.<\/p>\n\n\n\n
use.<\/p>\n\n\n\n
Once water enters, it will disrupt the original interchain hydrogen bond network.<\/p>\n\n\n\n
Network. On the one hand, it reduces the interaction between molecular chains.<\/p>\n\n\n\n
On the one hand, it is weak and acts as a plasticizer; on the other hand, it stretches…<\/p>\n\n\n\n
Interchain distance leads to swelling and dimensional changes.<\/p>\n\n\n\n
Go down one more layer:<\/h2>\n\n\n\n
What does water absorption capacity essentially depend on?<\/h3>\n\n\n\n
It largely depends on the amide groups per unit chain length density.<\/p>\n\n\n\n
The denser the amide groups, the more sites water can bind to, and the better the adsorption capacity.<\/p>\n\n\n\n
The stronger the water absorption tendency, the less water-absorbing the amide group; the rarer the amide group, the stronger the water absorption tendency.<\/p>\n\n\n\n
The weaker.<\/p>\n\n\n\n
This is no longer a “brand name issue,” but a “chain structure question”.<\/p>\n\n\n\n
Therefore, you can determine the general direction without consulting a table:<\/p>\n\n\n\n
- \n
- PA6 has a high amide density; therefore, it has a high water absorption rate;<\/li>\n<\/ul>\n\n\n\n
- \n
- PA612 has a longer carbon chain, resulting in a lower amide density.The water absorption rate is significantly reduced;<\/li>\n<\/ul>\n\n\n\n
- \n
- The long methylene chain of PA12 further dilutes the amide group.<\/li>\n<\/ul>\n\n\n\n
It is compacted, so its water absorption rate is lower.<\/p>\n\n\n\n
Under typical conditions, the saturated water absorption rate of PA6 can reach 9%.<\/p>\n\n\n\n
PA612 decreased to approximately 3%, while PA12 could decrease.<\/p>\n\n\n\n
It’s in the range of 1% to 2%.<\/p>\n\n\n\n
This order wasn’t derived by memorizing data, but rather…<\/p>\n\n\n\n
Deduced from the amide density.<\/p>\n\n\n\n
This is downward reduction.<\/p>\n\n\n\n
How to rebuild upward?<\/h2>\n\n\n\n
If your ultimate goal is “wet-state dimensional stability”, then positive leverage shouldn’t just be about “finding a low-absorption brand”.<\/p>\n\n\n\n
Instead of referring to the “number”, we need to return to two directions:<\/p>\n\n\n\n
- \n
- First, reduce the density of the amide adhesive;<\/li>\n<\/ul>\n\n\n\n
- \n
- Second, it reduces the ability of water molecules to approach amide groups.<\/li>\n<\/ul>\n\n\n\n
Following this logic, you would naturally deduce the long carbon chain nylon.<\/p>\n\n\n\n
For example, PA1010, PA12; or push to a semi-aromatic formula.<\/p>\n\n\n\n
Nylon, such as PPA and PA6T systems.<\/p>\n\n\n\n
Why?<\/p>\n\n\n\n
Because long carbon chains can dilute the density of amides and reduce water absorption driving force.<\/p>\n\n\n\n
The introduction of the aromatic ring, on the one hand, dilutes the amide group.<\/p>\n\n\n\n
On the one hand, the group increases the rigidity of the chain segment, and on the other hand, it can also improve…<\/p>\n\n\n\n
Heat resistance and HDT.<\/p>\n\n\n\n
At this point, when you choose materials, it’s no longer about “heard this brand absorbs…”<\/p>\n\n\n\n
It’s not about “low water absorption,” but about understanding why it has low water absorption, understanding its…<\/p>\n\n\n\n
Which underlying contradiction is being resolved?<\/p>\n\n\n\n
Conversely, is adding fiberglass useful?<\/p>\n\n\n\n
It’s useful, but it solves a different problem.<\/p>\n\n\n\n
Fiberglass can reduce the absolute dimensional changes of materials after absorbing water.<\/p>\n\n\n\n
Value, because it is equivalent to adding rigidity to the system.<\/p>\n\n\n\n
The skeleton constrains expansion.<\/p>\n\n\n\n
However, fiberglass does not eliminate the driving force that drives nylon to absorb water.<\/p>\n\n\n\n
Water will still get in, and the hydrogen bond network will still be disrupted.<\/p>\n\n\n\n
The matrix will still be plasticized, so wet strength and modulus…<\/p>\n\n\n\n
The quantity and fatigue performance may still decline.<\/p>\n\n\n\n
Therefore, checking the license plate number only stops at this point.<\/p>\n\n\n\n
Tracing the chain structure backward from the amide density is the real key to solving the problem.<\/p>\n\n\n\n
Connect the questions.<\/p>\n\n\n\n
This is the value of first principles:<\/p>\n\n\n\n
It’s not telling you “PA12 is more water-resistant than PA6”, but rather telling you why it’s more water-resistant; it’s not about making you remember more.<\/p>\n\n\n\n
It doesn’t just give you a conclusion about the material, but rather empowers you to re-derive the material. The ability to choose ColorOS Notes<\/p>\n\n\n\n
![\"One](\"https:\/\/www.sheenmaterials.com\/wp-content\/uploads\/2026\/06\/One-of-Sheen-Materials-production-workshops-1-scaled.webp\")
<\/div>\n\n\n\n<\/p>","protected":false},"excerpt":{"rendered":"
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- Second, it reduces the ability of water molecules to approach amide groups.<\/li>\n<\/ul>\n\n\n\n
- First, reduce the density of the amide adhesive;<\/li>\n<\/ul>\n\n\n\n
- The long methylene chain of PA12 further dilutes the amide group.<\/li>\n<\/ul>\n\n\n\n
- PA612 has a longer carbon chain, resulting in a lower amide density.The water absorption rate is significantly reduced;<\/li>\n<\/ul>\n\n\n\n
- PA6 has a high amide density; therefore, it has a high water absorption rate;<\/li>\n<\/ul>\n\n\n\n
- What scale of molecular motion controls it?<\/li>\n<\/ul>\n\n\n\n
- What phase is limiting it?<\/li>\n<\/ul>\n\n\n\n
- Which chain structure determines it?<\/li>\n<\/ul>\n\n\n\n
- Which type of chemical bond is at play?<\/li>\n<\/ul>\n\n\n\n
- Why does the material crack?<\/li>\n<\/ul>\n\n\n\n
- Why do materials age?<\/li>\n<\/ul>\n\n\n\n
- Why is the material heat-resistant?<\/li>\n<\/ul>\n\n\n\n
- Why do materials absorb water?<\/li>\n<\/ul>\n\n\n\n
- Why is the material soft?<\/li>\n<\/ul>\n\n\n\n
- Why is the material strong?<\/li>\n<\/ul>\n\n\n\n
- “The supplier recommends this brand.”<\/li>\n<\/ul>\n\n\n\n
- “That’s how we’ve done projects before.”<\/li>\n<\/ul>\n\n\n\n
- That’s what it says in the manual.<\/li>\n<\/ul>\n\n\n\n