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Understanding the Degradation Mechanism of PLA: Why PLA Filament Can Get Brittle

Understanding the Degradation Mechanism of PLA: Why PLA Filament Can Get Brittle
Understanding the Degradation Mechanism of PLA: Why PLA Filament Can Get Brittle
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Welcome to a complete tutorial on degradation mechanism of PLA and answering the question that why PLA filament becomes brittle. In this blog, the first aspect that will be covered is a brief history of polylactic acid (PLA) and the factors that worked towards its degradation then we will proceed to the details of the degradation mechanism. There are many unknown aspects surrounding this material. We will bring the answers to the questions such as why PLA is weak in structure why it has so many breakdown products and how importantly the degradation process alters the various grades of PLA filament. Prepare to step into the world of PLA degradation, its applications and much more in what will be an exciting and informative experience that unveils the science behind PLA. With that said let’s start!

Contents show

What is PLA and How Does it Degrade?

PLA
PLA

Overview on Polylactic Acid and its known uses

PLA (Polylactic Acid) is a biodegradable thermoplastic that is obtained from renewable resources such as cornstarch or sugarcane. Owing to the fast growing economies, its potential market runs from 3D and 4D printing, packaging and medical implants amongst many others. The primary manner in which PLA is degraded is hydrolysis, a biochemical process that consists of breaking down a compound by adding water. Hydrolysis, in this case, can happen more quickly when certain factors increase, for example temperature, humidity and UV light which, ultimately make the material become more brittle porous over time.

The Basic Degradation Mechanism of PLA

Hydrolysis is the process through which PLA is broken down, where ester bonds are cleaved with water molecules cutting down long polymer chains into shorter chunks. Degradation can happen because of long exposure to heat, humidity, and UV light which can weaken the material structure over time thus making it brittle.

Factors Influencing the Degradation Rate of PLA

In my opinion, besides the basic chemical structure of the material, there are quite a number of factors which influence the degradation of PLA with the most important being the temperature. To begin with, if temperature is increased, the rate of hydrolysis also increases which results in the cleaving of polymer chains. I’ve also noted that moist areas tend to increase the rate of degradation because water molecules are critical in the process of hydrolysis. Areas with high moisture content or even water contact tend to hasten the process of degradation Furthermore, degradation of PLA is fueled by exposure to UV light which alters the bond structure of the material and this is more so when PLA is applied outdoors or places with high illumination. All these factors are interrelated in illustrating how some environmental or material use conditions may dramatically affect the life span of PLA.

Why Does PLA Get Brittle Over Time?

PLA Get Brittle Over Time
PLA Get Brittle Over Time

The Contribution of Hydrolytic Degradation in the Brittle Composites of PLA

As time passes, water molecules cause the polymeric chains of PLA to shorten, leading to loss of flexibility and mechanical strength which contributes to fragility. Moreover, exposure to heat, moisture, and UV worsens structural disintegration, further making it less durable and more brittle.

The Hydrolysis Rate Dependence on Environmental Factors during the PLA Decomposition and their Consequences

Environmental factors are critical when considering the complexity of PLA degradation. Increased temperature promotes hydrolysis enhancing the breakdown of polymer chains. Moisture also catalyzes this reaction while when the mature plant is exposed to UV for too long, it damages the structure at the molecular level. These collectively lead to the deterioration of mechanical and pliability properties of PLA making it brittle fast.

The Role of Polymer Chain Structure on Brittle Property

In my opinion, the brittleness of PLA materials is dependent on its polymer chain structures. The degradation process of the material causes the polymer chains to shorten, which results in less flexibility making the material more brittle. This is a common effect which I have seen on different occasions, for example when moisture, heat or other factors cause the internal breakdown process to start off much more rapidly. When selecting or applying PLA, I tend to always take into consideration the mechanical properties of the material as well as the conditions reducing the risk of brittleness and increasing the lifespan of the material.

Exploring the Degradation Products of PLA

Exploring the Degradation Products of PLA
Exploring the Degradation Products of PLA

The Main By-products and Their Consequences

The most frequently observed by-products of the degradation of the polylactide are oligomers and lactide. They occur as a result of the polymer chain being hydrolyzed into its monomers. The best part about lactic acid is its environmentally friendly because it is not toxic and can be easily absorbed into the natural systems. The only issue with lactide oil is that it can hypothetically get concentrated in closed systems which can then cut off the access of surrounding systems potentially destroying the application and ecosystem in the process.

How Lactic Acid Associates with PLA Degradation

Broadly speaking, lactic acid impacts PLA degradation as it is primarily the by-product generated by hydrolysis. When hydrolysis occurs, lactide is a residual that remains. It is only a matter of time before the greater amount of lactic acid triggers a response in the local area that lowers the pH level resulting in degradation of hydrolysis in equilibrium.

Dismantling of PLA Matrix: An Explanation.

In my experience, hydrolysis is the first step dissolution of PLA matrix. It includes water molecules penetrating into polymers and breaking ester linkages in polymers chains. I noticed that when this takes place, the material commences the onset of losing its structural integrity, and becomes weaker and more brittle with time. Other things that are important in this processes includes moisture and temperature. For example, more humid pressure will fasten the water entry, whereas higher temperature is useful in bond cleavage. Such situations exist quite often in wrorking with PLA, where the viscoelastic material is not easy to break down, and thus requires cold, dry storage. However, if the intention of use of PLA is in environments with prevailing breakdown, then knowing this mechanism helps me in improving the performance for that particular changing mechanism.

How Does the Degradation Process Affect PLA Filament?

