What kind of rubber band is this that can achieve great results with just a little effort?

Produced by: Science Popularization China

Author: Shi Chang (PhD in Physical Chemistry)

Producer: China Science Expo

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With the rapid development of science and technology today, 3D printing technology is like a strong east wind, blowing through all walks of life. From complex and precise mechanical parts to lifelike models, from fantastic architectural prototypes to personalized daily necessities, 3D printing technology, with its infinite creativity and flexibility, illuminates people's imagination into reality, bringing convenience and surprise to our lives.

3D Printing Production Model

(Photo source: veer photo gallery)

Do you know about 3D printing technology?

3D printing technology, also known as additive manufacturing technology, is an innovative production method that builds three-dimensional entities by stacking materials layer by layer. The principle of 3D printing technology is similar to building a house with bricks, which can be simply summarized as "layered manufacturing, layer by layer".

The entire process of 3D printing is not complicated. First, a digital model is created or obtained through computer-aided design software, and then the model is cut into a series of very thin cross-sectional layers (i.e. slices), with each layer thickness usually ranging from tens to hundreds of microns. Then, the 3D printer builds the final object layer by layer based on the slice information through specific technology and materials.

3D printing processes include fused deposition modeling (FDM), photo-stereolithography 3D printing (SLA, DLP, LCD), selective laser sintering (SLS), selective laser melting (SLM), stereo inkjet printing (3DP), and layer-by-layer manufacturing (LOM).

3D printer in action

(Photo source: veer photo gallery)

Fused deposition modeling technology is to heat and melt filamentary thermoplastic materials through a nozzle, deposit them layer by layer on a platform, and finally solidify them into a three-dimensional object. The commonly used raw materials for this technology are thermoplastic materials, such as ABS (acrylonitrile-butadiene-styrene copolymer) and PLA (polylactic acid). This technology has low requirements for equipment and is easy to operate, suitable for individuals and small studios. The "radish knife" and "telescopic sword" that are popular in the toy market recently are made in this way.

The principle of photocuring 3D printing is to use light of a specific wavelength and shape to irradiate photosensitive resin, and then solidify the photosensitive resin layer by layer to generate an object of the desired shape. This technology has high molding accuracy and smooth surface, and is suitable for making fine models and small parts.

Selective laser sintering uses a laser beam to scan powder materials, melt them and bond them together, and accumulate them layer by layer into a three-dimensional object. This technology uses powder as raw material (such as nylon, metal powder, ceramic powder, etc.), has high molding accuracy, and is suitable for manufacturing complex structures and functional parts.

Selective laser melting is similar to selective laser sintering, but the laser energy is higher, which can completely melt the metal powder and achieve rapid prototyping of metal parts. This technology often uses metal powder (such as titanium alloy, stainless steel, etc.) as raw materials, and can print high-strength and high-precision metal parts. It is widely used in aerospace, medical and other fields.

3D inkjet printing uses powdered materials (metal or non-metal) and adhesives as raw materials, and uses the bonding mechanism to print each component layer by layer. The sample formed by this printing technology has the same color as the actual product, and it is currently a more mature color 3D printing technology.

Laminated solid manufacturing uses thin sheet materials (such as paper, plastic film, etc.) and hot melt adhesive as raw materials, and accumulates the required object layer by layer through laser cutting and thermal bonding. This technology has a fast molding speed and low material cost, and is suitable for making large structures and shells.

Although 3D printing technology is relatively mature and the product restoration is high, due to the limitation of printing raw materials, 3D printed products are highly brittle and easily broken by external forces. When such products are used in scenarios with high mechanical performance requirements, they seem to be somewhat "incapable". So, how can we improve the fragile heart of 3D printed products and make them both "good-looking" and flexible?

On July 3, 2024, Chinese scientists published a research result on 3D printed elastomers in the journal Nature. The rubber bands prepared using this technology can be stretched to 9 times their own length, and the maximum tensile strength can reach 94.6 MPa, which is equivalent to 1 square millimeter being able to withstand a gravity of nearly 10 kilograms, showing super high strength and toughness.

The research results were published in the journal Nature

(Image source: Nature magazine)

What makes this rubber band so special?

