The question, if magnesium oxide can be used as alternative to zinc oxide in vulcanization is becoming increasingly relevant for the rubber industry. For decades, zinc oxide is an established component of sulphur-based systems and plays a pivotal role in the cross-linking process. However, at the same time, there is a growing pressure to evaluate its use more closely from both an environmental and a process perspective.
For developed departments this does not result in a simple yes or no decision, but rather leads to a more multi-faceted question: Is the goal a complete replacement of the product or rather a targeted adaptation of the existing systems?
Overview: Zinc oxide vs. Magnesium oxide
A direct comparison of the two raw materials helps in painting an initial picture:
| Property | Zinc oxide (ZnO) | Magnesium oxide (MgO) |
| Molecular formula | ZnO | MgO |
| Cost | high | low |
| Role in vulcanization | Standard activator | Supplementary raw material / Sub-stitute component |
| Industrial Use | Well established | established, but less dominant |
Zinc oxide is known on the market by various synonymous names including zinc white and ‘Flowers of Zinc’. It is classified under two main grades: the EP grade for regular applications in pharmaceuticals and cosmetics and technical grades for industrial applications.
For a more in-depth look at magnesium oxide as a raw material, we would like to refer to our Mineral-Insights article. Also for this raw material, various grades are available in the market.
This article focuses on the technical qualities, as these are relevant to applications such as vulcanization and a variety of similar applications.
Why Zinc oxide should be reevaluated
Zinc oxide plays an important role in various fields; hence it makes total sense to deep dive and assess through its entire life cycle. Environmental aspects are particularly receiving focus, for example in connection with aquatic systems or the release of zinc oxide during its usage and disposal phase.
From process standpoint too, handling finely divided oxides is not a trivial matter. Factors such as particle behavior and exposure must be considered for certain applications. The resulting consequence is not a complete abandonment of zinc oxide but rather a clear trend to move towards more informed formulation decisions.
How to evaluate the Substitution Potential of Zinc Oxide as an Example
An interesting approach would be a methodological analysis. To differentiate between raw materials not only qualitatively but also in a structured manner, simple evaluation methods are used in the early stages of development. A widely known method is the approach developed by Biwer and Heinzle (2004). This evaluation is further carried out below. Some of the most important points taken into consideration in the process are stated below.
The core method involves a standardized classification of various criteria such as toxicity, environmental impact, and resource requirements. Each parameter is rated on a three-point scale: critical (A=3), neutral (B=2), and non-critical (C=1).
What may sound abstract at first quickly becomes tangible in practice. A simplified example illustrates this:
| Impact Category | Zinc oxide | Zinc oxide Score | Magnesium oxide | Magnesium oxide Score |
| Acute toxicity (oral) | C | 1 | C | 1 |
| Acute toxicity (inhalation) | A | 3 | C | 1 |
| Skin Irritation | C | 1 | C | 1 |
| Eye Irritation | A | 3 | C | 1 |
| Sensitization | C | 1 | C | 1 |
| Chronic Toxicity | A | 3 | C | 1 |
| Aquatic Toxicity | A | 3 | C | 1 |
| Persistence | A | 3 | C | 1 |
| Bioaccumulation | C | 1 | C | 1 |
| Acidification Potential | C | 1 | C | 1 |
| Eutrophication Potential | C | 1 | C | 1 |
| Photochemical Ozone Creation Potential (POCP) | C | 1 | C | 1 |
| Global Warming Potential (GWP) | C | 1 | C | 1 |
| Air Pollutions/ Dust Emissions | A | 3 | A | 3 |
| Resources and Energy Requirements | A | 3 | C | 1 |
| Total Score | 29 | 17 |
If we now divide the total score by the number of categories we have evaluated (15 categories), we get a total score of 29 and 17 respectively and an average value of 1.93 for zinc oxide and 1.13 for magnesium oxide. This magnesium oxide is very close to the ideal value of 1 and hence can be considered safe. In a direct comparison, zinc oxide posses a higher potential risk.
This finding requires a careful consideration: it highlights the differences between the two mineral raw materials but doesn’t provide an absolute indication of ‘good’ and ‘bad’. This is precisely where the strength of the method lies. It provides guidance without oversimplifying the complexity of real-world applications. It is therefore necessary to incorporate further methodological expertise to finalize the evaluation of a potential substitution for zinc oxide.
Role of Magnesium oxide in vulkanization
Against this backdrop, the key question is what role magnesium oxide can realistically play in existing systems.
In practice, it has been shown that magnesium oxide is rarely used as a complete substitute. Rather, it opens possibilities within the formulation. These can be broadly categorized into three areas:
- Magnesium oxide can be used to intentionally reduce the proportion of zinc oxide in a formula. This doesn’t completely replace the function of zinc oxide, but it adjusts the overall amount.
- Magnesium oxide has fundamental chemical properties, like its basic character. This means it can take on additional roles in certain systems, for example in stabilizing processes.
- Using magnesium oxide also always changes the overall logic of the formula. It’s not an isolated swap, but an adjustment within the system.
What this means for the formulation strategy?
The central insight can be formulated clearly:
A universal 1:1 substitution of zinc oxide with magnesium oxide is generally not effective. More value arises where both raw materials are considered in the context of the specific application. What really matters is the interplay of:
- Requirements of the final product
- Behavior in the process
- And aspects such as environment und regulatory
In many cases, this approach leads to mixed or transitional solutions not out of compromised thinking, but because they make sense technically. It becomes clear that a combination of zinc and magnesium oxide could possibly be beneficial in terms of the manufacturing process, the product, or even on its environmental impact.
Integration in practical applications
Zinc oxide remains a central component of many established systems. Especially in cases where stable and reproducible properties are required, there are good reasons to adhere to existing formulations.
Magnesium oxide, on the other hand, offers the possibility to further develop these systems. It provides options without completely leaving the familiar framework. This is precisely where the real leverage lies: not in replacing, but in deliberately rethinking existing solutions.
Summary
Usage of magnesium oxide as an alternative to zinc oxide in vulcanization is not a simple substitution issue, but rather a tactical-strategic question of product development.
This example demonstrates that zinc oxide remains functionally relevant. At the same time, however, it shows that magnesium oxide opens more possibilities and avenues to reassess formulations in vulcanization applications.
Furthermore, it can be inferred that magnesium oxide can also be purposefully used in combination with other mineral raw materials in additional areas, such as the refractory industry, the chemical industry, or in environmental technology applications.
The deciding question is hence not that which raw material is better? Rather: Which combination delivers the best overall result for the specific process or product in each case?
We support you in developing specific formulations for your applications. For the specific case, we have, among our large pool of products, the following magnesium oxides in our portfolio:
MAGNESIA 295
Magnesium oxide
- Heavy
- Very highly active
MAGNESIA 2933
Magnesium oxide
- Heavy
- Highly active
MAGNESIA 2923
Magnesium oxide
- Heavy
- Active
MAGNESIA 2925
Magnesium oxide
- Heavy
- Active
MAGNESIA 291
Magnesium oxide
- Heavy
- Medium active
