Even though the sentinel might feel some sympathy for Antigone, he is bringing her to Creon for one reason, to save his own life. The sentinel will be held responsible by the King, so he is very eager to make sure that the King knows who buried Polyneices.
The sentinel wants to make sure that the King does not think that the guards were involved in the burial in any way because Creon has decreed that anyone who disobeys his orders will be executed.
"The sentry then proudly brings Antigone to Creon, glad to have cleared himself of any wrongdoing. He claims to be concerned solely with his own welfare, though expresses regret at having implicated such a young woman."
When the guard has to tell the King that he has discovered that Polyneices has been buried, he is terrified for his life.
"GUARD I wish to tell thee first about myself-I did not do the deed-I did
not see the doer-it were not right that I should come to any harm." (Sophocles)
When the sentinel brings Antigone to the King, and tells him the story of how they set a trap to capture the culprit, by removing the dirt from the body and waiting, hidden to see who would return, he is relieved that he will not be held responsible for disobeying the King's decree.
"To have escaped from ills one's self is a great joy; but 'tis painful to bring friends to ill. Howbeit, all such things are of less account to me than mine own safety." (Sophocles)Another important point that you should keep in mind about the guard's motivation is that he along with everyone else in Thebes is afriad of Creon, they do not respect him, they tell him what he wants to hear out of fear.
The sentinel demonstrates several attitudes as he brings Antigone to Creon.
1. He is defiant. He had told Creon that he would not bring in the person who tried to bury the body, in part because Creon was so insulting to him. But, when he discovers that Antigone attempted the burial, he brings her in and tells Creon,
"You take her, / as you wish, and question and sentence her. I've justly freed myself from these troubles" (lines 406-408).
His defiance stems from the fact that he does not agree with Creon and does not particularly like the king, but he brings in Antigone just to prove Creon wrong. Even as he turns her over to her uncle, he assumes a Pontius Pilate attitude that the situation is now out of his hands, and he wants no more to do with it.
2. He is reluctant, because he knows that Antigone's sentence must be death, and obviously he, like most of the people of the city, would empathize with Antigone's decision to bury her brother's remains because it is in keeping with his culture and beliefs. He has also felt Creon's wrath and realizes that Antigone will have to endure much more than a tongue-lashing such as he received.
3. Finally, he is pained. As he finishes describing the burial scene that he and his men witnessed, he tells Creon that
"[Antigone] stood in / denial of nothing, something for me / both sweet and painful all at once" (443-445).
As a military man, he admires Antigone's risk for her brother's honor and appreciates that she stands strong as they arrest her and sure of action. It pains him to know that he is turning over someone such as she to someone such as Creon, whom he disdains.