Toughening polyformaldehyde

Larger particles surrounding stress field is greater than the small particles, under the same seed spacing, the stress field of adjacent large particles can be overlapping, thereby achieving brittle ductile transition. And small particles due to the stress field around the weak, so the same spacing to stack, so the material is still fragile. But for toughening impact strength of the resin particle spacing than the particles themselves the greater the influence of particle size on it, only when the seed spacing between particles is less than the critical spacing, injection molding processing materials to brittle transition occurs, the smaller the grain spacing, the shock resistance.

potassium titanate is a white with a range of length to diameter ratio of single crystal fibers. Due to the hardness of low potassium titanate whisker and fiber diameter, the polymer material has good effect and less influence on friction and wear properties, and therefore has set up a file in the engineering plastic composite strengthening is widely used. With potassium titanate whisker to enhance on POM, add alone can make the material tensile strength, rigidity and thermal deformation temperature has a larger increase, but also can make the material has good abrasion resistance and surface smoothness, and other lubricants with added can improve self-lubricating POM grade of strength and rigidity, so it can meet the demand of high friction and wear properties of high strength requirements under the conditions of use.

the POM polarity is small, no reactive groups in the macromolecular, therefore the compatibility with other polymers is the key to the flexibilizer toughening effect. TPU is to find a good toughening agent so far. Generally considered in the process of blending, POM molecules a part of the ether bond formed between the TPU and hydrogen bonds, the hydrogen bond formation is added between the compatilizer. When the TPU content increases from 0 to 30%, the notched impact strength of alloy increases are not obvious, but when the content of TPU content is more than 30%, the impact strength will mutate and rapidly increase with the increase of TPU content, at the same time the tensile strength was decreased.

are many factors that affect elastomer toughening in the process of POM, such as toughening agent structure, particle size and distribution, especially the elastomer and the compatibility of POM in different extent influence of elastomer toughening effect. Elastomer or thermoplastic elastomer toughening role due to the different molecular structure and its size is different also, choose what kind of toughening agent is mainly composed of use requirement to decide. Generally considered flexibilizer, the lower the glass transition temperature, the toughening effect is better.

in toughening agent content is the same situation, grain size and grain spacing, in general, small granularity, grain spacing. Content of toughening agent phase at the same time, different spacing on the toughening of the Izod impact strength. In general elastomer particles in 0. 1 - 0. 3 um can meet the requirements of the toughening. Elastomer particle size and distribution is associated with mixing degree, screw the shearing action of big, system mixing effect will be better, at the same time is closely related with the size of the compatibility of two polymers.

due to the high crystallinity of POM, make its sensitivity, injection molding products processing products easy to residual stress, improving notched impact strength of POM, improve its toughness at low temperature is an important field of POM modification. As impact modifier of POM, there are mainly elastomer and thermoplastic elastomer. Due to poor compatibility of POM and elastomer, so the POM and elastomer blend system are two phase structure, dispersion in POM toughening body continuous phase.

the fracture morphology of impact fracture with sem study showed that pure POM and TPU content lower than 30% of the POM/TPU alloy was brittle fracture, fracture samples show that smooth, TPU particles exposed at the surface, but when the TPU content higher than 30%, the fracture shows that rough, the ductile fracture, with TPU modified POM just improved the toughness of POM at room temperature. Toughening the particle size of body, has important influence on the impact strength of toughening body.

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