关于哪些原因会导致树脂结晶

longjiang23

Crystallization of Liquid Epoxy Resins
Crystallization
Epoxy resins, under certain conditions, can become solid or have a slush like appearance. This
is called crystallization and it is where some component parts of the epoxy resin form a crystal
like structure.
The crystallization of an epoxy is very similar to water freezing in that it goes from a liquid
state to become a solid. And like water once warmed it will revert back to it liquid state without
any change or damage to the properties of the resin. But unlike water which melts at approximately
0°C the melting point of the Epoxy is 50°C.
How to tell if your resin is affected.
The first signs of crystallization are that the resin becomes cloudy, hazy or milky which are
more easily seen in clear resin systems like the Ampreg 21. This opacity is generated by small
crystals free floating in the resin. But as the size of the crystals increases the resin becomes
more like a slush in that the material will still flow but sluggishly. As this crystallization of the
resin increases the slush forms larger lumps.
As the density of the crystallized resin is higher than the material surrounding it sinks to the
bottom of the container, building in thickness until the whole container becomes solid.
Why has this happened?
First, it will not always happen but some things make it more likely to occur.
Viscosity
Lower viscosity systems are more likely to crystallize as the material can flow into the matrix
patterns required for crystallization.
Purity
The higher the purity of the resin increases the possibility as there are less additives to disrupt
the crystalline matrix forming.
Temperature fluctuations
But the main cause of this effect is repeated changes in temperature; the resin being warmed
and cooled repeatedly. The thermal cycling helps to orientate the material into the right chemical
structure for the material to form crystals. But this should be greatly lessened if the material
is stored as directed in the data sheets which normally are between 10°C to 25°C.
The temperature fluctuations that occur between night and day start or enhance the crystal
growth process.
Dust & Contamination
The introduction of dust particles into the resin can accelerate the process as it does give the
crystallisation process a starting point or "seed" from which to start. And once the process is
started it can progress more quickly due to the self organising nature of chemistry.
How to correct the situation
Remember as stated above this process can be reverted with no damage to the resin - just like
melting water, but the temperature involved will be higher.
I this case you will need to heat the resin to a minimum of 50°C and hold it there until it all
completely melts. If any crystals remain, the whole container may become solid again with a
few days. But if the pail/drum is heated to 50°C until ALL of the crystals have melted the resin
will be fine for months if not years if stored correctly.
The point to note is that it is recommended to heat the material for a longer period at 50°C to
ensure complete melting of the crystals and not remove the container too early from the heat.
When heating the crystallised resin the heat will not be transfer quickly and achieving a
consistent bulk resin temperature will take quite some time, possibly even 2-3 days for drums
or IBCs of resin. If the resin is not solid and does flow, it is good practice to mix the material
regularly to ensure even heating.
It is not possible to give an exact time required to completely remove the crystals as it will
depend on the container size, heat source and regularity of mixing but it is better to give the
material longer at 50°C to ensure complete reversal of the resin to it's liquid form. With some
clear resin systems, like the Ampreg 21, it is possible to see when the crystallized material has
melted as the resin will change from cloudy to clear.
Once the material has reverted back to its liquid state it is perfectly suitable for all applications
and should be used as specified in the technical datasheet.
If you have any questions please do not hesitate to contact a member of the Customer or
Technical Support team.

