A Complete Guide to Ten Major Performance Tests for Plastics | Must-read for Plastic Inspection!

Many people believe that plastic pellets can be qualified simply by checking appearance and grade. However, manufacturers often encounter various production failures. For materials of the same grade, some finished products break easily under bending, some deform at high temperatures, and bubbling or cracking frequently occurs during processing. Most of these problems stem from insufficient key performance tests. Fake modified fillers, substandard molecular weight, falsely marked heat resistance and toughness cannot be identified visually. Only a complete set of performance tests can reveal the true properties of plastics.

This article introduces ten core performance test methods in the plastics industry, applicable for formulation development, raw material selection, incoming inspection and quality review. Suggested for bookmarking.

1. Ash Content Test

What is ash content?
When plastic samples are burned at high temperature, organic polymers are fully combusted and volatilized, and the remaining inorganic residues are ash.

Common residues: inorganic fillers such as calcium carbonate, talcum powder, glass fiber, silica and titanium dioxide.

✅Test Method:

Calcination method. Set the muffle furnace temperature and duration according to plastic types, weigh after calcination to constant weight:
General plastics (PE/PP/ABS): calcined at 600℃ for 2-3 hours to constant weight;
High-temperature engineering plastics such as glass fiber reinforced nylon and PPS: calcined at 750-800℃ to constant weight.
Calculation Formula:
Ash Content (%)=(M₁‑M₀)×100/M
(M: mass of sample; M₁: total mass of ash + crucible; M₀: mass of empty crucible)

✅Core Significance:

Determine the actual filler loading of modified materials and identify adulterated raw materials;
It directly affects material properties: higher ash content → improved rigidity and heat resistance but reduced toughness; lower ash content → better toughness while rigidity and heat resistance decrease.
It is the first step of incoming material inspection. Materials with falsely claimed glass fiber or filler content can be easily detected via ash testing.

2. Moisture Test

Plastic raw materials may look dry, but trace internal moisture can ruin the whole production.
Excessive moisture in raw materials leads to a series of processing defects: surface cracking, abnormal gloss, sharp drop of mechanical properties such as tensile and impact strength. Bubbles and silver streaks during injection molding and extrusion are often caused by excessive moisture rather than equipment faults.

✅Test Significance: Control raw material moisture content, guide drying process and avoid mass scrapping in advance.

3. Melt Flow Index (MFI/MVR)

Melt Flow Index, short as MFI in the industry, directly reflects the melt flowability of plastics.

✅Test Method:

Set specified standard temperature and pressure for the material, extrude melt through a standard die within 10 minutes, divided into mass-based MFI and volume-based MVR.

✅Key Interpretation:

Higher MFI value means better melt flowability.
At the micro level: high MFI corresponds to low melt viscosity and relatively low molecular weight; low MFI corresponds to high viscosity and higher molecular weight.
Selection Tip: Large MFI fluctuation between batches of the same grade indicates unstable molecular weight of raw materials, which easily causes uneven extrusion output and poor consistency of finished products during processing.

4. Tensile & Flexural Test

Tensile and flexural tests are the basic mandatory mechanical tests for plastics, to judge material hardness, strength and bending fracture resistance.

✅Tensile Test

Clamp both ends of standard specimen, apply continuous axial tension until fracture and plot the stress-strain curve.

Interpretation of core parameters:
Elastic Modulus E:
Measure the resistance to elastic deformation. Higher E means harder material; lower E means softer material;
Formula: E=(F / S) /(dL / L)

Yield Strength:
Resistance to obvious plastic deformation of materials;
Tensile Strength:
Maximum tensile stress borne by the specimen before fracture;
Elongation at Break:
Characterizes material toughness. Higher elongation means better tear resistance.
Rule of thumb: Larger σb/σy represents higher material strength; higher elongation at break represents better toughness.

✅Flexural Test

Support the specimen on two fulcrums and apply pressure evenly at the midpoint to observe bending deformation.

Flexural Strength:
Stress borne when the specimen breaks or reaches 5% deformation;
Flexural Modulus:
Represents rigidity. Higher modulus means stronger rigidity; lower modulus means softer material.
Flexural modulus is an essential indicator for selecting shells, brackets and structural parts.

5. Impact Test

The same plastic may not break under slow bending but crack instantly under heavy impact, which is the difference in impact toughness.

✅Test Principle:

Common pendulum impact tests include Charpy and Izod tests. A standard specimen is impacted at high speed. The impact energy consumed per unit cross-sectional area is calculated after specimen fracture to obtain impact strength. Izod notched impact test is the most widely used method for plastic toughness evaluation.
Calculation Formula: E=A/(b·d)
A: total consumed impact energy; b: specimen width; d: specimen thickness
The energy consumed for fracture includes crack initiation, crack propagation, matrix deformation, specimen scattering and mechanical friction loss.

✅Core Significance:

Impact strength refers to the material’s resistance to fracture under high-speed impact. Higher absorbed impact energy means better impact toughness. Many products remain intact at room temperature but break easily at low temperature, essentially due to sharp drop of low-temperature impact strength.

6. Vicat Softening Temperature

A common misunderstanding: Vicat temperature ≠ service temperature, but it is a core heat resistance indicator for quality control.

✅Test Significance

Higher Vicat softening temperature brings better dimensional stability under heat, stronger thermal deformation resistance, higher rigidity and modulus. It is used to compare heat resistance of different materials in incoming inspection and formulation development.

7. Thermal Aging Test

In practical environments, heat and oxygen gradually make plastics brittle, discolored and strength-degraded.

✅Test Principle:

Place standard specimens in a thermal aging chamber, control temperature and air exchange rate for accelerated thermal-oxidative aging.

✅Test Purpose:

Compare property changes such as tensile and impact performance before and after aging to evaluate long-term thermal aging life of materials.

Suitable for evaluating materials for outdoor components and parts working under high-temperature conditions.

8. Viscosity Test

Melt viscosity reflects the internal friction between macromolecules of polymers.

✅Core Rule

Higher viscosity → poorer melt flowability and higher processing difficulty; lower viscosity → easier flow.
For the same polymer system under identical test conditions, melt viscosity is roughly inversely proportional to melt flow index. Viscosity is also an important indicator to indirectly evaluate polymer molecular weight, affected by temperature, pressure and material structure.

9. Combustion Test

Ignition speed, flame spread, smoke generation and dripping of burning plastics are directly related to product safety.

✅Main Test Items

Limiting oxygen index, horizontal burning, vertical burning and glow-wire test.

✅Test Method

Burn standard specimens with specified flame, record afterflame time, burning rate and dripping condition.

✅Industry Value

Flame retardant rating of electronic and electrical appliances and housing parts must be determined by combustion tests, which define the compliance boundary of material application.