Criteria for Oil-Only Absorbent Skin Design
Oil-only absorbents are composed of two components: skin and filler. The function of the filler material is the bulk of the oil absorption, while the function of the skin is to keep the filler contained and selectively let oil pass through while repelling water (selective permeability and hydrophobicity). The skin material must also be tear-resistant and have the high tensile strength to endure rough handling during operations so the absorbent may be wrung out and reused if it is required by the operator. To counter the fragile nature of non-woven polypropylene fabric, absorbent booms are covered in a nylon mesh to protect the skin. All these properties must be carefully designed to not affect the other while being as cost-effective as possible.
Hydrophobicity and Selective Permeability
Figure 1: Blue Drop (water). Yellow Stain (Oil). Left Image (Green Boom’s Oil-Only Absorbent Skin. Right Image (Green Boom’s Oil-Only Absorbent Skin and Commercial Polypropylene Oil-Only Skin)
If the absorbent skin is not hydrophobic, water may pass through into the filler material, which reduces the oil absorption capacity. Traditionally, non-woven spun-bond polypropylene fabric is used as the skin material due to its natural hydrophobicity and porous structure. However, Green Boom’s skin is made from a completely biodegradable, natural fiber. Previously, cellulosic materials have not been used in this application due to their hydrophilic nature. While some natural fabrics are available with hydrophobic coatings or backing, they are not biodegradable and do not possess the other properties essential for an oil-only absorbent skin.
Green Boom’s fabric is designed starting at the fiber’s surface chemistry and structure, so the resulting material is hydrophobic and remains biodegradable. Then, absorbent skin is created from weaving in a pattern to maximize the selective permeability of oil over water while completely repelling water at the surface.
Skin Strength and Reusability
The skin must have high tensile strength and be tear-resistant so rough handling or wringing out does not tear the skin. An easily torn skin may result in the oil-saturated filler being scattered in the environment, which defeats the purpose of the clean-up operation. The tear strength of the material depends on the fabric weave, structure, fiber material used and density of the resulting fabric. Usually, the skin for oil-only absorbents is a low density (between 30 - 50 GSM) polypropylene (PP) non-woven fabric. While this lends to acceptable oil permeability, low weight and low cost, it also leads to low skin strength. This causes pillow, socks and booms to tear during slight rough handling and are not amenable to wringing and reusing.
Green Boom’s skin materials were designed with this in mind. Unlike non-woven spun-bond PP, Green Boom’s oil-only absorbent skin is a woven fabric resulting in significantly high tensile and tear strengths. Green Boom’s absorbents can be wrung and reused multiple times without any damage.