Injection : HDPE vs PP

Hello ! I'm just starting my Precious Plastic journey. I'd like to craft kitchen knives handles with an injection machine. What would be the best option between using HDPE and PP ? Let's cut down on waste ! Thanks for your help, Joe

2

1

You can pretty much use all types of plastic for kitchen knifes, due they are not limiting you in the pressure you need by the machine (more thick than e.g. an electronics case). I have seen them made from HDPE - but other types work too.

1

@Second Slice funny you mention kitchen knives, we're actually working with @Thomas Peterberns | Johannplasto to develop an open source version

1

3

12:35 PM

If you’re not in a rush we'll release all the drawings sometime in Q1 2024

Mattia

@Second Slice funny you mention kitchen knives, we're actually working with @Thomas Peterberns | Johannplasto to develop an open source version

I'd like to start with a bigger knife version but I'll keep a close eye on it as refurbishing table cutlery from my local market is definitely part of the plans !

@Second Slice I would recommend you utilise PP, the main reason being that it can handle deformation caused by the pressure of bolts, pins, or knife inserts much better than HDPE. HDPE doesnt spring back as easily, this is why PP is used for garden furniture instead of HDPE. Plus PP shrinks less so if you want a thick handle, you can potentially get away with a slightly thicker one without sink marks vs HDPE. Though sink marks also related to mould design, plastic additives, colour and machine.

2

HDPE (High-Density Polyethylene) Strength and Durability: HDPE is known for its strength and rigidity. It's less likely to get scratched and can withstand higher temperatures compared to PP. Ease of Processing: It melts at a slightly higher temperature (around 130°C to 137°C) than PP. This might require a bit more energy in the injection process. Chemical Resistance: Excellent resistance to a wide range of chemicals, which is beneficial for kitchen environments. Recyclability: Widely recycled and generally easier to source in various colors and forms. PP (Polypropylene) Flexibility: PP is more flexible than HDPE, which can be an advantage or disadvantage depending on the design and use of the knife handles. Melting Point: It has a lower melting point (around 130°C) than HDPE, which might make the injection process slightly easier and more energy-efficient. Chemical Resistance: Good resistance to chemicals, but slightly less than HDPE. Impact Resistance: It has better impact resistance, especially at lower temperatures. Considerations for Kitchen Knife Handles Heat Resistance: Since kitchen knife handles may be exposed to varying temperatures, HDPE's higher temperature tolerance could be advantageous. Durability and Feel: HDPE's rigidity might offer a more solid feel, important for a kitchen knife handle. However, if a slightly softer, more flexible handle is preferred, PP could be a better choice. Aesthetics and Finish: Both plastics can be sourced in various colors. HDPE might have a slight edge in achieving a glossy finish.

2

Recycling Machinery

HDPE (High-Density Polyethylene) Strength and Durability: HDPE is known for its strength and rigidity. It's less likely to get scratched and can withstand higher temperatures compared to PP. Ease of Processing: It melts at a slightly higher temperature (around 130°C to 137°C) than PP. This might require a bit more energy in the injection process. Chemical Resistance: Excellent resistance to a wide range of chemicals, which is beneficial for kitchen environments. Recyclability: Widely recycled and generally easier to source in various colors and forms. PP (Polypropylene) Flexibility: PP is more flexible than HDPE, which can be an advantage or disadvantage depending on the design and use of the knife handles. Melting Point: It has a lower melting point (around 130°C) than HDPE, which might make the injection process slightly easier and more energy-efficient. Chemical Resistance: Good resistance to chemicals, but slightly less than HDPE. Impact Resistance: It has better impact resistance, especially at lower temperatures. Considerations for Kitchen Knife Handles Heat Resistance: Since kitchen knife handles may be exposed to varying temperatures, HDPE's higher temperature tolerance could be advantageous. Durability and Feel: HDPE's rigidity might offer a more solid feel, important for a kitchen knife handle. However, if a slightly softer, more flexible handle is preferred, PP could be a better choice. Aesthetics and Finish: Both plastics can be sourced in various colors. HDPE might have a slight edge in achieving a glossy finish.

Looks like you switched HDPE and PP.