Application Note. Rapid Quality Control of Nitrile Rubber (NBR) Batches Using the IVA Versa Intrinsic Viscosity Analyzer

By Polymer Char, Valencia, Spain. 
F. Cordero, A. Cárdenas, N. Fernández

Rapid Quality Control of Nitrile Rubber (NBR) Batches Using the IVA Versa Intrinsic Viscosity Analyzer

1. Introduction

Acrylonitrile–Butadiene Rubber (NBR) is a key elastomer used in the production of disposable gloves, medical devices, seals, and industrial components that demand excellent oil and chemical resistance. However, batch-to-batch variability in raw materials can lead to critical production issues, such as inconsistent viscosity, reduced elasticity, poor film uniformity, and decreased puncture or tensile strength in finished gloves and other medical products.

Traditionally, molecular weight characterization of NBR is performed by Gel Permeation Chromatography (GPC) at room temperature with triple detection. Although accurate, this method is time-consuming, solvent-intensive, and requires highly trained operators for both operation and data interpretation, making it unsuitable for rapid quality control environments. Other advanced techniques such as Dynamic Mechanical Analysis (DMA) and Nuclear Magnetic Resonance (NMR) are also used for structural evaluation of NBR microstructure but are expensive, complex, and difficult to implement in routine quality control workflows¹.

The IVA Versa (Polymer Char) offers an alternative, providing fast, reliable, and automated intrinsic viscosity (IV) measurements that correlate directly with the molecular weight average through the Mark–Houwink relationship². This technique reduces solvent use, simplifies operation, and provides results suitable for real-time decision-making in production and QC environments.
 

2. Materials and Methods

A glove manufacturer reported significant variations in the quality of NBR lots supplied by a raw material vendor. These inconsistencies affected processing stability and final product performance, generating downtime and waste in glove production lines.

Two NBR samples were analyzed:

• NBR–Reference (NBR-Ref): Good-quality batch supplied by the vendor.
• NBR–Low Quality (NBR-LQ): Batch showing inconsistent behavior during glove production.

2.1 FTIR-ATR Characterization
Both samples were first characterized by FTIR–ATR to assess their chemical profiles and confirm the presence of nitrile and butadiene functional groups, as well as potential additives or contaminants that could influence performance.

2.2 Intrinsic Viscosity Analysis (IV)

Intrinsic viscosity (IV) was determined using the IVA Versa instrument under the following conditions:

The analysis follows ISO 1628-1:2024⁴. Data processing was performed using the Solomon–Ciutà equation to calculate IV directly from the viscometry signal. The Mark–Houwink parameters for NBR in THF at 25 °C were used (K = 4.95 × 10⁻⁴ dL/g, α = 0.689)2 to estimate the viscosity-average molecular weight (Mv).

3. Results and Discussion

3.1 FTIR analysis:

The FTIR spectra of both samples exhibited the characteristic absorption bands of NBR, including the –C≡N stretching around 2238 cm⁻¹ and the C=C vibrations near 1640 cm⁻¹. The sample identified as NBR–Low Quality presented minor variations in the baseline and no additional signals associated with residual additives or oxidation products, indicating no compositional differences or partial degradation³. This characterization confirms that both samples are diluted in water according to the typical infrared bands for this solvent.

Figure 1. FTIR-ATR NBR Spectra

3.2 Intrinsic Viscosity Analysis (IV):

The IV results obtained from triplicate measurements are summarized in Table 2:

The low RSD values (< 2%) confirm the excellent repeatability and robustness of the IVA Versa technique⁴. A difference of nearly 60% in intrinsic viscosity between the two batches was observed, corresponding to a significant reduction in molecular weight for the NBR-LQ. This correlates with lower viscosity, weaker mechanical strength, and poorer film formation observed during glove manufacturing.

Compared with traditional NMR, DMA or even GPC analysis at room temperature, which can take several hours per sample and requires liters of solvent², the IVA Versa provided quantitative molecular information within minutes, using minimal solvent and with no sample degradation. The system’s automation and small footprint make it ideal for on-site QC implementation, eliminating the need for highly trained personnel or complex data interpretation.

Fig. 2.- Intrinsic Viscosity plot comparison between NBR Samples

4. Conclusions

The IVA Versa demonstrated its capability to rapidly and accurately differentiate between high-quality and problematic NBR batches through intrinsic viscosity measurements. Key advantages include:

• Fast sample quality screening.
• Completely automated operation, freeing analysts for other tasks.
• Low solvent consumption (near to 40 mL per sample) and minimal maintenance requirements.
• High repeatability and robust correlation with molecular weight via the Mark–Houwink relationship.
• No thermal or chemical degradation of the sample, preserving material integrity.

The observed ~60% difference in IV between good and poor-quality batches (NBR-Ref and NBR-LQ, respectively) provides a clear and quantitative basis for immediate quality control decisions. No significant differences were observed between the FTIR-ATR spectra of both batches. However, a clear and substantial difference was found in the IV results, demonstrating that this technique provides quantitative values suitable for rapid decision-making in production and quality control environments. Higher variability in viscosity among different replicates indicates a lack of homogeneity, which can also lead to problems in the finished products. Thus, the IVA Versa represents a cost-effective and reliable alternative to other high-end techniques for rapid molecular characterization of NBR in production and QC environments.

5. References

1. Entanglements, Defects, and Inhomogeneities in Nitrile Butadiene Rubbers: Macroscopic versus Microscopic Properties (2016)., Imran Hussain Syed. ASC/Macromolecules, Vol 49, Issue 23.
2. Determining the Mark–Houwink parameters of nitrile rubber: a chromatographic investigation of the NBR microstructure (2013). Polym. Chem., 4, 4755-4767.
3. Improving Thermo-Oxidative Stability of Nitrile Rubber Composites by Functional Graphene Oxide (2018). Rui Zhong, Materials-11-00921. doi:10.3390/ma11060921
4. ISO 1628-1:2024 Plastics – Determination of the viscosity of polymers in dilute solution using capillary viscometers – Part 1: General Principles

This application note was developed in collaboration with a NBR glove manufacturing company in Biyagama, (Sri Lanka), which has supplied the samples and some results for this study.