This summer I spent some weeks in our apartment flat in Sesimbra, Portugal which by the way you can rent for your holiday as well. I used this time to check on my experiment which I started in January 2021.
Flashback: experiment setup
I cut a 240x160x0.1 mm part out of a standard HDPE bag and put it in a marmalade glass which is filled with seawater from the California beach of Sesimbra. I stored it in a room without the influence of sunlight.
20 month later
In August 2022 I opened the marmalade glass again and removed the HDPE piece. I checked it for damages such as cracks and holes. However, no visible damages could be found so far. Figure 1 shows the HDPE piece. After the check was finished I put it back and placed the glass in the dark room. If the glass would be impacted by sunlight, degradation may occur faster.
Figure 1: Removed HDPE piece of plastic bag from sea water filled glass
I will give you an update in 2023 again.
Generally, keeping in mind the four major factors (material, component design, part processing, service conditions) impacting plastic part performance during your polymer material selection and part design phase will decrease part failure in the long run.
Thanks for reading and #FindOutAboutPlastics!
Greetings,
Herwig Juster
Interested to talk with me about your polymer material selection, sustainability, and part design needs - here you can contact me
Hello and welcome to a new blog post. Today I will show you another set of multipoint design data: specific heat capacity as a function of temperature.
In a previous post I presented to you the Global Warming Potential (GWP) as a function of the heat capacity. However, the heat capacity values were limited to one temperature only (20°C).
Increasing the temperature of a polymer by a dT at constant pressure is the result of a specific amount of heat supplied to the system. This is referred to as specific heat.
Figure 1 presents the specific heat of amorphous and semi crystalline unfilled polymers. With increasing temperature the specific heat of both amorphous and semi crystalline polymers is increasing.
Figure 1: Specific heat capacity Cp as a function of temperature of amorphous and semi crystalline unfilled polymers.
There are several calculations in polymer engineering where the specific heat value of a certain polymer is needed:
-calculation of the pressure drop along the gate or runner of an injection mould
Hello and welcome back to a new post. Today we continue with polymer property data as a function of time. Multipoint data play a key role during material selection and part design. Properties over a temperature range are especially interesting for us part designers.
In a previous post we discussed the Coefficient of Linear Thermal Expansion (CLTE) of unfilled and filled polymers at room temperature (20°C). Here you can find the post and the data.
CLTE of unfilled polymers as a function of temperature
The Figure 1 below shows the CLTE values of amorphous and semi crystalline unfilled polymers. With increasing temperatures we see higher thermal expansion due to the easier movement of the polymer chains. It is important to check the CLTE of your selected material at operating temperature too. This will avoid unexpected part failures. Also, if metal overmoulding is done, such a check is in particular important.
Figure 1: CLTE of unfilled polymers as a function of temperature
Here you can find further design property data of various polymers for your part design and material selection.
Thanks for your reading and #findoutaboutplastics
Greetings,
Herwig Juster
Interested to talk with me about your polymer material selection, sustainability, and part design needs - here you can contact me
Hello and welcome to a new blog post. Today we discuss the thermal conductivity of amorphous and semi-crystalline polymers (unfilled; only the polymer resin) as a function of temperature.
The importance of multi-point data
Multipoint data of different polymer and polymer compound properties prevail information which would otherwise may be overlooked during material selection and product design.
In other posts we discussed multi-point data such as the DMA results of engineering and high performance polymers. Multi-point data are important for material selection since it has a lot to do with thinking in relationships of time-dependency and temperature-dependency behaviors. Graphically such behaviors can be better accessed. Single point data can lead to misjudgment and negatively impact the material selection process.
Thermal conductivity of polymers was already several times topic on this blog:
However, in those posts thermal conductivity mostly was discussed as a value estimated at one single temperature. Now we look how the thermal conductivity changes in a temperature range of -150°C and up to 150°C. There is no linear behavior of the different polymers in this temperature range.
Amorphous polymers: thermal conductivity as function of temperature
Amorphous polymers: thermal conductivity as function of temperature
Semi-crystalline polymers: thermal conductivity as function of temperature
Semi-crystalline polymers: thermal conductivity as function of temperature
Here you can find further design property data of various polymers for your part design and material selection.
Thanks for reading and #findoutaboutplastics
Herwig
Interested to talk with me about your polymer material selection, sustainability, and part design needs - here you can contact me
Hello and welcome to a new post. Today we discuss the starting point in polymer material selection.
In general there are several procedures for material selection such as the Ashby methodology or my own developed funnel approach.
However, all the selection processes and procedures should have the definition of the part requirements as their common starting point.
How to do it the best?
Figure 1: Polymer Material Selection - Estimation of product requirements as common starting point
Covering effectively the product requirements, a combination of functionality questions and selection factor questions can support you to achieve this (Figure 1).
First we have to ask some questions on the functionality of the part. Following questions can help us with this assessment:
-What are the performance requirements (structural, etc.)?
-Do you want to combine multiple parts or functions?
-What will be the structural load of the part (static, dynamic, cycling, impact, etc.)?
-What will be the environmental impact on the part (chemical, temperature, time)?
-What is the expected lifetime of the product?
With the collected answers we can define the part requirements as accurately as possible. Together with the understanding of the differences of thermoplastics (amorphous and semi-crystalline) and thermosets we have an understanding of the performance, thermal and mechanical properties, as well as chemical resistance and processing differences of thermoplastics and thermosets.
Selection factors - checklist for your material selection
There are more detailed lists , however in this post we cover the six essential questions on material selection factors.
1. What is the service environment of your part?
-what is the operating temperature: high, low, duration, thermal expansion
-exposure to chemicals, solvents, lubricants, salt
-exposure to water and humidity
-UV stability for use in outdoor / indoor environment
2. What are the regulatory requirements?
-flammability rating needed such as UL 94 at different wall thickness
-food contact
-fulfillment of medical standards
-any other regulation such as IP 44 for electrical devices
3. What types of load at which service temperature need to be fulfilled?
-continuous load represented by Young modulus and creep resistance
-intermittent load represented by tensile strength
-impact load represented by impact strength
-fatigue represented by cycles to failure for example over a Wöhler curve
4. Other considerations such as:
-dimensions and tolerances which need to be met
-electrical properties such as CTI, electrical breakdown strength
-wear and friction
-thermally conductive materials with or without electrical isolation
-aesthetics and colour (relevant for application with food contact, and toys)
-painting and printing
-life time needs
5. What is the processing and fabrication method?
-injection moulding, extrusion, thermoforming
-assembling by using screws, laser welding, or adhesives
-secondary operations
6. What are the economic and commercial considerations
-useful to make when material short-list is available
Conclusions
The combination of questions on part functionality and selection factors will help to facilitate your polymer material selection, together with fundamental data in a systematic way.
Thank you for reading and #findoutaboutplastics
Greetings,
Herwig
Interested to talk with me about your polymer material selection, sustainability, and part design needs - here you can contact me
