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Factors that influence the barrier performance of plastic films

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Factors that influence the barrier performance of plastic films

Plastic films are widely used in packaging, such as food packaging, medicine packaging, electronic items packging etc, so it enable magnificent meaning for the barrier ability of the films. Get deep into the barrier performance of film, and figure out the factors that influence this ability is very important. When we improve the barrier performance, we will directly understand how to improve the actual packaging.

Besides the size of the gas Molecular, the ingredients of the plastic film, the Molecular structure, and the Molecular focusing state, the compatibility between the plastic and the transmission substances, all these factors have some extent of influences on the barrier ability. Below, I am going to describe and analyze on the main factors.

1)Molecular Polarity

When the crystallinity is assigned, the large polar Moleculars or the large extra-strong polar Moleculars are closely combined with each other that cause it difficult for the gas Molecular to transmit. The more polar of the Molecular, the transmission rate is lower, so the barrier performance is better. Among the common used plastic resins, PET and PVA are strong polarity, PA and PVC are polar resin, PS is weak polar, however, PE and PP are non polar resins. The barrier performance is improved along with the Molecular polarity. The Oxygen transmission rates of PET and PE differ much from each other.

Water vapor is polar Molecular. Based on the principle of Like dissolves, the transmission rate and diffusion rate of the water vapor in polar plastic Molecular are both larger than the ones of non polar plastic Molecular.

2)Molecular crystallinity

The required diffusion engery of gas and water vapor Molecular through crystal plastic films is larger than the one through non crystal plastic films, so the transmission rate is lower, so the crystal plastic films show better barrier ability. When the other conditions are assigned and certain, the higher the degree of plastic film crystallinity, the better the barrier performance.

3)Molecular orientation

When the plastic film is stretched and orientated to make it into forms, the plastic molecular are oriented in some kind of extent under the certain press, so the layout is somewhat clear and neat,and close to each other, so the barrier performance improved. The higher the degree of orientation, the better the barrier performance. Esepcially under biorientation,, the size of crystalline grain lowers, at the same time, the crystallinity degree improves.

4)Molecular hydrophilic

Among the plastic films that own hydrophilic performance, PVA and PA film stand out. Hydrophilic resins swells when touched with water because of its hydrophilic ability, so distance between molecular increases and then further cause the decrease of barrier performance. In common situation, the transmission of water vapor transmission rate through hydrophilic plastic films are not constant, it changes along with the concentration of water vapor, so the moisture barrier performance changes, however the water vapor transmission rate through non hydrophilic plastic films are seldom influenced by the concentration of water vapor and ambient moisture.

5)Ambient temperature

Temperature has great influence on the molecular structure of plastic films. When the temperature increases, the orientation of the molecular reduces, the distance between molecular increases, so the barrier performance reduces.

The other transmission rate of the plastic film changes along with the temperature change. In contrast, the gas barrier performance of PVDC film is less influenced by the temperature, aluminum foil is even less influenced by temperature. So these two items are best suitable to be choosed to make high temperature retort pouch.Silicon dioxide deposited film is also less influenced by temperature.

During the actual application, EVOH, PVDC polymer, PAN polyer, PA, PEN, PET are selected as barrier materials, among them, EVOH, PVDC, PAN polymer, and Nylon MXD6 are considered as high barrier material, however PA, PE are considered average barrier materials. Even though the barrier performance of EVOH, PVDC, PEN, PAN are excellent, they are common used in blending, lamination or coating because of some other factors, such as difficult processability, high price, or not good multifunction.

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