The characteristics of EVOH resin

日期:2019/6/5 8:23:23 / 阅读: / 来源:本站

The characteristics of EVOH resin can be summarized as follows
advantage
1 has excellent gas barrier and aroma retention, non-toxic, suitable for food and non-food packaging;
2 with grease resistance and most chemicals, suitable for packaging grease liquids as well as toxic and volatile products;
3 transparency and gloss are good
4 good resistance to UV and other radiation;
5 good mechanical properties, tensile strength and tensile modulus.
Disadvantage
1 is susceptible to moisture, increasing moisture resistance with humidity
2 susceptible to alcohol, strong acids or oxidants
3 tensile properties are limited at low temperatures.
The ethylene content of EVOH is usually 25% to 75%. The ethylene content has a great influence on the oxygen permeability of EVOH. Under low humidity, the lower the ethylene content, the better the barrier property; under high humidity, the barrier property when the ethylene content is 40%. the best
PP/EVOH composite sheets need secondary processing, heat forming, solid phase pressure forming, etc., and EVOH is required to have certain ductility. The intra- and inter-molecular cohesive energy of EVOH is quite large, and the stretching is equivalent when the ethylene content is low. Difficulty, its elongation at break is related to ethylene content
The overmolded container is to be cooked and sterilized at the time of use, and the water absorption of the EVOH is required to be relatively low, and the water absorption of the EVOH decreases as the ethylene content increases.
In summary, in order to meet the barrier requirements of EVOH and improve the tensile and moisture resistance, EVOH with an ethylene content of 38% to -44% should be used.
In addition, when EVOH, adhesive and PP are co-extruded, the melt viscosity must be matched between them. Generally, the melt flow rate of EVOH should be greater than 3g/10min. If the MFR value of EVOH is too low, EVOH, adhesive The melt viscosity between the PP and the PP of the surface layer is difficult to match, resulting in melt wave marks and uneven distribution of layers. Therefore, the EP-H and EP-E grades of EVOH from Japan Kuraray Co., Ltd. can be selected. Chemical E, ET, A, AT grade EVOH
(2) PP. Polypropylene has excellent barrier properties of moisture, good strength, high temperature, light weight, low cost and certain transparency. It is a good material for co-extrusion with EVOH. In order to match the melt viscosity during co-extrusion, PP with a melt flow rate of 15g/10min to 3g10min is generally selected, such as 1300, F401, etc.
(3) Adhesive. PP and EVOH cannot be thermally bonded, and an adhesive must be used between PP and EVOH. The adhesive is based on a polyolefin and is grafted with an acid-based polar group such as maleic anhydride. The bonding mechanism is that the PP layer is entangled with the molecular chain of the PP layer to adhere, and the connection with the EVOH is an adhesive. The polar group forms a chemical bond with an OH group of EVOH. Pay attention when selecting adhesive
1Select adhesive with PP as matrix material
2 should consider the matching of the adhesive viscosity between the adhesive and PP, EVOH;
3 The tensile properties of the adhesive should be considered to avoid delamination during secondary processing.

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