Benefits PP vs. Other Materials Taste and Odor How It Works

 Taste and Odor

Organoleptics of 2nd Generation Clarifiers
Three generations of sorbitol based clarifying agents are available for polypropylene (PP). When added to polypropylene, the second generation clarifying agents, para-substituted dibenzylidene sorbitols (MDBS or EDBS), improve the haze and clarity over the now obsolete first generation products (dibenzylidene sorbitol or DBS). However, 2nd generation products have a severe limitation due to poor organoleptics. Organoleptics is how the human sensory organs perceive the taste, odor, and texture of a substance. In polypropylene, MDBS clarifying agents exhibit a distinctive cherry, almond odor. More importantly, it is now known that this odor readily transfers odor and taste characteristics to contacted goods (such as food, clothing, and the like). This undesirable quality prevents the use of MDBS in most container and packaging applications. Even in non-container applications, clarified PP resins containing MDBS generate a distinctive odor during processing, so the risk of worker complaints is created at PP molding and fabricating plants.

Chemistry of Taste and Odor Production in MDBS
The distinctive cherry, almond taste and odor transfer property of MDBS is caused primarily by p-methyl benzaldehyde. Our research has shown that the presence of trace quantities of this chemical in an MDBS product can be explained by three different mechanisms. First, the aldehyde may be formed through oxidation of MDBS at high temperature. Production by this method can usually be deterred through the addition of antioxidant to the resin formulation. Second, the aldehyde may be residual raw material from the manufacturing process. Many attempts have been made to eliminate residual aldehyde through thorough careful purification of the MDBS. However, trace contamination is practically impossible to prevent, and the threshold detection level of the aldehyde by human sensory organs is in the parts per billion range. Finally, and perhaps the most important of all, the aldehyde contaminant is formed naturally in MDBS by heating at relatively low temperatures such as those during typical compounding or molding. This type of chemical degradation (intramolecular rearrangement followed by elimination of the aldehyde) leads to the generation of trace quantities of aldehyde sufficient to cause the taste and odor problems. This chemical degradation process is inevitable and unavoidable during melt processing.
 

Organoleptic Testing -- Comparison of Millad 3988 to Commercial MDBS Grades
Organoleptics of sorbitol based clarifying agents in PP are objectively evaluated by Milliken Chemical, using standard test procedures, based on general guidelines established in ASTM STP 434 (Manual on Sensory Testing Methods) and ASTM STP 758 (Guidelines for the Selection and Training of Sensory Panel Members).

Water samples for organoleptics testing are prepared in the following manner: The clarifying agents to be tested are compounded in polypropylene using a standardized formulation containing adequate loadings of an antioxidant package and acid scavenger. The resin is injection molded into 2x 3x 0.050 in. specimens and six plaques from each set are placed in clean glass jars with glass pipettes as spacers to maximize surface area. The jar is filled with 720 mL of pure water, securely sealed, and placed in a convection oven at 50°C for five days. The water samples are chilled prior to random, double-blind paired comparison evaluation by a carefully screened taste panel.

Taste panel results comparing Millad 3988 to commercial grades of MDBS are shown below. In each test, eleven panelists were blindly presented water samples from each clarifier in random pairs. Pure water is used by each panelist to cleanse the palate before each sample is tasted. The panelists are asked to rate a pair of samples in the order presented on the basis of the least taste. Using this format, a difference of nine panelists choosing one preference for a given pair indicates a statistical difference at the 95% confidence level.

The results clearly indicate Millad® 3988 to have superior organoleptics to all commercially available MDBS clarifying agents.