PVC toughness and rigidity, do you really understand?
Often hear or see friends on how to test the stand or fall of PVC pipe for the issue of red-faced, others said stepping on cracks is good, some say not shattered is good, some said the light pressure or impact resistance is not comprehensive, plastic toughness and rigidity are opposing concepts. In mechanics, there are two physical quantities of rigidity and flexibility. “Stiffness” is the magnitude of the force required for the deformation of an object. “Flexibility” refers to the deformation of the object under unit force. It can be seen that the larger the “stiffness”, the less prone to deformation (the elongation is small); The more flexible the object is, the more likely it is to deform (the elongation is greater).
In an ideal state, the stiffness of an object tends to infinity (or the force of an object is so small that it can be ignored). We call this object a rigid body. In mechanical analysis, it is possible to ignore its own deformation. Therefore, rigidity is a property that reflects the degree of deformation of objects.
The ductile material is soft, the tensile breaking elongation of the physical meter and the impact strength are greater. Hardness, tensile strength and tensile modulus are relatively small. The rigidity and tensile strength of rigid materials are larger. Fracture elongation and impact strength may be lower; The tensile modulus of elasticity is greater. The rigidity of the flexural strength reaction material is rigid and the material is rigid and the other is ductile. In the ASTM D790 bending performance standard test method, these test methods are suitable for rigid materials and semi-rigid materials. It is not said to be suitable for ductile material, so a resilient elastomer is not tested for bending strength.
Rigidity and brittleness are usually linked together. Brittleness means that when the external force reaches a certain limit, the material is suddenly destroyed without warning, and there is no obvious plastic deformation. The mechanical properties of brittle materials are characterized by far greater compressive strength than tensile strength. Brick, stone, ceramics, glass, concrete, cast iron and so on are brittle materials. Compared with the ductile materials, they are quite unfavorable to the impact load and the vibration.
As engineering plastics, we hope that it will also have good toughness and rigidity. In improving the toughness of materials, it is also necessary to improve rigidity. Generally adding elastomer can increase toughness, adding inorganic filler can increase rigidity. The most effective method is to combine the toughening of the elastomer with the reinforcement of the filler. Poor impact resistance is a performance defect of some important plastics in industry. Such as PVC, PS, PP, etc., especially in low temperature due to its low impact performance, the application is limited.
In thermoplastic plastic, the impact modifier can be greatly improved by adding “impact modifier”. A wide variety of impact modifier, commonly used have ACR – acrylate resin, MBS – – butadiene – styrene copolymer of methyl methacrylate, CPE, chlorinated polyethylene, ABS, EVA, EPT – three yuan 3-20, etc. According to the modification effect of plastic products, the ACR is one of the best comprehensive properties. MBS is an important impact modifier for transparent products, which plays an important role in the global impact modifier market. The impact modifier can improve the impact strength, but has adverse effect on other mechanical strength. If MBS is added to PVC, the tensile strength and bending strength decrease. ACR’s addition also makes the tensile strength, hardness and vica heat resistance of HPVC- high molecular weight PVC decrease. The addition of CPE also reduced the tensile strength, bending strength and wiper softening point of blends. Therefore, when the impact modifier is used, other performance must be taken into account to determine the appropriate dosage.
(Statement: this article is from the network, just for study exchange, no commercial purpose)
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