Views: 278 Author: Vickey Publish Time: 2023-07-06 Origin: Site
An aromatic diisocyanate is methylene diphenyl diisocyanate (MDI). There are three common isomers: 2,2′-MDI, 2,4′-MDI, and 4,4′-MDI. These are distinguished by the locations of the isocyanate groups around the rings. The most common isomer, commonly known as 4,4′-diphenylmethane diisocyanate, is the 4,4′ isomer.Another name for this isomer is pure MDI. When making polyurethane, MDI interacts with polyols. Polyurethane foam production is the main use for MDI in its commercial form.
MDI has a molecular weight of 250.3 g/mol and the chemical formula C 15 H 10 N 2 O 2. MDI manifests as crystals or a light-yellow fused solid. MDI has an odor threshold of 0.4 ppm. At 25 °C, MDI has a vapor pressure of 5 10-6 mm Hg.
Human sensitivity and asthma may result from acute inhalation of high MDI concentrations. Dermatitis and eczema have been brought on in employees by dermal exposure to MDI. In rabbits, MDI has been seen to irritate the skin and eyes. MDI has been shown to have high to extremely high acute toxicity by inhalation and moderate acute toxicity by oral administration in tests involving acute exposure in rats and mice.
The main contributing factor to occupational asthma is isocyanate exposure. Workers who are exposed to MDI on a regular basis have been shown to develop asthma, dyspnea, and other respiratory impairments. For those who have become sensitive to high levels of MDI over the occupational exposure limit of 20 ppb, some of the effects of MDI may be the result of immune system responses.When exposed to modest doses of MDI, these sensitized people may have negative consequences. Chronically exposed animals have shown respiratory symptoms, such as nasal and lung lesions, consistent with exposure to an irritant.
Based on irritation of the nasal membranes in rats, the Reference Concentration (RfC) for MDI is 0.0006 milligrams per cubic meter (mg/m3). The RfC is a calculation of the continuous inhalation exposure to the human population (along with sensitive subgroups) that is most likely to be free from a significant lifetime risk of adverse noncancer consequences. Instead of serving as a direct risk estimator, it serves as a benchmark for assessing prospective outcomes. The possibility of negative health impacts grows when doses surpass the RfC.Lifetime exposure above the RfC does not imply that an adverse health effect would necessarily occur.
On the impact of MDI on human reproduction or development, there is no information available. In one rat inhalation study, smaller placental and fetal weights as well as more fetuses with different skeletal characteristics were found. Only at the highest dose were these side effects noticed, and they may have been caused by maternal toxicity.
The amount of information available is insufficient to tell if MDI causes cancer in humans. One strain of rats treated with polymeric MDI was observed to have pulmonary adenomas. MDI has been categorized by the EPA as Group D, not classifiable as a human carcinogen.
