The inner layer of acid-resistant rubber hoses directly contacts acidic media, so strict requirements are placed on the rubber’s density and chemical corrosion resistance. Ordinary acid- and alkali-resistant hoses usually have an inner layer made from natural rubber and styrene-butadiene rubber, and can transport dilute acids at room temperature. Mixing in some reclaimed rubber can effectively reduce material costs. When producing the inner layer of acid-resistant hoses with a mix of natural rubber and styrene-butadiene rubber, how much reclaimed rubber is appropriate? What should be noted when adding reclaimed rubber to the inner layer?
1. Vulcanization formulas for inner layers using natural rubber/styrene-butadiene/reclaimed rubber:
(1) Natural rubber 20 parts, styrene-butadiene rubber 50 parts, reclaimed rubber 30 parts, zinc oxide 3.5 parts, stearic acid 1.5 parts, antioxidant A 1.5 parts, antioxidant D 1 part, paraffin 1 part, carbon black N330 30 parts, kaolin 20 parts, barium sulfate 18 parts, graphite powder 11 parts, asphalt 4 parts, gum rosin 12 parts, accelerator DM 2 parts, accelerator TMTD 1.5 parts; total 207 parts.
(2) Natural rubber 20 parts, styrene-butadiene rubber 50 parts, reclaimed rubber 30 parts, zinc oxide 5 parts, stearic acid 1.5 parts, antioxidant A 1.5 parts, antioxidant D 1 part, paraffin 1 part, carbon black N330 30 parts, barium sulfate 30 parts, asphalt 35 parts, kaolin 25 parts, gum rosin 7 parts, tri-line oil 3.5 parts, accelerator DM 2 parts, accelerator TMTD 1.5 parts; total 244 parts.
(3) Natural rubber 15 parts, styrene-butadiene rubber 45 parts, reclaimed rubber 40 parts, zinc oxide 2.5 parts, stearic acid 1 part, antioxidant A 1 part, antioxidant D 1 part, carbon black N330 30 parts, kaolin 15 parts, barium sulfate 18 parts, heavy oil 2.5 parts, asphalt 4 parts, petroleum resin 9 parts, accelerator DM 1.35 parts, accelerator TMTD 0.15 parts, sulfur 1 part, scorch inhibitor CTP 0.5 parts; total 187 parts.
2. Adjustments when adding reclaimed rubber to natural rubber/styrene-butadiene rubber inner layer formulas:
When adding reclaimed rubber to inner layer formulas primarily made from natural rubber/styrene-butadiene, it’s recommended to use superfine 80-mesh reclaimed rubber similar in properties to the original rubber for better density. Slightly increasing the amount of sulfur (E6LYY39) or accelerators can boost crosslinking and improve corrosion resistance. Use chemically inert fillers like barium sulfate or kaolin, and avoid using materials with poor acid resistance like calcium carbonate. Choose plasticizers that remain stable in acidic or alkaline environments, avoiding easily hydrolyzed ester types.
When adding reclaimed rubber to ordinary acid- and alkali-resistant inner layers, process adjustments for mixing and curing are also needed. It’s recommended to plasticize the reclaimed and original rubbers separately before thorough mixing to ensure uniform dispersion. Pay attention to matching the curing rates of different rubber layers to prevent delamination or surface defects.
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