What do plasticizers do to polymers

Embrittlement testing is one way we can determine if a plasticizer has leached from a polymer, causing a material to behave in an unexpected and undesired way. Leaching is one of the most common challenges in working with plasticizers. When a plasticizer leaches from a polymer, the material can become rigid and breakable, and product contamination could occur from the leached material, which is not a good thing. Skip to content. Phthalates are used in PVC cables, films, coatings, adhesives and certain plastics that need flexibility.

Dicarbonates are also used in PVC when the application needs to work in low temperatures. The NBR sample initially contains 11 wt. By choosing a high ratio, e. The lower the ratio, the more evaporation-controlled the system is and the more S-shaped the plasticiser loss is on a square root of time basis, Fig. The evaporation coefficient can be estimated for the evaporation-controlled case by assuming that the initial part of the mass loss is mainly due to evaporation.

By fitting the initial mass loss data as a function of time to a polynomial function, and knowing the plate surface area, F can be estimated. Then, a different relationship, where the actual concentration profile is not used in the boundary condition, can be adopted. One example is:. Desorption of a plasticiser from a 1-mm-thick plate plotted as a function of a square root of time and b time. The corresponding concentration profiles are shown in c diffusion-control, d evaporation control and e switch from an evaporation- to a diffusion-controlled mode.

The arrows denote increasing times. The effects of a plasticiser concentration-dependent diffusivity on the plasticiser migration kinetics are illustrated in Fig. The modelling was made with Eq. The characteristic features are a small initial deviation from a linear loss on a square root of time basis, hardly observed in the figure , indicative of an evaporation-controlled mode and a slow plasticiser loss at a late stage due to a diffusion-controlled mode.

Consequently, the plasticiser concentration profile is initially relatively flat and at later stages shows a stronger concentration profile near the surface. Both fits agreed well with the experimental data up to a certain mass loss, where after using a concentration-dependent diffusivity yielded a better fit.

It should be noted that with the obtained plasticisation power of 8. In cases where the plasticisation effect is large the difference in the mass loss curve between the two cases will be larger.

Drawn after experimental data in ref. Another example where the plasticiser loss displays an essentially linear relationship with the square root of ageing time in the diffusion-controlled mode is illustrated in Fig. In such a system, there is a film of plasticiser that forms on the sample surface see below. The shape of the concentration profiles has often been used to determine if a system is evaporation- or diffusion-controlled.

Figure 5 shows the profiles of plasticiser concentration in an EPDM rubber as a function of time at two temperatures. Drawn after data in ref. Drawn after data of ref. For a case where the plasticiser has a very high boiling point e. However, Ekelund et al. Smith et al. Surface blooming due to crystallisation and bleeding are effects of the deposition of migrated components on the surface. The surface of PVC floors tends to become sticky with time, which is caused by the formation of a plasticiser layer on the surface bleeding.

Figure 1c also clearly shows the formation of a plasticiser film on the NBR surface in the evaporation-controlled mode. By using sum frequency-generation vibrational spectroscopy, Zhang et al. Bellobono et al. Ljungberg et al. As shown in Table 1 , evaporation is, in general, the rate-limiting process for plasticiser migration at lower temperatures, whereas diffusion is the limiting process at higher temperatures.

Hence, the temperature-dependence is stronger for the evaporation process than for the diffusion process. Schematic of the Arrhenius plot for the kinetics rate parameter k controlled by evaporation below T c green line and by diffusion above T c blue line.

The red line and data points in regions A and B represent the overall migration rate of a plasticiser from a polymer. The data points in region C represent the evaporation rates of plasticiser from the pure liquid.

The plot is simplified and limited to the following special cases: 1 the diffusivity in the plot is taken as the average of the concentration-dependent diffusivity, 2 the system exists above the glass transition for all plasticiser concentrations, and 3 the temperature and plasticiser concentration effects on the diffusion and evaporation activation energies are not considered.

