Over the last two decades, the Chinese automotive market has undergone exponential growth. The perception of smell differs in this market from others and customer complaints about unpleasant interior odors have also grown to such an extent that it is still considered the OEM´s number one challenge in this respect.
Car interior odor issues have consistently been the most complaint in the Chinese automotive market.
Source: J.D. Power 2020
There are many explanations for this phenomenon apart from the perceptual differences related to culture. Due to increasing environmental pressures to reduce water and energy consumption this has led to less washing and lower drying temperatures leading to higher “residuals” in the leather. Furthermore, the increasingly demanding automotive requirements, especially regarding high heat fastness, has led the move away from certain natural products towards synthetic alternatives and, therefore, the typical leather smell has consequently changed.
Perceptual influences based on culture simply cannot be changed. We also cannot reliably measure smell by objective test machinery. Collectively this means that this odor issue presents an exceptionally difficult challenge to tackle in advance of the complaint. In other words, it is likely that this will remain an ongoing challenge.
From where does the sources of “bad” leather smell come from? There are many sources, but mainly they originate from four main ones:
The Chinese automotive market is very critical about smell emanating from fatliquors, commonly associated to an “animalic” odor. No matter which type of natural raw material is used, over time it starts oxidizing and, therefore, releases a distinctive smell.
LEVOTAN® HPP is an odorless softening polymer designed to replace fatliquors and completely avoids the typical “animalic” smell source. LEVOTAN® HPP does not contain these problematic materials and due to its chemistry possesses extremely high heat fastness performance (no oxidation) and thus zero impact on smell.
Test Report: TA 220204, Date: 20.06.2022 I Customer: TFL – Huningue I Title: Screening – Smell
Determination of the odor characteristics of trim materialsin motor vehicles according to VDA 270
TFL France, S.A.S, Testing Lab, Sabine Dickhaut-Guedemann. The results are only valid for the samples tested in TFL.
Over the last two decades automotive heat yellowing requirements have steadily increased. Why?This is mainly due to two key reasons:
The speed of internal car temperatures increases is given in the below chart. For example: If the outside air temperature is 35°C, in just one hour the car interior can reach 59°C but after two hours, it could reach up to 120°C depending upon the prevailing ambient conditions.
Therefore, the standard natural chemicals used in traditional processes such as vegetable tanning agents or animal oil based fatliquors were replaced by synthetic ones, in order to reach the demanding heat resistance requirements. However, due to this shift, the well-known “natural leather smell” has, as a consequence, disappeared.
Japanese automotive manufacturer TOYOTA started to request high heat yellowing performing articles measured by their test method TSL5101G 3.23 using the conditions of 110°C for 400hrs. The specifications for finished leather use the GS (Grey Scale) and a Grade >4 and Delta E must be <3.8 with no extraordinary change.
HONDA, on the other hand, use heat resistance test method JIS L 0804 / 8102 that is performed in a bottle (250 cm3) with the test conditions of 110°C for 200hrs and 120°C for 120hrs. Specifications for finished leather use the GS and a Grade >4 with slight change but not evident and Delta E specification of <2.0.
From the formulation point of view, it is very important to select a suitable wet-blue or wet-white from the outset, especially with an acceptably low content of residual natural fat content. However, from the chemical point of view, the major source of poor heat yellowing values are the natural based fatliquors and certain synthetic tanning agents that, although may have a very good whitening effect, may be susceptible to yellowing on exposure to heat (see pictures on the following page).
The chemistry of LEVOTAN® HPP achieves the highest heat yellowing requirements giving the possibility to combine or to replace 100 % of the standard automotive fatliquors depending on the article required, chrome or chrome-free.
The partial replacement of synthetic tanning agents is also possible by using the right balance between acrylic polymers (e.g., MAGNOPAL® and/or LEUKOTAN® range) combined with protein fillers such as SELLASOL® FSU.
The application of LEVOTAN® WS in combination with, for example, LUBRITAN® GXL can impart to the leather excellent softness and tightness after the milling process, especially with chrome-free material.
LEVOTAN® HPP is a biodegradable, compostable and yet oxidation resistant (fatty acid-free), the odorless polymer. It also possesses extreme fastness under heat and light exposure without the risk of Chrome VI formation.
As fatliquoring has a strong impact on these requirements, LEVOTAN® HPP was specially designed to replace up to the complete offer of natural based fatliquors and confer excellent performance on automotive articles such as fogging gravimetric, reflectometric and haze, as well as extremely low emissions and COD values.
Leather treated with LEVOTAN® HPP is compostable.“Compostable materials are those that degrade by biological processes to yield CO2, water, inorganic compounds and biomass at a rate consistent with biodegradation of natural waste while leaving no visually distinguishable remnants or unacceptable levels of toxic residues.” (ASTM International 2012).
Table 1: Wet White Leather degradation residues after 90 days completion of the thermophilic part immediately followed by 90 days of mesophilic part of compostability test according to ISO 20200.
Test done by Authenticae Ltd.
Fig.1. FOC Leather with LEVOTAN® HPP (a) at the beginning of the test, (b) degradation residues after 180 days completion of the ISO 20200 compostability test (values are given in cm).
Levels of toxic chemicals after thermophilic part (90 days) show very little concern for leather sample.
(1) TgFM is the total top growth fresh mass of plant at 28 days. (2) is the mean top growth fresh mass per plant at 28 days.
Fig.2. Plant growth after 28 days in compost containing (A) FOC leather without LEVOTAN® HPP; (B) FOC leather with LEVOTAN® HPP. Comparison with blank and control without leather.
The two test samples (FOC leather with and without LEVOTAN® HPP) grew less than the Blank and control samples in top growth, and in plant height indicating that LEVOTAN® HPP do not significantly impact plant growth behavior.
LEVOTAN® HPP is a new generation of softening polymers, taking care of the latest environmental standards and specifically designed to meet the highest automotive requirements.
Heat and light fastness