Physical Address
304 North Cardinal St.
Dorchester Center, MA 02124
D1644-01 – Standard Test Method Technical Guide
ASTM D1644‑01 (Reapproved 2023) establishes standard test methods for determining the nonvolatile content of varnishes. The nonvolatile fraction represents the material that remains after the volatile solvents are driven off under controlled heat. This measurement serves as an approximate indicator of the film‑forming matter available in the varnish and is a critical parameter for both producers and users to ensure consistent product quality and performance. All values are stated in SI units.
🧪 Scope and Significance
These test methods are specifically applicable to varnishes and are widely used for quality control. By measuring the weight of the residue after a standardized heating process, the nonvolatile content is determined. The standard notes that while this is a useful measure, it may not always perfectly correlate with the exact amount of film‑forming solids, as results can be influenced by oxygen absorption or incomplete solvent removal under specific conditions.
⚙️ Test Method A — Procedure and Parameters
This method specifies a heating schedule of 3 hours at 105 °C ± 2 °C. A thoroughly mixed sample is placed in a stoppered bottle or a weighing pipet. A portion of 1.2 g ± 0.1 g is weighed by difference into a tared, flat‑bottomed dish. The dish should be made of metal or glass, with a diameter between 80 mm and 100 mm and a depth of 5 mm to 10 mm. The specimen is spread evenly by gentle tilting and heated in a ventilated oven. After heating, the dish is cooled in a desiccator and weighed.
💡 Tip: Dish Selection
The term “tared, flat‑bottomed dish” implies that the empty dish must not exhibit a measurable weight change when subjected to the identical heating schedule. Suitable vessels include friction‑top can covers, ointment boxes, or Petri dishes. If a weight change is observed, a more suitable dish must be found, or corrections must be applied.
| 🟦 Parameter | 📏 Specification |
|---|---|
| 🧪 Sample Mass | 1.2 g ± 0.1 g |
| 📐 Dish Diameter | 80 mm – 100 mm |
| 📐 Dish Depth | 5 mm – 10 mm |
| 🌡️ Oven Temperature | 105 °C ± 2 °C |
| ⏱️ Heating Duration | 3 h |
⚠️ Safety Hazard – Flammable Solvents
Since the flash points of many solvents used in coatings are below the test temperature, the lower explosive limits (LEL) of the solvents must not be exceeded. The concentration of solvent vapor in the oven depends on the number of test pans, the percent nonvolatile of the samples, the oven size, the type of convection (mechanical or gravity), and the air exchange rate.
📊 Calculation and Reporting
Calculate the percent nonvolatile matter (NV) using the formula below. Report the result to the nearest 0.1 %.
NV = [(C – A) / S] × 100
| 📌 Symbol | ⚡ Definition |
|---|---|
| A | Weight of the empty dish (g) |
| S | Weight of the specimen used (g) |
| C | Weight of dish and contents after heating (g) |
| NV | Nonvolatile matter (%) |
📌 Potential for High Results
Nonvolatile determinations by this test method may give values higher than the actual film‑forming solids. This can occur due to incomplete elimination of volatile matter or, specifically, the absorption of oxygen by oxidizing‑type varnishes during the prolonged heating period.
❓ Frequently Asked Questions
🔍 What is the primary purpose of ASTM D1644?
Its purpose is to determine the nonvolatile fraction of a varnish by driving off the volatile solvents at a controlled temperature (105 °C ± 2 °C), providing an approximate measure of the film‑forming matter in the sample.
💡 What are the exact specimen mass and dish specifications for Test Method A?
The test requires a 1.2 g ± 0.1 g specimen placed in a tared, flat‑bottomed metal or glass dish. The dish must be 80 mm to 100 mm in diameter and 5 mm to 10 mm in depth.
⚡ What are the specific time and temperature conditions for Test Method A?
The specimen must be heated in a ventilated oven maintained at 105 °C ± 2 °C for exactly 3 hours.
📌 Why might the nonvolatile content results be higher than expected?
High results can arise from incomplete elimination of volatile matter. Additionally, for oxidizing‑type varnishes, oxygen absorption during the 3‑hour heating period can increase the final mass of the residue, leading to an inflated nonvolatile percentage.