With the exception of temperature, other factors can affect the actual migration mode, especially when the ageing temperature is close to T c. Royaux et al. Audouin and Verdu 30 observed that both the initial plasticiser concentration and the plasticiser size play important roles in determining the dominant mode.

They observed that the evaporation-controlled mode dominates for large plasticisers and high initial plasticiser concentrations and consequently, that the diffusion-controlled mode dominates for small plasticisers and low initial plasticiser concentrations. The authors also showed that the migration kinetics of both didecyl phthalate and dinonyl phthalate from PVC were controlled by evaporation when the concentration was higher than 20 wt.

This agrees with the fact that the diffusivity is plasticiser concentration-dependent and decreases with the concentration Eq. In addition, a smaller concentration gradient at low plasticiser concentrations also contributes to the dominance of the diffusion-controlled mode.

Their results indicate that in some cases, such as for the migration of plasticiser from samples with a high initial concentration of plasticiser, it is possible to observe both modes during ageing where the migration is at first controlled by diffusion and then switches to become controlled by evaporation when the concentration of plasticiser decreases beyond a critical level.

In addition, inorganic fillers e. As a result, the incorporation of fillers into commercial products of plasticised plastics is not so common or the filler is used in a small concentration. As an example, the outer layer of a fuel pipe made of plasticised polyamide 12 only contains 0. They explained that this was caused by a strong interaction between the plasticiser and carbon black. The situation is different in rubbers where a large amount of carbon back is often used in combination with plasticiser.

However, the effects of carbon black on the plasticiser diffusion have not been investigated separately. The type of plasticiser migration mode is traditionally determined by analysing the shape of the plasticiser desorption curve or the concentration profile within the sample.

The curves of the mass loss versus ageing time or the square root of ageing time are commonly obtained by intermittently measuring the mass loss as a function of time using an analytical balance or by measuring the remaining plasticiser concentration inside the sample. The plasticiser concentration in polymers can be measured by thermogravimetry and infrared spectroscopy IR 30 directly, or by extracting plasticiser with solvents, followed by measuring the plasticiser concentration in the extracted solution with chromatography.

However, in the diffusion-controlled mode, the same measurement underestimates the average sample plasticiser concentration due to the existence of a concentration gradient towards the surface. In cases where it is not possible to monitor the plasticiser loss over time, the shape of the plasticiser concentration profile at a single ageing time can be used to reveal the migration mode.

Slicing is the most common method used to profile the plasticiser concentration. Additionally, in a recent study conducted by Adams et al.

The expected lifetime of polymer products can be as long as several decades and for prediction purposes, the migration process needs to be accelerated by ageing samples at high temperatures. The plasticiser loss can then be predicted by extrapolating the obtained data at high temperatures to service temperatures. Studies have shown that both the plasticiser evaporation and diffusion processes obey the Arrhenius law, which indicates that the Arrhenius law is valid for the extrapolation.

Hence, when considering large plasticiser concentrations and temperature intervals, this should not be ignored. Due to the existence of the two rate-dominating modes, accelerated ageing needs to follow the same migration mode as the actual service conditions. For instance, the highest accelerating temperature should be lower than T c for the actual case controlled by evaporation. This requires the determination of the temperature regions for these two modes before selection of the accelerating temperatures.

Overlooking the existence of these two modes can lead to a false prediction. As shown in Fig. The plasticiser loss is typically controlled by the evaporation process at low temperatures, i. This makes the prediction easier since the evaporation process is independent of the glass transition temperature of the polymer and the plasticiser concentration within the polymer product, but it depends on the evaporation characteristics of the plasticiser.

For this case, a database of the evaporation rates of common plasticisers at different temperatures and their activation energies is useful for prediction purposes. However, this type of database covering various common plasticisers is currently not available. As mentioned above, the evaporation rate of a plasticiser from the polymer is similar within an order of magnitude to that from its liquid state when a plasticiser film forms on the surface.

