Why does the PVC discharge hose harden and turn yellow after using it for a long time?

  • Categories:Industry News
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  • Time of issue:2021-06-03
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(Summary description)PVC discharge hose is made of PVC plastic added with plasticizer and other auxiliary materials. The amount of plasticizer is large, and it will be relatively soft when it is first produced. The weather resistance of PVC discharge hose material is not good. In daily use, the color will gradually change due to aging. First, it will turn yellow and then further black.

Why does the PVC discharge hose harden and turn yellow after using it for a long time?

(Summary description)PVC discharge hose is made of PVC plastic added with plasticizer and other auxiliary materials. The amount of plasticizer is large, and it will be relatively soft when it is first produced. The weather resistance of PVC discharge hose material is not good. In daily use, the color will gradually change due to aging. First, it will turn yellow and then further black.

  • Categories:Industry News
  • Author:
  • Origin:
  • Time of issue:2021-06-03
  • Views:0
Information

PVC discharge hose is made of PVC plastic added with plasticizer and other auxiliary materials. The amount of plasticizer is large, and it will be relatively soft when it is first produced. The weather resistance of PVC discharge hose material is not good. In daily use, the color will gradually change due to aging. First, it will turn yellow and then further black.

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The main reason why PVC discharge hose turns yellow is the following:
(1) Because PVC resin is a kind of heat-sensitive plastic, its light stability is poor. Under the action of heat and light, the branched chain will undergo de-HCI reaction and polyene structure molecules. When the number of conjugated double bonds in the main chain is not too much, it will be produced. With slight chromatic aberration, hydrogen chloride will first react with the surrounding potential acid-reactive substances, and its conjugated double bond becomes a new active site in the PVC molecular chain. After being triggered by light into macromolecular free radicals, PVC is easily oxidized and produced Discoloration.
(2) There are a certain amount of low molecular weight components in the PVC resin in the PVC discharge hose, which reduces the thermal stability of the polymer. The mechanism of PVC decomposition includes free radical mechanism, ionic mechanism, and single molecule mechanism. In addition to the stabilizer, it may be affected by the quality of the PVC resin itself, such as whether there is too much residual initiator in the PVC resin.
(3) If there are certain impurities in the polymer in the PVC discharge hose, for example, the initiator, catalyst, acid and alkali added during the polymerization process cannot be removed completely, or it absorbs water during storage and transportation, it will reduce the polymer. The stability. Because these substances can cause molecular-ion degradation reactions, CPE contains more low-molecular substances such as Cl2 and HCl, which can easily accelerate the thermal decomposition of the resin. Therefore, for the poorly stable PVC CPE system, the yellowing problem of some profiles can also be eliminated by increasing the amount of stabilizer.
(4) Rigid PVC structural profile, which is a mixed system composed of polyphase polymer with PVC as continuous phase and mixture kneading heat stabilizer, light stabilizer lubricant, filler and pigment. When PVC profile is exposed to natural environment When the PVC component is dehydrochlorinated, the original calcium carbonate component will be converted into a new calcium chloride component, which is dispersed in the oxidative degradation product layer and forms potential water absorption sites, which is one of the reasons for the yellowing of outdoor profiles .
(5) In addition to temperature and stress, the PVC discharge hose is subjected to shear stress and tensile stress during high agitation, cold agitation, extrusion, etc., before it is molded, which causes thermal degradation.

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