How Does the Degradation Process Affect PLA Filament?
How Does the Degradation Process Affect PLA Filament?

How the changes in mechanical properties of PLA are affected by degradation

PLA filament is so degraded which now limits what it can be used for. This is the same for most Å¡ypercarnivore polymers. As time passes by, hydrolysis continues to occur which shortens the polymer chains making the material more brittle and shortening its tensile strength. As a result, the filament loses its flexibility as well as load bearing ability making it less useful in mechanical applications unless of course, enter degradation for a specific use case.

Analysing the degradation behavior of neat PLA and PLA based composites

Several trends are, in my opinion, worth noting as neat PLA is compared to PLA based Composites, specifically its behavior in regards to degradation. Neat PLA is a unidirectional constitutive with consistent mechanical properties when placed under the same environmental conditions so its degradation is expected to be uniform and at a consistent rate. Meanwhile PLA based composites are far more diverse thanks to the varying inclusions or reinforcements added, leading to varied degradation behavior for example composites with organic fillers, wood fibers might be prone to absorbing moisture occurring more frequently might trigger an area to undergo hydrolysis. Alternatively, moisture penetration may be slightly restricted in composites reinforced with inorganic filler glass or carbon fibres which limit degradation a little. From my experience, this level of detail is quite important especially when dealing with materials that are likely to be exposed to different environmental aspects/ultimately changing their properties making them more suitable for specific scenarios.

Is PLA Truly Biodegradable?

Is PLA Truly Biodegradable?
Is PLA Truly Biodegradable?

Investigating the Natural Degradation of PLA in Various Conditions

The conditions in which PLA is placed determines its biodegradability. For instance, if the temperature, moisture and microbial activity is adequate in the industrial compost, PLA can biodegrade to carbon dioxide, water and biomass in a period of 3 months or less. Contrarily, if the PLA is exposed to natural conditions and settings like the ocean, degradation is the total opposite as the conditions are fossils which results in an extended delay in the process as there are no microorganisms that would be able to consume the PLA. Therefore one could say that PLA is biodegradable but there is a catch, it does not dissolve in an efficient time across many environments without the right conditions.

The Problems Associated with Completely Decomposing of PLA

One of the major problems inhibiting individuals from completely decomposing PLA is the lack of facilities to generate optimal conditions. The conditions like high temperatures, moist soil and other various conditions are found in composting facilities, which if idealised in other environments PLA would completely disintegrate as well. Lack of temperature, moisture and sufficient microbial colonies results in PLA being inefficiently decomposed which is only possible through proper waste disposal and composting techniques.

Future Opportunities for PLA in Sustainable Use

In my opinion, PLA may be classed as biodegradable, although it is necessary to qualify it; it decomposes easily only under certain conditions, like in industrial composts. In natural ecosystems, whether they are soils or oceans, the requisite temperature for obliteration and microorganisms are absent, and hence PLA takes much longer to biodegrade in these ecosystems. To eliminate it totally, pellagic pollution management systems must be present, hence its biodegradability is very dependent upon how we manage and treat PLA waste.

Reference sources

Polylactic acid

Biodegradation

Polymer

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Frequently Asked Questions (FAQs)  

Q: What is PLA and why is it classified as biocompostable?

A: PLA, also known as polylactic acid, is a form of plastic which is manufactured from renewable resources like corn starch or sugarcane. It is classified as biocompostable because, under certain environmental conditions, it can be hydrolyzed to l-lactic acid, thus qualifying it as one of the biodegradable polymers.

Q: What factors affect degradation of PLA polymers?

A: The degradation of PLA virtually is conditioned by the degradation conditions of temperature, moisture and pH. The hydrolysis of PLA occurs more swiftly in the humid and hot temperature range.

Q: Does the molecular weight of PLA influence its biodegradation processes? If yes, how?

A: It has been observed that high molecular weight PLA is more resistant to fast degradation than low molecular weight PLA. This is because d-lactic acid and l-lactic acid molecules found in the short pla chain require a shorter time to degrade during the process than the long pla chain molecules.

Q: Is it possible to recycle PLA and how can one do this?

A: Right, PLA may be recycled but the procedure involved is not the same as those for other plastics. It requires collection and sorting of the PLA products, followed by a process wherein PLA is degraded into monomers in a controlled environment and can then be produced into new PLA products.

Q: What are the various degradation techniques employed on PLA?

A: Hydrolytic degradation, thermal degradation, and biodegradation are the different degradation techniques developed for PLA. Each approximation employs a unique set of conditions to decompose the structure of PLA.

Q: How long does one have to wait for PLA to decompose?

A: Variance in degradational time frame for PLA is instigated by environmental factors and degradation parameters. For instance, In industrial composting facilities this material may take approximately 6 months to degrade while in natural circumstances it may take years.

Q: Is there any area in the medics where PLA can be used?

A: PLA is applied in the medical field, including sutures and screws and plates because it is biocompatible and safe to be absorbed by the body. The rate of the degradation kinetics is crucial so as to allow the PLA to be metabolized in a uniform manner.

Q: How does crystallization affect the degradation of PLA?

A: The rate of crystallization of PLA affects its mechanical properties and rate of degradation. Crystalline form of PLA has slower degradation rates in the presence of water while the amorphous form shows higher rates of degradation.

Q: Can you elaborate on the differences which exist between in vitro done in the lab versus in vivo done in the body.

A: The researchers who conducted the in vitro experiment have stated that the fact that it is done in a controlled laboratory environment may affect PLA degradation rate than the in vivo which is done on human. In vitro yes, you may modify many things about the environment like the temperature, pH, and enzymes that can influence the degradation of PLA.

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