Influence of Thermally-Accelerated Aging on the Dynamic Mechanical Properties of HTPB Coating and Crosslinking Density-Modified Model for the Payne Effect.

Yongqiang Du,Jian Zheng,Guibo Yu

doi:10.3390/polym12020403

Abstract

Hydroxyl terminated polybutadiene (HTPB) coating is widely used in a solid rocket motor, but an aging phenomenon exists during long-term storage, which causes irreversible damage to the performance of this HTPB coating. In order to study the effect of aging on the dynamic mechanical properties of the HTPB coating, the thermally-accelerated aging test was carried out. The variation of maximum elongation and crosslinking density with aging time was obtained, and a good linear relationship between maximum elongation and crosslinking density was found by correlation analysis. The changing regularity of dynamic mechanical properties with aging time was analyzed. It was found that with the increase of aging time, Tg of HTPB coating increased, Tα, tan β and tan α decreased, and the functional relationships between the loss factor parameters and crosslinking density were constructed. The storage modulus and loss modulus of HTPB coating increased with the increase of aging time, and decreased with the increase of pre-strain. The aging enhanced the Payne effect of HTPB coating, while the pre-strain had a weakening effect. In view of the Payne effect of HTPB coating, the crosslinking density was introduced into Kraus model as aging evaluation parameter, and the crosslinking density modified models with and without pre-strain were established. The proposed models can effectively solve the problem that the Kraus model has a poor fitting effect under the condition of small strain (generally less than 1%) and on the loss modulus, which have improved the correlations between the fitting results and the test results.

Highlights

A polyurethane network system based on hydroxyl terminated polybutadiene (HTPB) has been widely used in composite solid propellant, adhesive, sealant, coating, and so on, because of its convenient processing and good mechanical properties [1]
Elongation maximum elongation of HTPB coating decreased with the increase of aging time, and the decreasing
The change of the crosslinking density of HTPB coating was the results of postd curing, had exceeded

Summary

Introduction

A polyurethane network system based on hydroxyl terminated polybutadiene (HTPB) has been widely used in composite solid propellant, adhesive, sealant, coating, and so on, because of its convenient processing and good mechanical properties [1]. As a molecular structure parameter, crosslinking density affects or even determines the mechanical properties of the material, such as tensile strength, elongation, modulus, compression deformation, swelling rate, hardness, etc. Compared with the macro-mechanical properties (such as elongation, strength, etc.), crosslinking density is more suitable for being the aging evaluation parameter of HTPB coating [2,3]. Katarzyna et al [5] found that the existence of crosslinking resulted in the increase of the glass transition temperature Tg. the linear relationship equation between Tg and crosslinking density was derived in the study of Fox and Loshaek [6]. The mainly aging reaction was oxidation crosslinking, and the change of crosslinking density affected the mechanical properties of the material. Byungwoo et al [11]

Methods

Results

Conclusion