The evaporation rate should be possible to estimate by using the evaporation rate data for the pure plasticiser directly.

In this approach, the temperatures for accelerated testing can be greater than T c , as illustrated by the extrapolation of the data points in region C in Fig. However, it is important that the high temperatures chosen for accelerated ageing should not cause any degradation of the plasticiser.

Ekelund et al. In addition, other ageing processes, such as the oxidation and annealing of polymers, are also accelerated at high temperature. In some cases, a plasticised-polymer product, such as a polyamide-based fuel pipe in a car, may experience high temperatures during service and diffusion-controlled migration.

Plasticisers are increasingly used in a wide range of biopolymers to mainly improve their poor processability and make them more ductile and tougher. Studies have shown that the migration behaviour of plasticiser in biopolymers is often complex.

The cold crystallisation of biopolymers, such as PLA 38 , 54 , 55 , 56 and starch 57 , 58 , is accelerated in the presence of plasticisers, 59 which increases the crystallinity and then the plasticiser concentration in the amorphous region.

This, in turn, affects the plasticiser diffusion properties during ageing. To avoid the deterioration of polymer materials caused by plasticiser loss, several approaches have been used to hinder plasticiser migration.

The most common way is to increase the molecular size of the plasticiser, which can be achieved by using polymeric plasticisers and oligomers, 64 , 65 and branched and star-shape plasticisers. However, plasticisers with a larger molecular size have a lower plasticising efficiency than most traditional plasticisers. In addition, surface modifications, such as surface coatings and crosslinking, are commonly employed to suppress plasticiser migration.

In this paper, we discuss plasticiser losses from plastics and rubbers, losses which lead to inferior product properties, bleeding and eventual pollution of the surrounding environment. The loss to the surrounding gas phase occurs through diffusion inside the material to the surface and through evaporation from the surface.

The loss is either diffusion- or evaporation-controlled, where the former usually occurs at high temperatures and the latter at low temperatures. In the evaporation-controlled mode, a film of plasticiser is often formed at the surface, which is indicated by a linear loss with time, at least over a certain time period.

In addition to the temperature, the actual mode that dominates depends on several factors, including the plasticiser and polymer characteristics, product geometry and specific environment. The fact that the plasticiser diffusivity is plasticiser concentration-dependent can lead to a shift in the loss-mode from diffusion to evaporation control at otherwise constant conditions.

It is also shown here how it is possible to determine which mode limits the loss and the ways to extrapolate accelerated migration tests to service conditions. Warnings are also given that meaningful extrapolation and prediction of plasticiser migration requires consideration of several important factors.

We also highlight issues with new emerging systems with bio-based plasticisers in biopolymers. The data that support the findings modelling results of this study are available from the corresponding author upon reasonable request. Rahman, M. The plasticizer market: an assessment of traditional plasticizers and research trends to meet new challenges.

Wypych, G. Handbook of Plasticizers. ChemTec Publishing, Vieira, M. Natural-based plasticizers and biopolymer films: a review. Mekonnen, T. Studies related to how they affect the environment, whether phthalates permeate indoor dust, and whether endocrine disruption from phthalate exposure is a factor to be concerned with, have all been performed. The Registration for Evaluation, Authorisation, and Restriction of Chemicals REACH , which is known to be the mots comprehensive and strict safety regulating organization in the world, has determined that nearly all plasticizers are safe, and so has the FDA.

We take pride in designing and manufacturing all types of custom plastics while offering a short lead time and low per-unit cost. If you would like to learn more about our injection molding and thermoforming, reach out to our team today. Automated page speed optimizations for fast site performance. What Is a Plasticizer?

Four Families of Plasticizers Over 30, substances have been tested for use as a polymer plasticizer, though today, only about 50 are available for use. Of these, they are divided into four families: Phthalates, which are used for flexibility in plastics Dicarbonates are used in shaping PVC at lower temperatures; Phosphates are used to make a material flame retardant.