Hollow Glass Microspheres,A Weapon for Lightweighting~

 

Kelly Chemical provides various specifications of hollow glass microsphere materials, effectively enhancing the added value of products.

 

The development of the times has placed higher demands on materials, such as lighter shoes, more fuel-efficient cars, more environmentally friendly plastic products, better processing performance, and higher product quality, among others. These are the driving forces behind material innovation. As a new type of functional filler, hollow glass microspheres are gradually coming into the spotlight in the materials field, bringing infinite possibilities for innovation.

 

Application of Hollow Glass Microspheres in Resin Systems:

 

High-strength, low-density hollow glass microspheres can be used as lightweight additives in various polymers and applications, while maintaining or improving processing performance and physical properties of materials. Hollow glass microspheres can be used in various resin systems, including:

 

1)Polyolefins, nylon composites, and other thermoplastics

2)Thermosetting materials, liquids, and pastes

3)Sheet molding and bulk molding composites

4)Elastomers

5)Wood/plastic composites

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Performance Enhancement of Resin Systems by Hollow Glass Microspheres:

 

Hollow glass microspheres can withstand the temperature and pressure conditions of blending, injection molding, extrusion, and other manufacturing processes. Proper use can improve product quality:

 

1)Improve flowability

 

Hollow glass microspheres are tiny spheres that act as miniature ball bearings in resin, providing better flowability than flake, needle-shaped, or irregularly shaped fillers. The resulting microsphere effect reduces the viscosity of the mixture, resulting in excellent mold filling properties and significantly improved processing performance, increasing production efficiency by 15% to 20%.

 

2)Reduce shrinkage and warpage of products

 

Because spherical objects are isotropic, filling with hollow glass microspheres can overcome the inconsistency in shrinkage caused by orientation, ensuring the dimensional stability of the product and reducing warpage. It solves the deformation problems that have always existed in the molding and processing of profiled materials and large injection-molded products. Additionally, using hollow glass microspheres as fillers increases the processing speed of filled modified materials and improves production efficiency.

 

3)Lower oil absorption

 

The oil absorption rate of hollow glass microspheres is 0.20 to 0.60 cc/g. Due to its spherical structure, the specific surface area per unit volume is lower, resulting in a lower oil absorption value.

 

4)More economical in terms of volume cost

 

The density of high-performance hollow glass microspheres is only 1/5 to 1/2 of that of the resin, so only a small amount of hollow glass microspheres is needed to replace heavier powdery materials with the same volume. When considering the unit volume cost, filling applications can reduce product weight, thereby reducing the amount of main raw materials such as resin and rubber and reducing product costs.

 

Processing and Usage Recommendations for Hollow Glass Microspheres in Thermoplastic Materials:

 

To fully exploit the advantages of hollow glass microspheres, it is necessary to ensure that the hollow structure remains intact during addition. The high shear in the twin-screw extruder is easy to break the hollow glass microspheres. Once broken, the hollow glass microspheres become glass fragments with a density of 2.5 g/cm³, which cannot achieve the weight reduction effect. This is the main reason why many application products did not achieve the desired effect in the initial stage of experimentation. Therefore, reducing the breakage rate of hollow glass microspheres during the granulation process of the twin-screw extruder is the key to exerting the excellent performance of hollow glass microspheres. Specific considerations can be made from aspects such as the screw combination of the extruder, feeding and cutting methods, main machine speed, and pressure resistance of hollow glass microspheres.

 

1.Adjustment of the twin-screw extruder screw combination

 

In the twin-screw extruder, the screw exerts shear force on the material to evenly disperse the filler. The spherical shape of hollow glass microspheres is easier to disperse, and excessive shear force is prone to breakage. Therefore, adjust the angle of engagement of the screw segment to reduce the shear force. The specific adjustment method is as follows:

 

 

 

Comparison of the fracture rate before and after screw combination adjustment-

 

Hollow Glass Microspheres	Before screw combination adjustment	After screw combination adjustment
HS46	14-15%	3-4%
HL60S	11-12%	2-3%

(Data source: original factory R&D laboratory)

 

2.Adjustment of feeding method

 

To effectively reduce the breakage rate of hollow glass microspheres, the following should be considered in the process:

 

1)Choose side feeding to reduce the probability of hollow glass microspheres being sheared in the screw.

 

2)Choose long particle granulation to reduce the mechanical damage during granulation.

 

After improvement of screw combination

 

Comparison of fracture rates caused by different feeding methods and granulation methods:

 

	HS46	HL60S
Fracture rate of main feeding port short particles	18-20%	16-18%
Fracture rate of main feeding port long particles	13-15%	11-13%
Fracture rate of side feeding port short particles	8-10%	6-8%
Fracture rate of side feeding port long particles	3-4%	2-3%

(Data source: original factory R&D laboratory)

 

Note:

 

1.The hollow glass microsphere models selected for the experiment are HS46 and HL60S.

2.HS46, compressive strength: 16000 psi, D90 (typical value) 30 μm, specific gravity 0.46 g/cm³.

3.HL60S, compressive strength: 18000 psi, D90 (typical value) 55 μm, specific gravity 0.60 g/cm³.

 

3.Impact of twin-screw machine speed

 

When the speed is high, the material is subjected to greater shear force, making hollow glass microspheres more prone to breakage. Therefore, under the premise of ensuring the production process, reduce the speed to minimize the shear force of the screw.

 

After improvement of screw combination, under conditions of long particle granulation and side feeding

 

Comparison of fracture rates caused by different screw speeds:

 

Speed(r/min)	100	200	300	400
Microsphere content (wt%)	10	10	10	10
Microsphere fracture rate(%)	2.0-2.5	3.0-3.5	4.0-5.0	6.0-7.5

(Data source: original factory R&D laboratory)

 

When the content of hollow glass microspheres is around 10wt%, the fracture rate of hollow glass microspheres increases with the increase of screw speed, reaching 7.23% at 400r/min.

 

4.Common problems and solutions

 

1)What is the normal breakage rate of hollow glass microspheres during extrusion?

 

Due to the processing method, hollow glass microspheres will have a certain breakage rate during extrusion.

 

Optimization solution:

 

Adjust the screw combination, side feed hollow glass microspheres, long particle granulation, and control the breakage rate at 2-3%.

 

2)Does the addition of hollow glass microspheres affect the processing performance of the resin?

 

Hollow glass microspheres are inorganic powder fillers,similar to other inorganic fillers, the addition can enhance the heat resistance of the resin, thereby increasing the processing temperature.

 

Solution:

 

1.Maintain the original processing temperature of the extruder.

2.Add a small amount of lubricant to the formulation to address the issue.

 

3)After the addition of hollow glass microspheres as side feed, how to ensure the uniformity of the feed?

 

Solution:

 

1.Select double-screw forced feeding for side feeding.

2.Use agitator sticks in the side feeding to prevent "bridging" of hollow glass microspheres and ensure uniform feeding.

 

4)Will the mechanical properties of the resin significantly decrease after adding hollow glass microspheres?

 

Adding hollow glass microspheres will sacrifice some impact resistance but can enhance certain flexural moduli.

 

Improvement methods:

 

1.Add a small amount of toughening agent.

2.Modify the surface of hollow glass microspheres with coupling agents to improve their bonding performance with the resin.

 

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