Ultraviolet (UV) exposure can affect plastic components, so the properties measured immediately after 3D printing may not tell the whole story about how a part will perform after environmental exposure. For engineers selecting materials and designers developing printed products, it matters whether different polymers respond in the same way. A study by Adi Pandžić, PhD, compared the tensile and flexural strength of Fused Deposition Modeling (FDM) specimens made from polycarbonate (PC) and polylactic acid (PLA), before and after controlled UV exposure.
Key findings
- After 24 hours of continuous UV exposure, mean PC tensile strength decreased from 58.500 MPa to 57.560 MPa.
- Mean PLA tensile strength increased from 42.140 MPa to 46.760 MPa after exposure.
- Mean flexural strength increased for both materials: PC rose from 89.956 MPa to 92.986 MPa, and PLA from 77.140 MPa to 87.239 MPa.
- The reported t-tests found statistically significant differences between control and treated groups for both tensile and flexural strength.
- PLA showed a more pronounced response than PC in this experiment, but the findings apply to the tested materials and conditions.
Why test UV effects on 3D-printed materials?
Additive manufacturing builds components by adding material layer by layer. FDM is a widely used 3D printing process in which a filament is deposited in successive layers. A printed component’s performance depends on the polymer and printing conditions, and may also be affected by its environment. UV exposure is one factor worth considering when assessing printed plastics.
It would be unsafe to assume that all polymers respond alike. This study therefore tested PC and PLA separately and measured two mechanical properties. Tensile strength describes a material’s resistance to a pulling force. Flexural strength describes its response to loading that bends it. The study focused on these strength measures rather than attempting to characterize every possible aspect of material aging or component performance.
Materials, printer and test method
The study printed 20 specimens on an Ultimaker S5 3D printer: ten made from PC and ten from PLA. For each material, five specimens formed an unexposed control group and five formed a UV-treated group. All specimens were printed in the flat XY orientation with 100% infill density. Infill is the internal structure that fills a printed part; at 100% density, the specimens were produced as solid structures.
Layer height was 0.15 mm for both materials. PLA was printed at 200 °C, with a build plate temperature of 60 °C, a print speed of 70 mm/s and fan speed of 100%. PC was printed at 280 °C, with a build plate temperature of 110 °C, a print speed of 50 mm/s and fan speed of 0%.
UV exposure followed ISO 4892-3, Method B, with continuous exposure for 24 hours. The chamber temperature was set to 50 °C, and the equipment is identified in the paper as a Formlabs Cure chamber.
The specimens were tested on a Shimadzu AGS-X universal testing machine at a speed of 5 mm/min. The paper says specimen design followed ISO 527-2 for tensile testing and ISO 178 for flexural testing. Its description of the actual tests names ISO 527-1 for tensile and ISO 187 for flexural testing, respectively. T-tests were used to compare the control and treated groups for each material.
Tensile strength results
The mean tensile strength of the control PC specimens was 58.500 MPa; the mean for UV-treated PC was 57.560 MPa. The reported mean difference was 0.939 MPa, with t=6.549 and p=0.000. The group means show a small decrease in PC tensile strength after treatment.
For PLA, the control group mean was 42.140 MPa and the treated group mean was 46.760 MPa. The reported mean difference was -4.620 MPa, with t=-3.955 and p=0.004. The measured PLA tensile strength was higher after the treatment. The sign of a reported mean difference depends on the order in which the groups are subtracted; the group means show the direction of the change.
The two polymers therefore did not follow the same tensile-strength trend in this experiment. PC had a lower mean after UV exposure, whereas PLA had a higher mean. The paper describes the UV influence on tensile strength as more pronounced for PLA than for PC.
Flexural strength results
Mean flexural strength increased for both materials. PC rose from 89.956 MPa in the control group to 92.986 MPa after treatment. The paper reports a mean difference of -3.032 MPa, t=-10.501 and p=0.000.
PLA rose from a control mean of 77.140 MPa to a treated mean of 87.239 MPa. The reported mean difference was -10.098 MPa, with t=-10.955 and p=0.000. The paper reports statistically significant differences for both materials and a greater UV influence on PLA flexural strength than on PC. Each mean represents five specimens in its group; it should not be read as a prediction that every printed part will have exactly that strength.
What the findings mean for product development
For engineers and designers, the main practical point is that one should not assume UV exposure changes different FDM polymers in the same way. Under the conditions tested, PLA had higher measured tensile and flexural strength after exposure. PC had lower measured tensile strength but higher measured flexural strength. Material selection should therefore take account of the expected loading and operating environment, rather than relying only on a filament’s nominal properties.
These results do not establish that PLA or PC components will become stronger during long-term outdoor use. The specimens received a 24-hour laboratory treatment, and the study tested one printer, one print orientation and one parameter set for each material. It does not establish product lifetime, outdoor durability or performance under other types of loading. For product development, education or industrial prototyping, the results are best understood as a controlled comparison—not as a universal material specification or a substitute for testing the intended component.
Limitations and next steps
There were five specimens in each material-and-treatment group. The experiment can compare those groups, but its sample size and setup do not represent every filament, printer or printing condition. The specimens were all printed in the flat XY orientation, and the study tested tensile and flexural strength rather than a wider set of mechanical properties.
The paper calls for further research to understand the mechanisms behind the different PC and PLA responses and to optimize material performance under UV exposure. The paper does not identify an optimal exposure condition. Further testing would be needed to evaluate other materials or conditions and to validate a specific printed product. A result for one filament and process should not automatically be transferred to another.
Conclusion
Published in TEM Journal in 2023, this study found that 24 hours of continuous UV treatment produced different tensile-strength trends in FDM-printed PC and PLA specimens. PC tensile strength decreased, while PLA tensile strength increased; flexural strength increased for both materials. The reported t-tests identified statistically significant differences between treated and control groups. The findings underline the importance of evaluating the particular polymer and exposure conditions when assessing 3D-printed parts, while further testing is needed before drawing conclusions about long-term use.
| Authors | Adi Pandžić, Damir Hodžić, Džana Kadrić, Edin Kadrić |
|---|---|
| Published in | TEM Journal, 2023, Volume 12, Issue 4, pp. 1921–1928 |
| Publication date | November 9, 2023 |
| DOI | 10.18421/TEM124-01 |
| Full paper | researchgate.net |
Frequently asked questions
How did UV exposure affect the tensile strength of PLA and PC?
After 24 hours of exposure, mean PLA tensile strength increased from 42.140 MPa to 46.760 MPa, while mean PC tensile strength decreased from 58.500 MPa to 57.560 MPa.
Did UV exposure change the flexural strength of PLA and PC?
Yes. Mean flexural strength increased from 89.956 MPa to 92.986 MPa for PC and from 77.140 MPa to 87.239 MPa for PLA.
How were the FDM specimens exposed to UV radiation?
They received continuous UV exposure for 24 hours under ISO 4892-3, Method B, in a chamber set to 50 °C.
This article summarises a published research paper; please refer to and cite the original paper. About the author