In the process of photocuring 3D printing, in order to improve production efficiency, a faster molding speed is often required, which leads to an increase in the cross-linking density of the material and a decrease in the toughness of the material during the curing process. Conventional methods of increasing the toughness of the material will increase the viscosity of the material, reduce fluidity, and lead to a decrease in molding speed. The contradictory relationship between the molding speed of 3D printing and the toughness of the finished product has always troubled the entire industry.

However, these two contradictions have been "reconciled" by Chinese scientists. Through the analysis of the raw material photosensitive resin of light-curing 3D printing and the disassembly of the printing process, the researchers proposed a strategy of printing and post-processing in stages. The researchers designed a DLP (digital light processing) precursor of dimethacrylate, which contains a dynamically hindered urea bond and two carboxyl groups on the main chain. During the printing and molding stage, these key components are in a "dormant" state, and play a toughening role in the post-molding processing stage.

a. 3D printed objects and their dimensional changes during post-processing; b. Anti-puncture performance of 3D printed balloons; c. Modeling of mechanical puncture force; e. 3D printed pneumatic gripper weight lifting test

(Image source: Reference 1)

During the post-processing stage at 90°C, the hindered urea bonds in the 3D printed products dissociate to generate isocyanate groups, which on the one hand form amide bonds with the side chain carboxyl groups, and on the other hand react with water adsorbed by carboxylic acids to form urea bonds. The changes in chemical bonds within the molecules connect the single network structure in the material into an interpenetrating network structure similar to "hand in hand", and bring more hydrogen bonds, which strengthens the internal structure of the material. It is precisely because of the changes in the internal structure of the material that the 3D printed products have a larger buffer space when deformed by external forces, similar to the energy absorption effect during a vehicle collision, which improves the product's impact resistance and fracture resistance, and has higher toughness.

The experimental results show that the film with a thickness of only 0.8 mm prepared by 3D printing using DLP precursors exhibits extremely strong anti-puncture performance and can withstand a force of 74.4 N without breaking. Even under high-pressure inflation conditions, the 3D-printed pneumatic gripper can still grab a copper ball weighing 70 grams with sharp thorns on the surface without breaking, demonstrating the ultra-high toughness and structural strength of 3D-printed products.

What are the applications of 3D printed elastomers?

In the field of sports equipment , 3D printed elastomers provide athletes with more personalized, high-performance equipment. For example, customized insoles and protective equipment use the shock absorption and support characteristics of elastomers to optimize athletes' sports performance and enhance the wearing experience. Especially in extreme sports and high-impact sports, 3D printed elastomer materials can significantly reduce the impact on athletes during exercise and protect their joints and muscles from damage.

3D printed insoles

(Photo source: veer photo gallery)

In the automotive and aerospace fields , 3D printed elastomers are used in key components such as lightweight shock absorbers and seals. These components have complex structural designs that reduce weight while maintaining high performance.

Auto Parts

(Photo source: veer photo gallery)

In the field of electronic products , smart speakers, smart bracelets, mobile phone cases and other products can be printed with elastomeric materials. These products not only have excellent softness and elasticity, but also have high wear resistance and durability, which can meet consumers' multi-faceted demands for product appearance and performance.

Smart Bracelet

(Photo source: veer photo gallery)

In the field of industrial manufacturing , 3D printing elastomer technology is used to manufacture various industrial molds and transmission belts. These parts need to withstand greater mechanical stress and vibration, and elastomer materials are ideal choices due to their excellent elasticity and fatigue resistance. Manufacturing these parts through 3D printing technology not only improves production efficiency but also reduces manufacturing costs.

Conveyor Belt

(Photo source: veer photo gallery)

Conclusion

3D printing technology plays an increasingly important role in our lives, and the advent of 3D printing elastomer technology has further enriched the use scenarios of 3D printing products. The advancement of science and technology has given life infinite possibilities, and we also look forward to more technological development and technological innovation to make our lives more colorful.

References:

1.Fang, Z., Mu, H., Sun, Z. et al. 3D printable elastomers with exceptional strength and toughness[J]. Nature, 2024.

2.Walker, DA, Hedrick, JL & Mirkin, CA Rapid, large-volume, thermally controlled 3D printing using a mobile liquid interface[J]. Science, 2019.

3. Zhang Xuejun, Tang Siyi, Zhao Hengyue, et al. Research status and key technologies of 3D printing technology[J]. Materials Engineering, 2016.

4. Huang Jian, Jiang Shan. Will 3D printing technology set off the "third industrial revolution"? [J]. New Materials Industry, 2013.