A comparison of the properties and applications of several biodegradable plastics

The common biodegradable plastics available on the market are listed in the table below, with PLA, PBS and PBAT being the most industrialised. The different biodegradable plastics have different characteristics and each has its own advantages and disadvantages.

In order to promote the understanding and knowledge of biodegradable plastics, I will compare the above biodegradable plastics in terms of comprehensive performance and application areas, with a view to providing reference for those engaged in related industries.

Overall performance comparison

Polyethylene (PE) is a widely used traditional plastic and a major alternative to biodegradable plastics, with excellent crystallinity, water vapour barrier and weather resistance, which can be collectively referred to as 'PE properties'.

In fact, the common biodegradable plastics are basically aliphatic polyesters, such as PLA and PBS, which can be broadly regarded as PE with ester bonds in their molecular chains, giving them their biodegradability and their aliphatic chains their 'PE properties'. Promising biodegradable plastics need to have both biodegradability and 'PE properties'.

It is therefore necessary to compare the overall performance of biodegradable plastics with that of PE.

可以看出，不同可生物降解塑料的特点也不同，各有优缺点，但均不完全具备“ PE 特性”。

PBAT 和PBS 的熔点和力学性能与 PE 相当，说明其可基本覆盖 PE 在一次性制品行业中的应用，但是相比于 PBAT，PBS 存在水解速率过快、贮存稳定性差的缺陷；PLA 的熔点和强度高于 PE，但拉伸韧性和结晶性明显较低，其经过增韧、结晶促进等改性后也可以基本覆盖 PE 在一次性制品行业中的应用。

另外，PLA、PBAT、PBS 的商品化程度较高，在以前供需状况不紧张的情况下，市场价格可稳定在2 万 元／t 左 右，但仍然明显高于通用塑料PE。而且，在现阶段供应不求的情况下，PLA 的市场价格涨至4万元／t，还一料难求。

PGA 和 PHA 的熔点和强度高于 PE，但拉伸韧性低于 PE，具有与 PLA 一样的基本性能特点。但是，它们具有 PLA 所不具备的独特性能，尤其是PGA ，具有非常优异的强度和气体阻隔性，赋予其在高性能塑料领域的应用潜力，如高阻气性包装材料和工程塑料。

现阶段 PGA 和 PHA 的生产成本过高，商品化程度较低，而且降解速率太快，贮存稳定性较差。但是，考虑到其具有独特的性能，且成本在未来有望降低，具有较好的发展前景。

PCL 的熔点仅60℃，使用上限温度低；PPC 为无定型聚合物，且玻璃化转变温度为45℃左右，即 PPC在40℃以上就会发生变形。这两种可生物降解塑料均存在使用上限温度低的缺陷，因此，其应用范围严重受限。

As can be seen, the different biodegradable plastics have different characteristics, each with their own strengths and weaknesses, but none with the full 'PE characteristics'.

The melting point and mechanical properties of PBAT and PBS are comparable to those of PE, indicating that they can basically cover the application of PE in the disposable products industry, but compared to PBAT, PBS has the defects of rapid hydrolysis rate and poor storage stability. The application of disposable products in the industry.

In addition, PLA, PBAT, PBS, a higher degree of commercialisation, in the previous supply and demand situation is not tight, the market price can be stabilised at 20,000 yuan / t left, but still significantly higher than the general plastic PE.

PGA and PHA have a higher melting point and strength than PE, but lower tensile toughness than PE, and have the same basic performance characteristics as PLA. However, they have unique properties that PLA does not have, especially PGA, which has very good strength and gas barrier properties, giving it potential for applications in high performance plastics such as high gas barrier packaging materials and engineering plastics.

At this stage PGAs and PHAs are too expensive to produce, are poorly commercialised, degrade too quickly and have poor storage stability. However, given their unique properties and the prospect of cost reductions in the future, they have good prospects for development.

The melting point of PCL is only 60°C, which is a low upper use temperature; PPC is an amorphous polymer and has a glass transition temperature of around 45°C, meaning that PPC will deform above 40°C. Both of these biodegradable plastics have the disadvantage of having a low upper operating temperature, and therefore their applications are severely limited.

In summary, the market prospects for the already commercialised PLA, PBAT and PBS are good. However, to replace the existing general-purpose plastic PE on a large scale, not only do production costs need to be further reduced, but a number of issues need to be properly addressed, namely improving the "PE characteristics" of the product. In addition, the large-scale application of PGA with its unique properties also needs to be addressed.

Comparison of application areas

Table 4 shows the main applications of some biodegradable plastics at this stage. Among them, PLA and PBAT are mainly used in everyday plastics and are most in line with the current "plastic restriction" policy. According to domestic statistics in 2018, China consumed 20 million tonnes of disposable plastic products, accounting for 33% of domestic plastic production.

Theoretically, PLA and PBAT could replace all disposable plastic products, i.e. a market with a potential volume of over 20 million tonnes.

In addition, the application areas of PLA and PBAT overlap, but their respective characteristics are different, for example, PLA is a hard plastic, while PBAT is a soft plastic, which can be regarded as the PP and PE of petrochemical products, and PLA, which is poorly processed for blown film, is often blended with PBAT, which is tough and can improve the processability of blown film without compromising its biodegradability.

Several other biodegradable plastics that are not at a high level of industrialisation at this stage are basically used in the field of biomedical materials with low usage and high added value. However, as mentioned above, these plastics have unique properties that PLA and PBAT and PBS do not have, and their unique and relevant properties will give them a broad application prospect once the industrialisation process is accelerated.

Conclusion

With the gradual escalation of mandatory waste separation and "plastic restriction" worldwide, biodegradable plastics have taken the limelight, especially in the recent past, the price of PLA, which has the highest market share in biodegradable plastics, has skyrocketed and even become "hard to find". The price of PLA, which has the highest share of the biodegradable plastics market, has recently soared, and even become hard to find.

The annual production capacity of biodegradable plastics in China is about 310,000 tonnes, accounting for 37% of the global annual production of biodegradable plastics. It is predicted that the global annual growth rate of degradable materials will exceed 20%, and China will be the main force for capacity expansion in the coming years, not only to expand exports, but also to contribute to the development of the growing domestic degradable plastics market.

At present, PLA, PBS and PBAT are the most widely produced degradable plastics with high market recognition, and are expected to replace the existing non-degradable plastics PE and PP on a large scale for disposable plastic products.

Other biodegradable plastics have limited production capacity and are concentrated in the high-end biomedical materials with high added value, and are not yet able to compete with PLA and PBS and PBAT in replacing general purpose plastics. However, the large-scale industrialisation of these biodegradable plastics with unique properties is accelerating and is expected to have a promising future.

Disclaimer: This article is from other media and does not represent the views or position of this website. (Content reprinted from: China Plastics Online)
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