Effects of moisture on aging of polymer composite materials in a cold climate

The Influence of Internal Stresses on the Aging of Polymer Composite Materials: a Review

“…The main result of the action of internal stresses in combination with environmental factors is the formation of additional microfaults in the form of transverse cracks in PCM layers and destruction of the interface of polymer-reinforcing filler [19]. Microcracks and delamination worsen the mechanical properties of PCMs, which has been proven by numerous studies [19,[23][24][25][26].…”

“…Therefore, to clarify the effect of internal stresses on the aging of PCMs, it is important to analyze the thermal cycling of moisture-saturated PCMs. A comparison of the research results obtained in [23,56,57] shows that, if the thermal cycling is carried out in the range of positive and negative temperatures, wet PCMs deteriorate their mechanical characteristics with a higher probability than dry ones. This process is facilitated by the internal stresses caused by both swelling (7), (8) and transition to the glassy state of water in the free volume of polymer matrices by the mechanism considered in [58].…”

“…The examples considered illustrate the noticeable effect of internal stresses on changes in the mechanical parameters of PCMs at the initial stages of aging (thermal [24, 25, 53-55, 66, 74], thermal and humid [25,[61][62][63][64][65]67], climatic [8][9][10][11][12][13][14][15][16][17], [23,27], and in open space [72]), when the threshold number N 0 of thermal cycles was exceeded. However, due to relaxation of internal stresses at later stages, a certain limiting state of physicochemical transformations and microfaults is reached [49], and then the change in the indices of material characteristics is significantly reduced.…”

“…Under the influence of these factors, destruction, hydrolysis, additional hardening, swelling, plasticization, structural relaxation and other physicochemical transformations occur in them, which accelerate or slow down the changes in their mechanical parameters [16]. In recent years, an in-depth analysis of significant factors affecting the properties of PCM has been carried out [5,[17][18][19][20][21][22]; however, when discussing the regularities observed, an insufficient attention is paid to such an important factor of influence as the action of internal stresses [23].…”

“…In [26], the level of internal stresses in a unidirectional fiberglass based on a polyester binder cooled to -60°C reached 62 MPa. This value is commensurable with the ultimate tensile [12] or compression strength [27] of the material and should be taken into account when analyzing the reasons for the formation of microcracks during daily and seasonal temperature fluctuations in open climatic conditions [23].…”