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Design Considerations for Flexible Intermediate Bulk Containers (FIBCs)

Release date:

2021-07-14

First, to meet the required safety factor, the base fabric should possess high strength; however, higher strength is not always preferable. Assuming a specific basis weight, this holds true under the general principle that tensile strength and elongation are inversely related.

First, to meet safety requirements, the base fabric should possess high tensile strength; however, higher strength is not always preferable. Assuming a given basis weight, and in accordance with the general principle that tensile strength and elongation are inversely related, the flat filaments used for weaving must strike a balance: while maximizing tensile strength, they should also maintain adequate elongation. Without sufficient elongation, an excessive focus on tensile strength can be counterproductive, leading to a significant deterioration in the material’s aging performance. Even without the addition of processing aids, elongation remains one of the key indicators for assessing fabric performance. Once the base fabric’s strength has been designed and specified, the sum of the individual filament tensions across the intended width will not equal the measured tensile strength of the fabric; a weaving loss of 5% to 15% is typically observed. This loss is influenced by factors such as equipment configuration and its age, as well as by the melt index (indicating the material’s softness or hardness), the formulation ratio, and the specific manufacturing process. Additionally, the weft direction generally exhibits a greater loss of strength compared to the warp direction.

Secondly, the production of bulk bags must strictly prohibit the addition of recycled materials, as this poses significant safety concerns. While polypropylene boasts good mechanical properties, its resistance to natural aging is inherently poor. To maintain relatively long‑term performance, the judicious and scientifically sound incorporation of additives is essential. Using recycled materials, on the one hand, makes it difficult to control the material composition and predict the final product’s performance; on the other hand, repeated or even multiple thermal reprocessing of the polymer chain can render even the most effective “anti‑aging agents” unreliable in delivering consistent results.

Third, resistance to natural aging is a niche discipline involving multiple theories and complex underlying mechanisms; many researchers have only scratched the surface. Nevertheless, regarding the anti‑aging performance of plastic‑woven products, the journal China Plastics, in its 1998 Issue No. 7, published an article titled “Preliminary Exploration of the Natural Aging Resistance of Polypropylene Fabrics,” which examined both the relevant mechanisms and the observed effects. The main conclusions were:

1. There is a significant difference in performance between fabrics formulated with an anti‑aging agent and those without one.

2. In China, several brands of raw materials exhibit relatively superior performance compared to standard grades, even when no additives are used.

3. Adding additives to the raw materials is crucial; it requires thorough mixing while ensuring that the additives can enter the料筒.

4. The dosage of additives must be appropriate: too little will result in insufficient effectiveness, while too much is wasteful.

5. The stabilizer grade must be appropriate. The wavelength that the additive is intended to block should correspond to the sensitivity range of all raw materials.

6. Determine an appropriate drawing ratio that, while meeting strength requirements, maintains sufficient elongation and ensures its consistency.

7. When the finished fabric is relatively thick, the loss in performance is relatively small.

8. Coated films exhibit superior aging resistance compared to uncoated films, with PE films outperforming PP films.

9. Products with smooth surfaces are superior to those with wrinkled surfaces.

10. A higher elongation (when appropriate) is preferable to a lower one.

11. The tensile strength of fibrillated flat yarn is lower than that of non‑fibrillated yarn.

12. The product’s aging resistance shall be determined in accordance with the climatic characteristics of the region of use.

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Design Considerations for Flexible Intermediate Bulk Containers (FIBCs)

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