5 instructions on molded pulp 3D printing

Table of Contents

To successfully engage in molded pulp 3D printing, begin by preparing a smooth pulp from shredded and soaked paper. Enhance the mixture by incorporating a 5% starch binder for structural strength. Use a 1.5 mm nozzle on your 3D printer, set to a slow print speed of 20 mm/s and a precise layer height of 0.5 mm. After printing, dry the objects at 60°C and finish by sanding with fine-grit sandpaper to achieve a smooth surface.

Prepare the Pulp Mixture

Assembling a pulp mixture is the starting point in molded pulp 3D printing. The step is paramount in realizing optimum print quality and sturdiness in the final product. First and foremost, secure recycled paper – preferably post-consumer waste, as it ca be considered as a responsible choice from a process sustainability perspective. Shred the paper into pieces no larger than one square inch to achieve uniformity in the pulp mixture. Include about two liters of warm water in every kilogram of locally available recycled paper to hasten the breakdown process.

Subsequently, blend the soaked paper using a commercial grade blender, which would in turn result in fine, consistent pulp. Failure to achieve an appropriate level of smoothness – even within such a rudimentary designed product as a motor – would yield a surfaced print. On the other hand, if using the occasional agricultural waste like rice husks or wheat straw, grind these grasses to dust to disturbance favoritism – or fire directly into the production matrix. This might require additional equipment – a better blender or an actual grinding process. Mix the product in uniform fashion for an additional level of quality.

Mix in a natural binder for sturdiness. Starch is a common choice for such things, and can be added a 5% of the dry weight of the mold. This promotes adhesion amongst the layers and durability of the final product. Add a natural colorant, such as 10 grams of cocoa powder to a kg of pulp for dyed material with a fragrance I personally enjoy. The pulp should form a consistency resembling a dense smootie, in order to allow the easy passage through a 3D printer’s. The machine’s print head is designed with a hole of about 1 – 2 millimeters in diameter, and it can be thus become clogged by a pulp mixture of inappropriate liquidity. Inversely, it is the user who is using water to clog up the machine in the first place!

Additives and Consistency Adjustment

One of the most important components of success in molded pulp 3D printing is the correct choice of additives and proper consistency. Not only it affects the printable properties of the pulp, but also the final product’s quality and usability. First of all, additives that can be applied are binders to make the pulp more resistant. One of the most popular choices is cellulose gum, which can be added at a 3% concentration of the pulp’s dry weight. Due to that, the final product’s tensile strength will increase significantly. To make the manufacturing process more sustainable, it is viable to use alginate, which is a natural polymer and can be derived from seaweed.

At a concentration of 2%, it has a better binding capacity than cellulose gum and at the same time is fully biodegradable. Another important additive to consider is colorant, as the final product will need an attractive color in applications where it is used on the visible part of some items. For this purpose, natural pigments may be employed, such as beetroot for red color and spirulina for blue. At a concentration of about 0.5%, they will make the color look clearly, but they will not adversely affect the physical properties of the pulp, maintaining its tensile strength on a required level. Moreover, water dispersion of the pulp should also be adjusted.

It is highly important for 3D printing for the pulp to be diluted enough to pass through the nozzle, but at the same time viscous enough to keep the desired shape after that. As a general rule, about 10,000 cps should be an acceptable viscosity for the pulp that will be used with a 1.5 mm nozzle printer, which is close to the viscosity of thick cream. The consistency of such mixtures will affect the speed of extrusion and drying times. Therefore, slightly thinner mixtures will print faster, but it will take more time to dry — thus, the total manufacturing time will be increased and the still-wet form might deform under the influence of its own weight. On the other hand, a thicker mixture will print very slowly, but it will still permit faster drying and provide better dimensional stability.


3D Printer Setup

A proper setting of a 3D printer for molded pulp printing is possible only after a range of critical adjustments that can ensure the necessary conditions for appropriate printing. First and foremost, it is important to select a printer that is capable of working with viscous materials. Typically, it requires a printer with a strong extrusion system because it is evident that it is not a trivial task to make something continuously go through a small hole for a long time. Therefore, in this case, a printer with a screw extruder is preferable to apply the necessary pressure in a more or less steady way. Furthermore, the screw is often preceded by another apparatus called the gear pump, whose role is to generate proper pressure. The nozzle, in this case, can be rather wide to make sure that no clogs could damage the print; the medium diameter usually reaches 2 mm. Thus, the detail is ensured, and the danger of damage is removed.