longjiang23

树脂结晶是一种物理现象，通过热或者强力搅拌不影响使用。

tongxuewm

这篇文章应该是中国人写得，翻译成的e文

新鲜人

还是去找中文的吧

红纸鸢

我把楼主的英文翻译出来了，供大家参考：
环氧树脂结晶
环氧树脂，在一定条件下，能形成固体或者表面类似泥浆状。这个状态就叫做结晶，是树脂其中一部分形成晶状结构的过程。
树脂结晶非常类似于水结冰，由液态变为固态的过程。能像冰一样加热后又可以变回原先的液态而不改变其性质。但是不像冰的熔点在约0℃左右，而树脂的熔点是50℃。
如何判断树脂受到影响了呢？
第一个结晶的信号是树脂变得浑浊、有薄雾、像牛奶状，在纯净的树脂里看得更清楚。浑浊是由细小的晶体浮在树脂表面上形成的。但是当晶体增加，树脂看起来更像泥浆，可以流动但是比较粘稠。当树脂中的晶体变成更多的泥浆，会形成结块。
当结晶的树脂液面高于周围的原料时，它会沉到容器的底部，逐渐变厚，最终整个容器内的树脂变成固体。
这是怎么发生的呢？
首先，这不是经常发生的，但是一些参数使其更可能发生。
粘度
低粘度体系更容易结晶，因为原料能流到结晶基体格局中。
纯度
树脂的纯度越高越容易结晶，因为有更少的添加剂干扰结晶基体的形成。
温度变化
最主要的影响因素还是反复变化的温度。树脂重复的加热和冷却。加热有助于原料恢复正常的化学结构从而更有利于结晶。但是如果原料按照数据单指明的储存条件（一般在10℃~25℃）下储存会极大地减小这种可能性。
昼夜温差的波动会加强晶体增长的进度。
灰尘和污染
有灰尘进入树脂会加速晶体化，因为它提供了结晶所需的起点或者叫做“种子”。一旦开始结晶，由于晶体自身的性质和化学性它会进展的更快。
如何解决这个问题
前面所讲这个过程是可逆的，能像冰融化成水一样，但是温度需要高一点。
这个过程你需要加热树脂最少50℃以上，维持温度直到全部融化。如果仍有晶体存在，几天之后整个容器里的原料还会变成固体的。但是如果完全融化后在正确储存的情况下可以存放数月甚至一年。
要注意的一点是在50℃加热树脂的时间长一点，确保晶体完全融化，不要太早地停止加热。当加热的时候不要快速转移，而要得到一个恒定的树脂主体温度，这个过程需要的时间长一点，大概是2~3天/IBC桶。如果树脂不是固态的并可以流动的话，最好加热的时候有规律的混拌一下。
如果不能根据容器大小给出一个能完全融化晶体的准确时间，加热并有规律地混拌，最好停留在50℃的时间长一点来确保树脂完全液体化。一些纯净的树脂体系，例如Ampreg 21，能看见结晶原料的变化，从浑浊变得澄清。
一旦原料恢复到液态，能有很好的使用效果，可以作为技术指标上的规定。
如果你有任何问题请不要犹豫，直接联系客户或技术服务团队的人员。

weiyuzhu

在冬天树脂一般都会结晶，除非这个树脂不是纯的树脂，

越纯洁的树脂越容易结晶

红纸鸢

结晶原因：
1.低粘度体系更容易结晶
2.树脂的纯度越高越容易结晶
3.温度反复变化容易结晶
4.灰尘和污染会加速结晶
解决办法：加热温度在50℃以上，直到树脂全部融化成液态，再储存于规定的温度下。

喇嘛布谷

结晶最常发生在BPA型的环氧树脂里

喇嘛布谷

1、BPA型的环氧树脂在室温下属于过冷液体，虽呈液态，但有天然的结晶化倾向，在较低温度时，倾向更明显。
2、环氧树脂晶体有略微较高的密度，使得晶体缓慢下沉到储存容器的底部，透明的树脂开始出现模糊和浑浊。

caesar09

关于树脂结晶，只要明白晶核的成因即可，晶核分为两类：均相成核与异相成核。晶核是晶体的生长中心。聚合物结晶的晶核尺寸在高分子链方向为7.5~30纳米，在侧向为0.4~2纳米。均相成核是由聚合物因热涨落形成的结晶中心，异相成核是由于某种高熔点异相体的存在使客体的表面形成结晶中心。均相成核的理论解释是基于经典热力学的分析。其基本思想是把成核视为过饱和蒸气或溶质的凝聚。所以也就可以解释为什么气温越低、树脂越纯净越容易结晶。非均相成核的理论是在均相成核经典理论的基础上发展起来的。它能定性地说明在什么条件下外来粒子可以使晶核优先在这里形成，解释了一些结晶现象。