Startex Isopropanol, Isopropyl Alcohol IPA-99% is propan-2-ol, chemical formula (CH₃)₂CHOH, registered under CAS 67-63-0 and EC 200-661-7, and supplied at a nominal minimum purity of 99.0% by GC area. The material is an anhydrous technical solvent, not a diluted aqueous blend. At 101.3 kPa, the saturated boiling point is 82.5 °C; the closed-cup flash point is 12 °C. Vapour pressure at 20 °C is 4.4 kPa, the lower and upper flammability limits in air are approximately 2.0 vol% and 12.7 vol%, and the autoignition temperature is 399 °C. Liquid density is 0.786 g/cm³ at 20 °C, viscosity is 2.27 mPa·s at 20 °C, and refractive index n₂₀/D is 1.3776.

Because the technical name includes “99%,” the water content is a release parameter. The isopropanol–water system forms a minimum-boiling azeotrope at approximately 87.7 wt% isopropanol and 80.37 °C; production of an anhydrous 99% grade therefore requires drying above the azeotropic limit, such as extractive distillation or molecular-sieve adsorption. Water in delivered lots is measured by Karl Fischer titration using a method aligned to ASTM E203. Startex-specific certificate of analysis values should be obtained for trace residue, acidity, and metal profiles; this webpage does not substitute for batch documentation. The physical property values in this paragraph are standard published solvent data for anhydrous 2-propanol, not unique to a single producer.

What Solvent Parameters Define the 99% Grade Against Diluted Isopropanol Streams?

The 99% grade differs from 70% v/v or 91% v/v aqueous isopropanol primarily in water activity, evaporation rate, and ionic solvation behaviour. At 70% v/v, water reduces the solvent’s ability to wet hydrophobic surfaces and leaves a slower-evaporating film; however, the water fraction increases dielectric constant and improves dissolution of sodium chloride and other ionic flux residues. Standardized ionic cleanliness testing of printed boards according to IPC-TM-650 2.3.25 uses a 75 ± 2 vol% isopropanol–water extract solution, not an anhydrous solvent, because the water component dissolves and transports ionized residues into the test solution. The anhydrous 99% grade is therefore selected when moisture exposure must be minimized, when ultrasonic cavitation and fast drying are required, or when water would hydrolyse a substrate or interfere with subsequent conformal coating adhesion.

Relative to other short-chain alcohols, the polar and hydrogen-bonding contributions define substitution behaviour. Methanol has a higher vapour pressure of 12.8 kPa at 20 °C and stronger polar solubility, but its systemic toxicity restricts use in open cleaning equipment. Ethanol boils at 78.4 °C, slightly lower than isopropanol, but may be subject to potable excise controls and denaturing documentation. n-Propanol has the same molecular weight as isopropanol but a boiling point of 97.2 °C and a flash point near 22 °C; it evaporates more slowly and is not a direct drop-in where high-speed drying is required.

Compared with acetone, IPA-99% is a weaker polar solvent: the polar Hansen parameter of isopropanol is 6.1 MPa^1/2, whereas published data for acetone is approximately 10.4 MPa^1/2. This does not automatically indicate safe use on all plastics. Polycarbonate and acrylic components can still undergo environmental stress cracking under moulded-in stress when exposed to isopropanol. Plastic compatibility must be tested on production parts according to ASTM D543-21 or equivalent immersion protocols. In stencil misprint removal and wiping operations, stainless steel or PTFE wetted parts are preferred; EPDM and natural rubber may swell in isopropanol. Published compatibility data for Startex-specific IPA-99% against particular elastomer grades is limited, so seal selection should be verified with the elastomer supplier using a method such as ISO 1817.

Equipment-Limited Defluxing Conditions for Anhydrous Isopropanol

In printed circuit board defluxing, Startex IPA-99% functions as a rinse solvent for rosin-based flux residues and selected low-residue activator packages. The process temperature is limited by the 12 °C closed-cup flash point before solvency limits are reached. In batch ultrasonic cleaning tanks with 40 kHz transducers, acoustic energy raises bulk liquid temperature during sustained operation. If the tank is open, bulk temperature is maintained below 35 °C using a closed-loop stainless steel chiller or plate heat exchanger rated for flammable liquids. Immersion heaters are not recommended because local skin temperatures can exceed the flash point and create a headspace ignition hazard even when bulk temperature is below the limit. Area classification of the room follows IEC 60079-10-1 or NFPA 30; ventilation must control the headspace concentration relative to the lower flammability limit of 2.0 vol%.