The print bed is also a critical aspect. In this case, it should first and foremost provide proper’ adherence and not allow the wet pulp to deform or move the first layer and subsequent ones. As a rule, a specific coat is applied to the print bed – experience shows that it should be a natural adhesive, such as a solution of guar gum. This coat ensures that the first layer sticks to the print bed, but it does not harm the biodegradability of the final product. Furthermore, the mild heat is usually applied to the print bed – it is about 30 to 40 degree Celsius, as it is always preferable to have the first layer dried as quickly as possible, so that it would not be deformed by the next layer. At the same time, it should be far from drying too quickly, as the layers should inevitably intersect to provide the sturdiness of the final product, for this reason, round objects are preferred.

Fastness of the flow is an excellent property, which, however, requires particular settings. The appropriate print speed should be reduced so that the given layer would have enough time to stabilize in every case. Experience shows that a parameter of about 20 mm per second is optimal, as it also ensures enough time and provides a decent throughput. The proper layer height is about 0.5 mm, as it ensures a good intersection of layers resulting in a sturdier final product. Finally, the regular calibration of the printer is another critical aspect as partially dried out pulp can actually clog the extruder and the nozzle.

Design and Printing Parameters

Selecting the appropriate design and printing parameters is crucial for optimizing molded pulp 3D printing. In this procedure, the interplay between the settings on the design software, the material property of the pulp, and the characteristics of the 3D printing technology must be thoroughly understood. The design should first be drawn in a 3D modeling software and exported in a format that can be read by the 3D printer selected, such as STL or OBJ. However, experience has revealed that understanding of the natural shrinkage and deformation of the pulp can also significantly affect the final result. Making simply the walls of your object 10% thicker will pay attention to the effect that the drying of the pulp will have on the final dimensions of your object.

A print with layer height greater than 0.5 mm would tend to have a rough aspect both because of the roughness of such large layers and also due to insufficient superposition to bond the different layers of pulp as they dry. These would also have to be increased. The layer superposition in each print directly influences its resistance. However, being very sensitive to deformation, any minimal superposition greater than 0.2 mm will be enough to allow the entire layer added to adhere and bond to the layer below. On the other hand, print speed is another design parameter that should be carefully pondered. A print speed greater than 20 mm/s is considered adequate since it allows each layer to stabilize before the next one is applied. Such a high speed would make the fusing of each pulp layer impossible.

Material use is also an important factor; however, print time can be reduced significantly and there is no need to make extra infill in the innermost parts of the object above 50%. Any lower infill percentage would be inability to support the outer pulp layers and any larger amount would mean unnecessarily consumed printing time and material. Finally, the object’s orientation during printing is also an fastidious factor. It is always best to choose the orientation that requires the least support. This is specifically applicable to 3D printing with pulp since it is very detrimental to the final object to have pulp parts that are not removed after printing. For example, printing a cup upside down is the most optimal because allows most of the object to be printed without support and is far more simpler to properly use a delaminator since the overhangs can easily be printed without support.

Drying and Finishing

The third step in molded pulp 3D printing, drying and finishing, is critical to achieving the desired strength, stability, and appearance of the final product. Drying not only solidifies the shape but also positively influences the material properties, while finishing methods improve the surface touch, how it looks, and the overall performance of the object.

After the completion of the printing process, making sure that the object dries uniformly, and no warping or uneven shrinkage takes place is the first step. The drying room should have room temperature to speed up the process, but it still may take from twenty-four to forty-eight hours due to the conditions and the thickness and complexity of the object. However, using a drying oven set to a low temperature of about fifty to sixty degrees will facilitate a controlled drying process and shorten the drying time. It usually takes from six to twelve hours, and such an environment will speed up the evaporation of water without initiating the thermal degradation of the pulp.

After ensuring that the object is well-dried, checking its surface quality is crucial. In general, molded pulp artifacts have a rough surface, but sanding it with a fine-grit sandpaper will be enough to achieve noticeable results. A two-hundred to three-hundred grit sandpaper will smooth out the most offending parts of the rough surfaces, make them appealing to visual and tactile senses. This step is mandatory for all pubic applications, especially the consumer ones, due to the critical importance of the tactile and visual properties of the items. Moreover, to increase the overall durability and appearance of the object, treating it with a natural sealing agent such as beeswax or a biodegradable varnish would be suitable. It will enhance the water resistance of the object and make the surface of the pulp professionally polished. Only a small amount of the substance is needed, and the application should be administered by smearing it with a soft brush.

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