The viscosity of 2.27 mPa·s at 20 °C is low enough to support effective ultrasonic cavitation in 40 kHz tanks; higher-viscosity solvents can damp transducer output and reduce flux removal efficiency. For ionic contamination control, IPC-TM-650 2.3.25 is the reference extraction method, but the extract solution is a 75% isopropanol–water mixture. The anhydrous product is not a substitute for that standard extractant. A final deionized water rinse is used on water-safe assemblies after IPA defluxing to remove any low-volatility residues released from the solder mask or component markings.

In solventborne coating and adhesive adjustment, the product is introduced as a co-solvent or letdown medium for cellulosic resins, acrylic lacquers, and polymethyl methacrylate systems in which a mild hydrogen-bonding alcohol is needed to reduce application viscosity without inducing film blush. The solvent is not suitable for two-component polyurethane systems because the secondary hydroxyl group consumes isocyanate and reduces crosslink density. Formulators using moisture-sensitive alkyd or organotitanate-catalysed chemistries must verify water content on the certificate of analysis; even 0.2 wt% water can be significant where water initiates premature gelation or consumes catalyst. Application viscosity is controlled with a Ford or Zahn cup according to the coating system, with ASTM D1200 or ASTM D4212 used as the laboratory reference method.

Because isopropanol is a secondary alcohol, it also participates in esterification and dehydrogenation. In esterification with acetic acid, isopropyl acetate is produced; in catalytic dehydrogenation, acetone is produced. These are not primary uses for a cleaning-grade solvent but define the reactivity of the hydroxyl group. In formulated mixtures containing acid anhydrides or reactive acid chlorides, slow esterification can generate water and reduce shelf life. Startex IPA-99% should therefore not be stored blended with acids, acid anhydrides, or acid chlorides unless the blend is intentionally designed for reaction and stability data are available for the specific formulation.

When a Formulation Substitutes IPA-99% for n-Butanol in Gravure Ink Dilution

If an ink formulator replaces n-butanol with anhydrous isopropanol in a gravure or flexographic fluid, the driving variables are the lower boiling point of isopropanol, 82.5 °C versus 117.7 °C for n-butanol, and the lower vapour pressure of isopropanol relative to ethanol, 4.4 kPa versus 5.8 kPa at 20 °C. The faster solvent release reduces retained solvent in printed film when drying tunnel airflow is adequate. However, the flash point of isopropanol is 12 °C, compared with 35 °C for n-butanol, so the replacement shifts the printing deck fire area classification and requires interlocks on exhaust air volume. Carbon bed solvent recovery units treating water-miscible solvent exhaust lose adsorption capacity when inlet relative humidity exceeds 60%; moisture displaces organic solvent from activated carbon, and desiccant pre-drying or increased bed capacity is required.

The polar and hydrogen-bonding parameters of isopropanol, δP 6.1 MPa^1/2 and δH 16.4 MPa^1/2, are lower than those of ethanol and methanol, making IPA a milder hydrogen-bonding solvent. This is useful when strong polarity would swell or attack pigment binder resins. However, the shift from n-butanol to IPA changes resin solution stability: in some maleic-modified rosin and polyamide ink systems, n-butanol contributes stronger solvent retention and solvation of high acid number resins; isopropanol may require an added retarder such as butyl glycol or propyl acetate to maintain cell transfer. Published data for Startex-specific ink formulations is limited; press trials with a drawdown bar and ISO 2834 or equivalent proofing method are used to verify print density and mottle.

For analytical use, technical-grade IPA-99% is not automatically equivalent to HPLC-grade or LC-MS-grade isopropanol. If used as a mobile-phase component, the supplier must confirm UV absorbance, non-volatile residue, and trace metal levels against the specific detection wavelength and column chemistry. Technical-grade solvent may contain unspecified low-level aldehydes or ketones that are not relevant in cleaning but can form adducts in derivatization-sensitive methods. Users should require the batch certificate of analysis and retained sample data before substituting Startex IPA-99% into a regulated analytical procedure.

For surface disinfection, the 99% grade is not a direct replacement for 70% v/v or 75% v/v aqueous isopropanol. The presence of water is required to slow evaporation and to support protein denaturation kinetics; anhydrous solvent dries too quickly to achieve the required contact time under common wiping conditions. The 75% v/v final concentration is aligned with the WHO-recommended isopropanol hand-hygiene range, whereas the anhydrous product is used for fast-drying cleaning where water is excluded. Strong oxidizers, concentrated nitric acid, and alkaline hydroxide solutions should be isolated from isopropanol; contamination can generate heat and increase the fire risk associated with the 12 °C flash point. Bulk storage uses grounded and bonded carbon steel or stainless steel tanks under a nitrogen pad to maintain water specification and exclude headspace oxygen. At relative humidity above 60%, atmospheric tank breathing increases water uptake and can bring stored material below the nominal 99% purity; therefore, desiccant vents or a pressure/vacuum valve with nitrogen blanket are specified.